WO2024107415A1 - Liquid crystal windows comprising at least one twisted nematic liquid crystal layer and at least one polarizer - Google Patents

Liquid crystal windows comprising at least one twisted nematic liquid crystal layer and at least one polarizer Download PDF

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Publication number
WO2024107415A1
WO2024107415A1 PCT/US2023/037229 US2023037229W WO2024107415A1 WO 2024107415 A1 WO2024107415 A1 WO 2024107415A1 US 2023037229 W US2023037229 W US 2023037229W WO 2024107415 A1 WO2024107415 A1 WO 2024107415A1
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WIPO (PCT)
Prior art keywords
liquid crystal
alignment
layer
window
twisted nematic
Prior art date
Application number
PCT/US2023/037229
Other languages
French (fr)
Inventor
Liang-Chy Chien
Mingqian He
Chien-Tsung Hou
Xiang-Dong Mi
Andrew Joseph Sullivan
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Corning Incorporated
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Publication of WO2024107415A1 publication Critical patent/WO2024107415A1/en

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • E—FIXED CONSTRUCTIONS
    • E06—DOORS, WINDOWS, SHUTTERS, OR ROLLER BLINDS IN GENERAL; LADDERS
    • E06B—FIXED OR MOVABLE CLOSURES FOR OPENINGS IN BUILDINGS, VEHICLES, FENCES OR LIKE ENCLOSURES IN GENERAL, e.g. DOORS, WINDOWS, BLINDS, GATES
    • E06B9/00—Screening or protective devices for wall or similar openings, with or without operating or securing mechanisms; Closures of similar construction
    • E06B9/24—Screens or other constructions affording protection against light, especially against sunshine; Similar screens for privacy or appearance; Slat blinds
    • E—FIXED CONSTRUCTIONS
    • E06—DOORS, WINDOWS, SHUTTERS, OR ROLLER BLINDS IN GENERAL; LADDERS
    • E06B—FIXED OR MOVABLE CLOSURES FOR OPENINGS IN BUILDINGS, VEHICLES, FENCES OR LIKE ENCLOSURES IN GENERAL, e.g. DOORS, WINDOWS, BLINDS, GATES
    • E06B9/00—Screening or protective devices for wall or similar openings, with or without operating or securing mechanisms; Closures of similar construction
    • E06B9/24—Screens or other constructions affording protection against light, especially against sunshine; Similar screens for privacy or appearance; Slat blinds
    • E06B2009/2464—Screens or other constructions affording protection against light, especially against sunshine; Similar screens for privacy or appearance; Slat blinds featuring transparency control by applying voltage, e.g. LCD, electrochromic panels
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/13363—Birefringent elements, e.g. for optical compensation
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/137—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
    • G02F1/139—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
    • G02F1/1396—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent the liquid crystal being selectively controlled between a twisted state and a non-twisted state, e.g. TN-LC cell

Definitions

  • the disclosure relates generally to twisted nematic liquid crystal windows, and more particularly to liquid crystal windows comprising at least one twisted nematic liquid crystal layer and at least one pair of polarizers.
  • Liquid crystal devices are used in various architectural and transportation applications, such as windows, doors, space partitions, and skylights for buildings and automobiles. Liquid crystal devices can serve as “smart” or tintable windows for many commercial applications.
  • Various liquid crystal materials can be used in smart windows to provide two or more transmission states, such as a dark or opaque state and a light or transparent state. The window can be switched between states by applying or removing voltage.
  • Twisted nematic liquid crystal (TNLC) devices typically include a pair of polarizers, one on either side of a cell containing liquid crystal that is rotated by 90 degrees from one surface of the cell to another.
  • a single cell normally transparent (NT) TNLC which is light transmissive in the absence of voltage
  • the polarizers are oriented with their transmission axes perpendicular to each other.
  • ND normally dark
  • TNLC has been used in display applications.
  • the thickness or cell gap of the liquid crystal can be chosen so the transmission of the liquid crystal is zero or as close as possible to zero in the dark state.
  • a larger LC cell gap is often not feasible in display applications Attorney Docket No. SP22-232PCT because it results in slower response times, higher driving voltages, and/or increased device thickness and/or weight, which are undesirable for display applications.
  • Liquid crystal windows can have larger cell gaps and slower response times as compared to display devices and, thus, TNLC may be a suitable candidate for the LC layer in such windows.
  • NT TNLC is known to have an undesirably high transmittance in the dark state when viewed from a large viewing angle, such as 40 degrees or greater.
  • ND TNLC is known to have an undesirable appearance of coloration in the dark state.
  • Liquid crystal windows are often viewed from a variety of different angles and, thus, the quality of the dark state over larger viewing angles in terms of low transmittance and wavelength insensitivity can be important. [0007] It would be desirable to provide a TNLC window that has an improved dark state over a wide range of viewing angles. It would also be desirable to provide a TNLC window with a wavelength insensitive dark state. It would further be advantageous to improve the contrast ratio of such TNLC windows for normal and large viewing angles.
  • the disclosure relates, in various embodiments, to a normally dark liquid crystal window comprising at least one twisted nematic liquid crystal layer and at least two polarizers.
  • the liquid crystal windows can comprise a first polarizer having a first transmission axis; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; and a second polarizer having a second transmission axis; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a dark state in the absence of applied voltage, and the liquid crystal window is in
  • the disclosure relates, in certain embodiments, to a normally dark liquid crystal window comprising at least one twisted nematic liquid crystal layer, at least two polarizers, and at least one compensation layer.
  • the liquid crystal windows can comprise a first polarizer having a first transmission axis; a first compensation layer; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index n e , an ordinary refractive index n o , and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation layer; and a second polarizer having a second transmission axis; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a dark state in the absence of applied voltage, and the liquid crystal window is in a transparent state when voltage is applied across the first and second electrodes; wherein the twisted nematic liquid crystal layer has
  • the disclosure relates, in additional embodiments, to normally transparent liquid crystal windows comprising at least one twisted nematic liquid crystal layer, at least two polarizers, and at least one compensation layer.
  • the liquid crystal windows can comprise a first polarizer having a first transmission axis; a first compensation layer; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index n e , an ordinary refractive index n o , and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation layer; and a second polarizer Attorney Docket No.
  • the disclosure relates, in some embodiments, to normally transparent liquid crystal windows comprising at least one twisted nematic liquid crystal layer, at least two polarizers, at least one compensation layer, and at least one continuous electrode layer.
  • the liquid crystal windows can comprise a first polarizer having a first absorption axis; a first compensation layer having a first optical axis varying in a first optical plane; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation layer having a second optical axis varying in a second optical plane; and a second polarizer having a second absorption axis; wherein the liquid crystal window comprises vertical and horizontal directions in a viewing plane of the liquid crystal window and a normal viewing direction perpendicular to the viewing plane; wherein the first absorption axis, a first normal direction of the first optical plane, and the first alignment direction are aligned along a first vector; wherein the second absorption axis, a second normal direction
  • the disclosure relates, in various embodiments, to normally transparent liquid crystal windows comprising at least one twisted nematic liquid Attorney Docket No. SP22-232PCT crystal layer comprising a cell gap of greater than 5 ⁇ m, at least two polarizers, and at least one compensation layer.
  • the liquid crystal windows can comprise a first polarizer having a first absorption axis; a first compensation layer having a first optical axis varying in a first optical plane; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index n e , an ordinary refractive index n o , and a cell gap d greater than 5 ⁇ m; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation layer having a second optical axis varying in a second optical plane; and a second polarizer having a second absorption axis; wherein the first absorption axis, a first normal direction of the first optical plane, and the first alignment direction are aligned along a first vector; wherein the second absorption axis, a second normal direction of the second optical plane, and the second alignment direction are aligned along a second vector that is orthogonal
  • the disclosure relates, in further embodiments, to normally dark liquid crystal windows comprising at least two twisted nematic liquid crystal layer and at least two polarizers.
  • the first twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a dark state in the absence of applied voltage, and the liquid crystal window is in a transparent state when voltage is applied across the first and second electrodes; wherein the first twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the second twisted nematic liquid crystal layer is disposed between the third and fourth alignment layers and the third alignment direction is orthogonal to the fourth alignment direction; wherein the first rotation direction X1 is opposite to the second rotation direction X2; wherein the first retardation Re1 is substantially equal to the second retardation Re2; wherein the first and second birefringence distributions are orthogonal to each other in the absence of applied voltage; and wherein the first and second transmission axes are orthogonal to each other.
  • the disclosure relates, in still further embodiments, to normally transparent liquid crystal windows comprising at least two twisted nematic liquid crystal layers and at least two polarizers.
  • SP22-232PCT second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the second twisted nematic liquid crystal layer is disposed between the third and fourth alignment layers and the third alignment direction is orthogonal to the fourth alignment direction; wherein the first rotation direction X1 is opposite to the second rotation direction X2; wherein the first retardation Re1 is substantially equal to the second retardation Re2; wherein the first and second birefringence distributions are orthogonal to each other in the absence of applied voltage; and wherein the first and second transmission axes are parallel to each other.
  • FIGS.1A-B depict cross-sectional views of liquid crystal windows according to various embodiments of the disclosure.
  • FIG.2 depicts a cross-sectional view of a liquid crystal window according to additional embodiments of the disclosure; Attorney Docket No.
  • FIG.3A-B are schematics depicting the operation of a ND TNLC twisted nematic liquid crystal window in the absence of voltage (dark) and with applied voltage (transparent), respectively;
  • FIG.4 is a plot depicting the calculated transmittance of a ND TNLC as a function of wavelength for different cell gaps;
  • FIG.5 is a plot depicting transmittance of a ND TNLC in the visible light spectrum for different cell gaps in the presence and absence of voltage;
  • FIG.6A-B are plots depicting the normalized transmittance of a ND TNLC at three visible wavelengths vs.
  • FIG.6C-D are plots depicting the normalized transmittance of a ND TNLC at three visible wavelengths vs. polar viewing angle in the width (0 o ) and length (90 o ) directions of the window, respectively, in the presence of applied voltage;
  • FIGS.6E-F are plots of the contrast of the liquid crystal window at three visible wavelengths vs.
  • FIG.7 is a plot depicting the transmittance of a NT TNLC in the visible light spectrum in the presence and absence of voltage
  • FIG.8 is a plot depicting the transmittance of NT and ND dual TNLC in the visible light spectrum in the presence and absence of voltage
  • FIG 9A-F are polar plots depicting the transmittance of a NT TNLC at 550 nm for different applied voltages.
  • liquid crystal windows comprising: a first polarizer having a first transmission axis; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; and a second polarizer having a second transmission axis; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the twisted nematic liquid Attorney Docket No.
  • liquid crystal windows comprising a first polarizer having a first transmission axis; a first compensation layer; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index n e , an ordinary refractive index n o , and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation layer; and a second polarizer having a second transmission axis; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a dark state in the absence of applied voltage, and the liquid crystal window is in a transparent state when voltage is applied across the first and second electrodes; wherein the twisted n
  • liquid crystal windows comprising a first polarizer having a first transmission axis; a first compensation layer; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation layer; and a second polarizer having a second transmission axis; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the Attorney Docket No.
  • the twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a transparent state in the absence of applied voltage, and the liquid crystal window is in a dark state when voltage is applied across the first and second electrodes; and wherein the first and second transmission axes are orthogonal to each other.
  • liquid crystal windows comprising a first polarizer having a first absorption axis; a first compensation layer having a first optical axis varying in a first optical plane; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index n e , an ordinary refractive index n o , and a cell gap d; a second alignment layer having a second alignment direction; a second electrode having a second absorption axis; a second glass substrate; a second compensation layer having a second optical axis varying in a second optical plane; and a second polarizer having a second transmission axis; wherein the liquid crystal window comprises vertical and horizontal directions in a viewing plane of the liquid crystal window and a normal viewing direction perpendicular to the viewing plane; wherein the first absorption axis, a first normal direction of the first optical plane, and the first alignment direction are aligned
  • liquid crystal windows comprising a first polarizer having a first absorption axis; a first compensation layer having a first optical axis varying in a first optical plane; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d greater than 5 ⁇ m; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation Attorney Docket No.
  • SP22-232PCT layer having a second optical axis varying in a second optical plane; and a second polarizer having a second absorption axis; wherein the first absorption axis, a first normal direction of the first optical plane, and the first alignment direction are aligned along a first vector; wherein the second absorption axis, a second normal direction of the second optical plane, and the second alignment direction are aligned along a second vector that is orthogonal to the first vector; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and is in electrical contact with the first and second electrodes; and wherein the liquid crystal window is in a transparent state in the absence of applied voltage across the first and second electrodes.
  • SP22-232PCT retardation Re1 is substantially equal to the second retardation Re2; wherein the first and second birefringence distributions are orthogonal to each other in the absence of applied voltage; and wherein the first and second transmission axes are orthogonal to each other.
  • FIGS.1-2 illustrate various aspects of the liquid crystal windows disclosed herein.
  • the following general description is intended to provide an overview of the claimed devices, and various aspects will be more specifically discussed throughout the disclosure with reference to the non-limiting depicted embodiments, these embodiments being interchangeable with one another within the context of the disclosure.
  • FIGS.1A, 1B, and 2 illustrate cross-sectional views of non-limiting embodiments of liquid crystal windows 100, 100*, and 200, respectively.
  • liquid crystal window 100 may have a single cell configuration, e.g., a single liquid crystal layer controlled by a single pair of electrodes, as depicted in FIGS.1A- B.
  • the liquid crystal windows may also comprise two liquid crystal layers, as depicted in FIG.2, or more than two liquid crystal layers (not depicted).
  • liquid crystal window 100 includes first and second glass substrates 101, 102, an electrode pair comprising first and second electrodes 106, 107, and twisted nematic liquid crystal layer 110.
  • First glass substrate 101 comprises a first surface 101A and a second surface 101B.
  • a first electrode 106 is formed on and/or in direct contact with second surface 101B of first glass substrate 101.
  • second glass substrate 102 comprises a first surface 102A and a second surface 102B.
  • a second electrode 107 is formed on and/or in direct contact with first surface 102A of second glass substrate 102.
  • the twisted nematic liquid crystal layer 110 is disposed between and in electrical contact with first and second electrodes 106, 107.
  • the twisted nematic liquid crystal layer 110 is in direct physical contact with first and second electrodes 106, 107.
  • the first and second glass substrates 101, 102 and their corresponding electrodes 106, 107 can define a sealed gap or cell that contains the liquid crystal material. Seals s1 can be used to contain the liquid crystal material in the twisted nematic liquid crystal layer 110.
  • Liquid crystal window 100 can further include a first alignment or orientation layer 113 disposed between first electrode 106 and twisted nematic liquid crystal layer 110 and/or a second alignment or orientation layer 114 disposed between second electrode 107 and twisted nematic liquid crystal layer 110.
  • alignment layers 113, 114 can both be present. In other embodiments, only one of alignment layers 113, 114 may be present.
  • a first compensation layer 111 can be formed on and/or in direct contact with first surface 101A of first glass substrate 101. The first compensation layer 111 can be disposed between the first substrate 101 and a first polarizer 108.
  • a second compensation layer 112 can be formed on and/or in direct contact with second surface 102B of second glass substrate 102.
  • the second compensation layer 112 can be disposed between the second substrate 102 and a first polarizer 109.
  • a first substrate assembly 1S can comprise the first glass substrate 101, the first electrode 106, and the first alignment layer 113.
  • a second substrate assembly 2S can comprise the second glass substrate 102, the second electrode 107, and the second alignment layer 114.
  • the twisted nematic liquid crystal layer 110 can be disposed between the first and second substrate assemblies 1S, 2S.
  • Liquid crystal window 100 can be produced, for example, by coating, printing, or otherwise depositing the first electrode layer 106 on the second surface 101B of the first glass substrate 101, and coating, printing, or otherwise depositing the second electrode layer 106 on the first surface 102A of the second glass substrate 102. Alignment layers 113, 114 can be deposited on electrode layers 106, 107, respectively, and rubbed in the desired direction. The substrate assemblies can then be arranged to form a gap, which can be filled with liquid crystal material to form twisted nematic liquid crystal layer 110.
  • spacers (not illustrated) can be used to maintain the desired cell gap and resulting liquid crystal layer thickness. In some embodiments, the spacers are black.
  • the black spacers minimize the light leakage in the dark state.
  • the liquid crystal material can be sealed in the cell gaps around all edges using any suitable material, such as optically or thermally curable resins, to form seals s1.
  • First compensation layer 111 and first polarizer 108 can be formed and/or deposited on first surface 101A of first glass substrate 101, and second compensation layer 112 and second polarizer 109 can be formed and/or deposited on second surface 102B of second glass substrate 102.
  • FIG.1B illustrates a non-limiting configuration for a liquid crystal window 100* further comprising third and/or fourth substrates 103, 104.
  • Third substrate 103 comprises a first surface 103A and a second surface 103B.
  • SP22-232PCT substrate 104 comprises a first surface 104A and a second surface 104B.
  • Third and fourth substrates 103, 104 can be attached or laminated to first and second substrates 101, 102, respectively, by first and second interlayers 115, 116, respectively.
  • first and third substrates 101, 103 can define a first cell gap 117, which can be sealed with seals s2 and may contain at least one insulating gas.
  • second and fourth substrates 102, 104 can define a second cell gap 118, which can be sealed with seals s2 and may contain at least one insulating gas.
  • Cell gaps 117, 118 can be filled with air, an inert gas, or a mixture thereof.
  • Suitable inert gases include, but are not limited to, argon, krypton, xenon, and combinations thereof. Mixtures of inert gases or mixtures of one or more inert gases with air can also be used. Exemplary non-limiting inert gas mixtures include 90/10 or 95/5 argon/air, 95/5 krypton/air, or 22/66/12 argon/krypton/air mixtures. Other ratios of inert gases or inert gases and air can also be used depending on the desired thermal performance and/or end use of the liquid crystal window.
  • FIG.1B depicts a liquid crystal window 100* comprising both a third and a fourth substrate
  • the liquid crystal window 100* can comprise only one of such substrates, for instance, second surface 103B of third substrate 103 can be attached to first surface 101A of the first glass substrate 101 by first interlayer 115 and a fourth substrate may not be present.
  • first surface 104A of fourth substrate 104 can be attached to the second surface 102B of the second glass substrate 102 by second interlayer 116 and the third substrate may not be present.
  • FIG.1B depicts a liquid crystal window 100* comprising both a first cell gap 117 and a second cell gap 118
  • the liquid crystal window 100* may comprise no cell gaps or only one of such cell gaps.
  • first and third substrates 101, 103 may be directly laminated to one another without a first cell gap 117 and/or second and fourth substrates 102, 104 may be directly laminated to one another without a second cell gap 118.
  • the liquid crystal window 100* depicted in FIG.1B may be advantageous from a safety standpoint. If the third substrate 103 is broken or damaged, the first interlayer 115 can hold any broken pieces in place.
  • the liquid crystal window 100* depicted in FIG.1B may also be advantageous from a thermal efficiency standpoint as the insulating gas present in Attorney Docket No. SP22-232PCT the first and/or second cell gaps 117, 118 can reduce thermal transfer across the window layers and thus improve the overall thermal rating of the window 100*. Additional advantages can also include protection from ultraviolet (UV) and/or infrared radiation. At least one of the third or fourth substrate 103, 104 can comprise a low emissivity glass or can comprise a coating that reduces the amount of infrared and ultraviolet light that passes through the substrate. The interlayer can also be used to reduce UV transmittance.
  • liquid crystal window 100* can be oriented such that third substrate 103 is the outermost substrate facing the exterior, e.g., outside of a building or vehicle, and fourth substrate 104 is the innermost substrate and faces the interior, e.g., inside of a building or vehicle.
  • third substrate 103 and/or first interlayer 115 can provide UV and/or infrared blocking properties for light L incident upon the liquid crystal window 100*.
  • the reverse orientation is also possible, in which case the fourth substrate 104 and/or second interlayer 116 can provide UV and/or infrared light blocking.
  • the liquid crystal devices disclosed herein can, in some embodiments, include more than one switchable layer, such as an additional liquid crystal layer.
  • liquid crystal window 200 can further include an interstitial substrate 105 disposed between the first and second glass substrates 101, 102.
  • the interstitial substrate 105 may comprise glass, similar to the first and second substrates 101, 102, or may comprise any other suitable transparent material, such as plastic. While FIG.2 depicts a single-cell configuration with an interstitial substrate, it is also possible to use a traditional double-cell configuration, e.g., two side-by-side single cells comprising four substrates (two substrates per cell) instead of two substrates separated by a single interstitial substrate as shown in FIG. 2.
  • Liquid crystal window 200 can include twisted nematic liquid crystal layer 110, which is disposed between the first glass substrate 101 and the interstitial substrate 105, and a second or additional twisted nematic liquid crystal layer 120, which is disposed between the second glass substrate 102 and the interstitial substrate 105.
  • the rotation direction of the first liquid crystal layer 110 can be the opposite of the rotation direction of the second liquid crystal layer 120, as discussed in more detail below.
  • twisted nematic liquid crystal layer 110 can be disposed between first and second alignment layers 113, 114.
  • First and second electrodes 106, 107 can be used to apply voltage to the twisted nematic Attorney Docket No. SP22-232PCT liquid crystal layer 110.
  • the second twisted nematic liquid crystal layer 120 can be disposed between third and fourth alignment layers 123, 124.
  • First polarizer 108 is formed or deposited on first surface 101A of first substrate 101 and second polarizer 109 is formed or deposited on second surface 102B of second substrate 102.
  • a first substrate assembly 1S can comprise the first glass substrate 101, the first electrode 106, and the first alignment layer 113.
  • a second substrate assembly 2S’ can comprise the second glass substrate 102, and the fourth alignment layer 124.
  • An interstitial substrate assembly 103 can comprise the interstitial substrate 105, the second electrode 107, the second alignment layer 114, and the third alignment layer 123.
  • the twisted nematic liquid crystal layer 110 can be disposed between the first substrate assembly 1S and the interstitial substrate assembly 3S.
  • the additional liquid crystal layer 120 can be disposed between the interstitial substrate assembly 3S and the second substrate assembly 2S’.
  • the liquid crystal window in some embodiments, comprises an upper edge, lower edge, left edge, and right edge and may, for example, be divided into an upper left, upper right, lower left, and lower right quadrant.
  • An upper direction of the window is defined from the lower edge to the upper edge of the window.
  • a lower direction of the window is defined from the upper edge to the lower edge of the window.
  • Upper and lower directions are vertical (or length) directions. The vertical direction can be perpendicular to a horizontal (or width) direction of the window, which is defined from the left edge to the right edge (right direction) or vice versa (left direction).
  • a normal direction of the liquid crystal window can be defined as a direction perpendicular to the plane of the liquid window.
  • a first non-limiting embodiment of the disclosure comprises a normally dark single-cell twisted nematic liquid crystal window with a retardation Re Attorney Docket No. SP22-232PCT value of greater than or equal to 1.4 Pm, and Re/O ⁇ for visible light wavelengths (400-700nm).
  • such a liquid crystal window comprises: (a) a first polarizer 108 having a first transmission axis, (b), a first substrate assembly 1S comprising a first glass substrate 101, a first electrode 106, and a first alignment layer 113, (c) a second polarizer 109 having a second transmission axis, (d) a second substrate assembly 2S comprising a second glass substrate 102, a second electrode 107, and a second alignment layer 114, and (d) a twisted nematic liquid crystal layer 110 disposed between the first and second substrate assemblies.
  • the first and second substrate assemblies 1S, 2S are disposed between the first and second polarizers 108, 109.
  • the first and second substrate assemblies 1S, 2S are oriented such that the first and second alignment layers 113, 114 face each other and the liquid crystal layer 110 is disposed between these two alignment layers. Compensation layers 111, 112 may or may not be present in this embodiment.
  • Fabrication of an exemplary liquid crystal window according to this embodiment is discussed in Example 1. The components of the liquid crystal window of this embodiment are listed below in Table I: Table I: Normally Dark Single TN LC Attorney Docket No. SP22-232PCT [0052] The first polarizer 108 and the second polarizer 109 have parallel transmission axes.
  • the twisted nematic liquid crystal layer 110 has an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d.
  • the first alignment layer 113 has a first alignment (or rubbing) direction R1 and the second alignment layer 114 has a second alignment (or rubbing) direction R2 orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90 o ⁇ 10 o across the cell gap (d), e.g., from the first alignment layer to the second alignment layer in the absence of external voltage.
  • the retardation Re of the twisted nematic liquid crystal layer (ne-no)*d is greater than or equal to 1.4 Pm, and Re/O ⁇ 2 for wavelengths ⁇ in the visible spectrum ( ⁇ 400-700 nm).
  • the cell gap d of the twisted nematic liquid crystal layer ranges from about 3 ⁇ m to about 30 ⁇ m, such as from about 10 ⁇ m to about 25 ⁇ m, or from about 15 ⁇ m to about 20 ⁇ m.
  • the transmission axis T1 of the first polarizer and the first alignment direction R1 can be parallel or orthogonal to each other. In alternative embodiments, T1 and R1 can be at an angle relative to each other that is between 0 and 90 degrees.
  • the twisted nematic liquid crystal window of this embodiment is dark in the absence of external voltage (e.g., transmittance ⁇ 3%) and transparent when voltage is applied (e.g., transmittance > 30%).
  • a transmittance of normally incident visible light in the dark state is less than 0.5%.
  • a transmittance of incident light having a wavelength ⁇ of 550 nm and an incident angle of up to 80 o is less than 1% in the dark state and/or a transmittance of incident light having a wavelength ⁇ of 500 nm and an incident angle of up to 80 o is greater than 30% in the transparent state.
  • Attorney Docket No. SP22-232PCT [0054]
  • the configurations discussed above with reference to FIG.1A are also applicable to the liquid crystal window of FIG.1B, which can include one or both of third and fourth glass substrates.
  • first and second electrodes 106, 107 depict liquid crystal layer 110 disposed between first and second electrodes 106, 107
  • first and second electrodes 106, 107 can comprise interdigitated electrodes disposed on an interior surface (e.g., second surface 101B) of the first glass substrate 101 or on an interior surface (e.g., first surface 101A) of the second glass substrate 102.
  • first and second polarizers 108, 109 can comprise an iodine-based polarizer or a dye-based polarizer.
  • FIGS.3A-B depict the operation of a normally dark twisted nematic liquid crystal layer.
  • normally dark or normally opaque are used to refer to liquid crystal windows that do not transmit or have minimal transmission of visible light in the absence of applied voltage, e.g., less than about 3% light transmittance, less than about 2% light transmittance, less than about 1% light transmittance, or less than about 0.5% light transmittance.
  • Normally dark liquid crystal windows transmit light upon the application of voltage.
  • normally light or normally transparent are used to refer to liquid crystal windows that transmit visible light in the absence of applied voltage, e.g., greater than about 30% light transmittance, greater than about 35% light transmittance, greater than about 40% light transmittance, or greater than about 45% light transmittance.
  • the liquid crystal LC disposed between first and second polarizers P1, P2 rotates by 90 o ⁇ 10 o from one polarizer to the other.
  • the ⁇ 90 o rotation can be created, e.g., by including alignment or orientation layers A1, A2 on either side of the liquid crystal LC, having alignment (or rubbing) directions that are approximately orthogonal to one another, as discussed in more detail below.
  • the polarizers P1, P2 have parallel axes of transmission.
  • Polarizer P1 allows light of one polarization that is parallel to the transmission axis of polarizer P1 to pass through. In the absence of voltage, light Attorney Docket No. SP22-232PCT passing through P1 is blocked by polarizer P2, due to the polarization of the light that is rotated ⁇ 90 o by the twisted nematic liquid crystal, resulting in a dark state.
  • the alignment direction of alignment layer A2 is approximately orthogonal or parallel to the transmission axis of polarizers P1, P2.
  • T becomes zero, corresponding to a perfectly dark state.
  • m 1 or 2.
  • the thickness or cell gap (d) of the liquid crystal becomes too large for display applications due to the corresponding slow response time, which is proportional to d 2 .
  • FIG.4 is a graph illustrating the calculated transmittance of a normally dark twisted nematic liquid crystal as a function of wavelength (400-700 nm) at different cell gaps (d) for a birefringence ('n) value of 0.2. As shown in FIG. 4, transmittance in the dark state generally approaches zero over visible light wavelengths as the thickness of the liquid crystal layer (cell gap (d)) increases.
  • the solar spectrum weighted transmittance (T_D65) is indicative of the ability of a window to achieve a dark state.
  • the transmittance is ⁇ 1.5% for all wavelengths between 400 nm and 700 nm and the transmittance is ⁇ 1.0% for the wavelength 550 nm.
  • An additional non-limiting embodiment of the disclosure comprises a normally dark single-cell twisted nematic liquid crystal window with at least one compensation layer.
  • such a liquid crystal window comprises: (a) a first polarizer 108 having a first transmission axis, (b), a first substrate assembly 1S comprising a first glass substrate 101, a first electrode 106, and a first alignment layer 113, (c) a second polarizer 109 having a second transmission axis, (d) a second substrate assembly 2S comprising a second glass substrate 102, a second electrode 107, and a second alignment layer 114, and (d) a twisted nematic liquid crystal layer 110 disposed between the first and second substrate assemblies.
  • the first and second substrate assemblies 1S, 2S are disposed between the first and second polarizers 108, 109.
  • the first and second substrate assemblies 1S, 2S are oriented such that the first and second alignment layers 113, 114 face each other and the liquid crystal layer 110 is disposed between these two alignment layers. At least one or both of compensation layers 111, 112 is present in this embodiment.
  • Attorney Docket No. SP22-232PCT [0067] Fabrication of an exemplary liquid crystal window according to this embodiment is discussed in Example 1. The components of the liquid crystal window of this embodiment are listed below in Table IV: Table IV: Normally Dark Single TN LC with Compensation Layers [0068] The first polarizer 108 and the second polarizer 109 have parallel transmission axes.
  • the twisted nematic liquid crystal layer 110 has an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d.
  • the first alignment layer 113 has a first alignment direction and the second alignment layer 114 has a second alignment direction orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90 o ⁇ 10 o across the cell gap, e.g., from Attorney Docket No. SP22-232PCT the first alignment layer to the second alignment layer in the absence of external voltage.
  • the retardation Re of the twisted nematic liquid crystal layer (ne-no)*d can range from about 0.39 Pm to about 1.26 Pm, from about 0.47 Pm to about 1.07 Pm, or greater than or equal to 1.4 Pm for a wavelength ⁇ in the visible spectrum (400- 700 nm).
  • the cell gap d of the twisted nematic liquid crystal layer ranges from about 3 ⁇ m to about 30 ⁇ m, such as from about 10 ⁇ m to about 25 ⁇ m, or from about 15 ⁇ m to 20 ⁇ m.
  • the transmission axis T1 of the first polarizer and the first alignment direction R1 can be parallel or orthogonal to each other.
  • T1 and R1 can be at an angle relative to each other that is between 0 and 90 degrees.
  • the twisted nematic liquid crystal window of this embodiment is dark in the absence of external voltage (e.g., transmittance ⁇ 3%) and transparent when voltage is applied (e.g., transmittance > 30%).
  • a transmittance of normally incident visible light in the dark state is less than 0.5%.
  • a transmittance of incident light having a wavelength ⁇ of 550 nm and an incident angle of up to 80 o is less than 1% in the dark state and/or a transmittance of incident light having a wavelength ⁇ of 500 nm and an incident angle of up to 80 o is greater than 30% in the transparent state.
  • the configurations discussed above with reference to FIG.1A are also applicable to the liquid crystal window of FIG.1B, which can include one or both of third and fourth glass substrates.
  • FIGS.1A-B depict liquid crystal layer 110 disposed between first and second electrodes 106, 107
  • first and second electrodes 106, 107 can comprise interdigitated electrodes disposed on an interior surface (e.g., second surface 101B) of the first glass substrate 101 or on an interior surface (e.g., first surface 101A) of the second glass substrate 102.
  • first and second polarizers 108, 109 can comprise an iodine-based polarizer or a dye-based polarizer.
  • a further embodiment of the disclosure comprises a normally transparent single-cell twisted nematic liquid crystal window with at least one compensation layer.
  • such a liquid crystal window comprises: (a) a first polarizer 108 having a first transmission axis, (b), a first substrate assembly comprising a first glass substrate 101, a first electrode 106, and a first alignment Attorney Docket No. SP22-232PCT layer 113, (c) a second polarizer 109 having a second transmission axis, (d) a second substrate assembly comprising a second glass substrate 102, a second electrode 107, and a second alignment layer 114, and (d) a twisted nematic liquid crystal layer 110 disposed between the first and second substrate assemblies.
  • the first and second substrate assemblies 1S, 2S are disposed between the first and second polarizers 108, 109.
  • the first and second substrate assemblies 1S, 2S are oriented such that the first and second alignment layers face each other and the liquid crystal window is disposed between these two alignment layers. At least one or both of compensation layers 111, 112 is present in this embodiment.
  • the birefringence distribution of the first and/or second compensation layers mimic the birefringence distribution of the liquid crystal when an external voltage is applied across the first and second electrodes.
  • the first polarizer 108 and the second polarizer 109 have orthogonal transmission axes.
  • the first transmission axis of the first polarizer 108 can be parallel to a horizontal direction of the first and second glass substrates and the second transmission axis of the second polarizer 109 can be orthogonal to the horizontal direction of the first and second glass substrates.
  • the first transmission axis of the first polarizer 108 can be parallel to a vertical direction of the first and second glass substrates and the second transmission axis of the second polarizer 109 can be orthogonal to the vertical direction of the first and second glass substrates.
  • polarizers can be utilized more efficiently, because the polarizers are typically fabricated roll-to-roll and the transmission axis of the polarizers is typically orthogonal to the horizontal direction of the roll.
  • the first transmission axis of the first polarizer 108 can be at about 45 degrees to a horizontal direction of the first and second glass substrates and the second transmission axis of the second polarizer 109 can be at about -45 degrees to the horizontal direction of the first and second glass substrates.
  • the liquid crystal window may have a more symmetrical viewing angle characteristic between the left and right.
  • the twisted nematic liquid crystal layer 110 has an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d.
  • the first alignment layer 113 has a first alignment direction and the second alignment layer 114 has a second alignment direction orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90 o ⁇ 10 o across the cell gap, e.g., from the first alignment layer to the second alignment layer in the absence of external voltage.
  • the liquid crystal molecules can be aligned in any given direction, such as facing upward, downward, to the left, or to the right, as defined relative to a user standing in front of the liquid crystal window.
  • certain liquid crystal molecule configurations may be more effective for creating a dark state with higher contrast ratio than others.
  • the molecules in the central region of the liquid crystal layer are oriented to point downward. This configuration may be effective in blocking light coming in from the top direction of the window, e.g., southern-facing windows in the northern hemisphere and northern-facing windows in the southern hemisphere.
  • the liquid crystal molecules can be oriented to point upward when voltage is applied. This configuration can be more effective at blocking light in taller buildings when a user mainly looks down through a window.
  • the liquid crystal molecules can be oriented to point to the right or left when voltage is applied. These configurations can provide improved blocking of light coming from the east and west directions, respectively.
  • the retardation Re of the twisted nematic liquid crystal layer (ne- no)*d can range from about 0.46 ⁇ m to about 0.49 ⁇ m for wavelength ⁇ of 550 nm, or from about 1.05 ⁇ m to about 1.08 ⁇ m for wavelength ⁇ of 550 nm .
  • the cell gap d of the twisted nematic liquid crystal layer ranges from about 3 ⁇ m to about 30 ⁇ m, such as from about 5 ⁇ m to about 25 ⁇ m, from about 6 ⁇ m to about 20 ⁇ m, or from about 10 ⁇ m to about 15 ⁇ m, including all ranges and subranges therebetween.
  • the twisted nematic liquid crystal window of this embodiment is transparent in the absence of external voltage (e.g., transmittance > 30%) and dark when voltage is applied (e.g., transmittance ⁇ 3%).
  • a transmittance of normally incident visible light in the dark state is less than 0.5%.
  • a transmittance of incident light having a wavelength ⁇ of 550 nm and an incident angle of up to 80 o is less than 3% in the dark state.
  • the configurations discussed above with reference to FIG.1A are also applicable to the liquid crystal window of FIG.1B, which can include one or both of third and fourth glass substrates.
  • a further embodiment of the disclosure comprises a normally transparent single-cell twisted nematic liquid crystal window with at least one compensation layer and a liquid crystal cell gap greater than 5 ⁇ m.
  • such a liquid crystal window comprises: (a) a first polarizer 108 having a first transmission axis, (b), a first substrate assembly comprising a first glass substrate 101, a first electrode 106, and a first alignment layer 113, (c) a second polarizer 109 having a second transmission axis, (d) a second substrate assembly comprising a second glass substrate 102, a second electrode 107, and a second alignment layer 114, and (d) a twisted nematic liquid crystal layer 110 disposed between the first and second substrate assemblies having a cell gap greater than 5 ⁇ m.
  • the absorption axis of a polarizer is orthogonal to its transmission axis.
  • the first and second substrate assemblies 1S, 2S are disposed between the first and second polarizers 108, 109.
  • the first and second substrate assemblies 1S, 2S are oriented such that the first and second alignment layers face each other and the liquid crystal window is disposed between these two alignment layers.
  • Both compensation layers 111, 112 can be present in this embodiment.
  • the first absorption axis Y1, a first normal direction of Plane 1 (along which first optical axis O1 varies), and first alignment direction R1 are parallel to each other, e.g., aligned along a first vector.
  • the second absorption axis Y2, a second normal direction of Plane 2 (along which second optical axis O2 varies), and second alignment direction R2 are parallel to each other, e.g., aligned along a second vector.
  • first and second vectors are orthogonal to each other, e.g., first polarizer 108 and the second polarizer 109 can have orthogonal absorption axes, first compensation layer 111 and second compensation layer 112 can have orthogonal optical axes, and first alignment layer 113 and second alignment layer 114 can have orthogonal alignment (or rubbing) directions.
  • first vector (Y1, O1, R1) can be parallel (0 o or 180 o ) to a horizontal direction of the liquid crystal window and the second vector (Y2, O2, R2) can be orthogonal (90 o or 270 o ) to the horizontal direction of the liquid crystal window.
  • the first vector can be parallel to a vertical direction of the liquid crystal window and the second vector can be orthogonal to the vertical direction of the liquid crystal window.
  • the first vector can be at about 45 degrees relative to a horizontal direction of the liquid crystal window (45 o or 315 o ) and the second vector can be at about -45 degrees to the horizontal direction of the liquid crystal window (135 o or 225 o ).
  • Attorney Docket No. SP22-232PCT [0082]
  • the twisted nematic liquid crystal layer 110 has an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d.
  • the first alignment layer 113 has a first alignment direction and the second alignment layer 114 has a second alignment direction orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90 o ⁇ 10 o across the cell gap, e.g., from the first alignment layer to the second alignment layer in the absence of external voltage.
  • the cell gap d of the twisted nematic liquid crystal layer is greater than 5 ⁇ m, such as from about 6 ⁇ m to about 30 ⁇ m, from about 8 ⁇ m to about 25 ⁇ m, from about 10 ⁇ m to about 20 ⁇ m, or from about 12 ⁇ m to about 15 ⁇ m, including all ranges and subranges therebetween.
  • the twisted nematic liquid crystal window of this embodiment is transparent in the absence of external voltage (e.g., transmittance > 30%).
  • the configurations discussed above with reference to FIG.1A are also applicable to the liquid crystal window of FIG.1B, which can include one or both of third and fourth glass substrates.
  • first and second polarizers 108, 109 can comprise an iodine-based polarizer or a dye-based polarizer.
  • Yet another embodiment of the disclosure comprises a normally transparent single-cell twisted nematic liquid crystal window with at least one compensation layer and at least one continuous electrode.
  • such a liquid crystal window comprises: (a) a first polarizer 108 having a first absorption axis, (b), a first substrate assembly comprising a first glass substrate 101, a first electrode 106, and a first alignment layer 113, (c) a second polarizer 109 having a second absorption axis, (d) a second substrate assembly comprising a second glass substrate 102, a second electrode 107, and a second alignment layer 114, and (d) a twisted nematic liquid crystal layer 110 disposed between the first and second substrate assemblies.
  • the absorption axis of a polarizer is orthogonal to its transmission axis.
  • the first and second substrate assemblies 1S, 2S are disposed between the first and second polarizers 108, 109.
  • the first and second substrate assemblies 1S, 2S are oriented such that the first and Attorney Docket No. SP22-232PCT second alignment layers face each other and the liquid crystal window is disposed between these two alignment layers.
  • Both compensation layers 111, 112 are present in this embodiment.
  • Table VII Normally Transparent Single TNLC with Continuous Electrodes
  • the first absorption axis Y1, a first normal direction of Plane 1 (along which first optical axis O1 varies), and first alignment direction R1 are parallel to each other, e.g., aligned along a first vector.
  • the second absorption axis Y2, a second normal direction of Plane 2 (along which second optical axis O2 varies), and Attorney Docket No. SP22-232PCT second alignment direction R2 are parallel to each other, e.g., aligned along a second vector.
  • first and second vectors are orthogonal to each other, e.g., first polarizer 108 and the second polarizer 109 have orthogonal absorption axes, first compensation layer 111 and second compensation layer 112 have orthogonal optical axes, and first alignment layer 113 and second alignment layer 114 have orthogonal alignment (or rubbing) directions.
  • first vector (Y1, O1, R1) can be parallel (0 o or 180 o ) to a horizontal direction of the liquid crystal window and the second vector (Y2, O2, R2) can be orthogonal (90 o or 270 o ) to the horizontal direction of the liquid crystal window.
  • the first vector can be parallel to a vertical direction of the liquid crystal window and the second vector can be orthogonal to the vertical direction of the liquid crystal window.
  • the first vector can be at about 45 degrees relative to a horizontal direction of the liquid crystal window (45 o or 315 o ) and the second vector can be at about -45 degrees to the horizontal direction of the liquid crystal window (135 o or 225 o ).
  • the twisted nematic liquid crystal layer 110 has an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d.
  • the first alignment layer 113 has a first alignment direction and the second alignment layer 114 has a second alignment direction orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90 o ⁇ 10 o across the cell gap, e.g., from the first alignment layer to the second alignment layer in the absence of external voltage.
  • the cell gap d of the twisted nematic liquid crystal layer ranges from about 3 ⁇ m to about 30 ⁇ m, such as from about 5 ⁇ m to about 25 ⁇ m, from about 6 ⁇ m to about 20 ⁇ m, or from about 10 ⁇ m to about 15 ⁇ m, including all ranges and subranges therebetween.
  • the first electrode 106 can continuously cover at least 80% of the surface of the first glass substrate 101, such as at least 85%, 90%, 95%, 98%, 99%, or 100% of the first glass substrate.
  • the second electrode 107 can continuously cover at least 80% of the surface of the second glass substrate 102, such as at least 85%, 90%, 95%, 98%, 99%, or 100% of the second glass substrate.
  • the first and/or second electrodes are not patterned or pixelated electrodes, e.g., do not comprise gaps in coverage on their respective glass substrate surfaces.
  • the liquid crystal windows can comprise or consist of a single pixel that is driven by the first and second continuous electrodes.
  • the configurations discussed above with reference to FIG.1A are also applicable to the liquid crystal window of FIG.1B, which can include one or both of third and fourth glass substrates.
  • One or both of the first and second polarizers 108, 109 can comprise an iodine-based polarizer or a dye-based polarizer.
  • the twisted nematic liquid crystal window of this embodiment is transparent in the absence of external voltage (e.g., transmittance > 30%). Voltage applied across the first and second electrodes can alter the light transmission of the liquid crystal window.
  • the liquid crystal window when in a dark state, can have a contrast ratio of greater than 5 for viewing angles up to 80 o relative to the normal viewing direction of the liquid crystal window.
  • the contrast ratio can, for example, be greater than 6, 7, 8, 9, 10, or 20 or greater for larger viewing angles (up to 80 o relative to normal). For a normal viewing angle, the contrast ratio can be even higher, such as 100 or greater.
  • Light transmission can also be tuned in the NT TNLC by varying the applied voltage to account for window location, window orientation, user location, sun position, and the like. For example, the NT TNLC can be switched from the transparent state to a first state by applying first voltage V1 or to a second state by applying second voltage V2.
  • the first state and second state can have different light transmittances along different viewing directions for the window.
  • first light transmittance along an upper viewing direction e.g., +80 o relative to a normal viewing direction
  • second light transmittance along a lower viewing direction
  • the first light transmittance can be higher than the second light transmittance.
  • the NT TNLC can be switched to a third state by applying third voltage V3 or to a fourth state by applying fourth voltage V4.
  • third light transmittance along an upper-right viewing direction (e.g., +80 o relative to a normal viewing direction) can be lower than a fourth light transmittance along a lower-left viewing direction (e.g., -80 o relative to a normal viewing direction).
  • the third light transmittance can be higher than the fourth light transmittance.
  • the window can thus be switched into different states by tuning the applied voltage to provide better light blocking and contrast ratio for a given situation and/or viewing direction.
  • Attorney Docket No. SP22-232PCT [0092]
  • Yet another embodiment of the disclosure comprises a normally dark liquid crystal window comprising two twisted nematic liquid crystal layers.
  • such a liquid crystal window comprises: (a) a first polarizer 108 having a first transmission axis, (b) a first substrate assembly 1S comprising a first glass substrate 101, a first electrode 106, and a first alignment layer 113, (c) an interstitial substrate assembly 3S comprising an interstitial substrate 105, a second electrode 107, a second alignment layer 114, and a third alignment layer 123, (d) a twisted nematic liquid crystal layer 110 disposed between the first and interstitial substrate assemblies, (e) a second substrate assembly 2S comprising a second glass substrate 102 and a fourth alignment layer 124, (f) a second twisted nematic liquid crystal layer 120 disposed between the interstitial substrate assembly and the second substrate assembly, and (g) a second polarizer 109 having a second transmission axis.
  • the first substrate assembly 1S, interstitial substrate assembly 3S, and second substrate assembly 2S are all disposed between the first and second polarizers 108, 109.
  • the first substrate assembly 1S and interstitial substrate assembly 3S are oriented such that the first and second alignment layers 113, 114 face each other and the liquid crystal layer 110 is disposed between these two alignment layers.
  • the second substrate assembly 2S and interstitial substrate assembly 3S are oriented such that the third and fourth alignment layers 123, 124 face each other and the second liquid crystal layer 120 is disposed between these two alignment layers.
  • the interstitial substrate can be replaced with two substrates bonded together, e.g., two single liquid crystal cells can be bonded together rather than separating two liquid crystal layers by a single interstitial substrate.
  • Fabrication of an exemplary liquid crystal window according to this embodiment is discussed in Example 3. The components of the liquid crystal window of this embodiment are listed below in Table VIII: Attorney Docket No. SP22-232PCT Table VIII: Normally Dark Dual TN LC Attorney Docket No. SP22-232PCT [0095]
  • the twisted nematic liquid crystal layer 110 has an extraordinary refractive index ne1, an ordinary refractive index no1, and a cell gap d1.
  • the first alignment layer 113 has a first alignment direction and the second alignment layer 114 has a second alignment direction orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90 o ⁇ 10 o across the cell gap (d1), e.g., from the first alignment layer 113 to the second alignment layer 114 in the absence of external voltage.
  • the second twisted nematic liquid crystal layer 120 has an extraordinary refractive index ne2, an ordinary refractive index no2, and a cell gap d2.
  • the third alignment layer 123 has a third alignment direction R3 and the fourth alignment layer 124 has a fourth alignment direction R4 orthogonal to the third alignment direction such that the twisted nematic liquid crystal rotates 90 o ⁇ 10 o across the cell gap (d2), e.g., from the third alignment layer 123 to the fourth alignment layer 124 in the absence of external voltage.
  • the third alignment direction R3 can be parallel or orthogonal to the second alignment direction R2.
  • R2 and R3 may be at an angle relative to each other that is between 0 and 90 degrees.
  • the first polarizer 108 and the second polarizer 109 have orthogonal transmission axes.
  • the rotation direction of twisted nematic liquid crystal layer 110 and the rotation direction of the second twisted nematic liquid crystal layer are opposite to each other.
  • the rotation direction of twisted nematic liquid crystal layer can be left-handed or right-handed.
  • the handedness of the twisted nematic liquid crystal can be selected by a small pretilt angle along the alignment direction or by a small amount of chiral dopant.
  • the orientation of the first liquid crystal adjacent to the second alignment layer and the orientation of the second liquid crystal adjacent to the third alignment layer are orthogonal, parallel, or at an angle between Attorney Docket No. SP22-232PCT 0 and 90 degrees, in the absence of applied voltage.
  • the cell gap d1 of the first twisted nematic liquid crystal layer and/or the cell gap d2 of the second twisted nematic liquid crystal layer can range from about 3 ⁇ m to about 30 ⁇ m, such as from about 10 ⁇ m to about 25 ⁇ m, or from about 15 ⁇ m to about 20 ⁇ m.
  • the twisted nematic liquid crystal window of this embodiment is dark in the absence of external voltage (e.g., transmittance ⁇ 3%) and transparent when voltage is applied (e.g., transmittance > 30%).
  • a transmittance of normally incident visible light in the dark state is less than 0.5% and/or a transmittance of normally incident visible light in the transparent state is greater than 30%.
  • a transmittance of incident light having a wavelength ⁇ of 550 nm and an incident angle of up to 80 o is less than 1% in the dark state and/or greater than 30% in the transparent state.
  • first and second electrodes 106, 107 it is possible for first and second electrodes 106, 107 to comprise interdigitated electrodes disposed on an interior surface (e.g., second surface 101B) of the first glass substrate 101 or on an interior surface (e.g., first surface 101A) of the second glass substrate 102.
  • first and second polarizers 108, 109 can comprise an iodine-based polarizer or a dye-based polarizer.
  • An additional embodiment of the disclosure comprises a normally transparent liquid crystal window comprising two twisted nematic liquid crystal layers.
  • a liquid crystal window comprises: (a) a first polarizer 108 having a first transmission axis, (b), a first substrate assembly 1S comprising a first glass substrate 101, a first electrode 106, and a first alignment layer 113, (c) an interstitial substrate assembly 3S comprising an interstitial substrate 105, a second electrode 107, a second alignment layer 114, and a third alignment layer 123, (d) a twisted nematic liquid crystal layer 110 disposed between the first and interstitial substrate assemblies, (e) a second substrate assembly 2S comprising a second glass substrate 102 and a fourth alignment layer 124, (f) a second twisted nematic liquid crystal layer 120 disposed between the interstitial substrate assembly and the second substrate assembly, and (g) a second polarizer 109 having a second transmission axis.
  • the first substrate assembly 1S, interstitial substrate assembly 3S, and second substrate assembly 2S are all disposed between the first and second polarizers 108, 109.
  • the first substrate assembly 1S and interstitial substrate assembly 3S are oriented such that the first and second alignment layers 113, 114 face each other and the liquid crystal layer 110 is disposed between these two alignment layers.
  • the second substrate assembly 2S and interstitial substrate assembly 3S are oriented such that the third and fourth alignment layers 123, 124 face each other and the second liquid crystal layer 120 is disposed between these two alignment layers.
  • Fabrication of an exemplary liquid crystal window according to this embodiment is discussed in Example 3.
  • the components of the liquid crystal window of this embodiment are listed below in Table IX: Table IX: Normally Transparent Dual TN LC Attorney Docket No. SP22-232PCT [00102]
  • the twisted nematic liquid crystal layer 110 has an extraordinary refractive index n e1 , an ordinary refractive index n o1 , and a cell gap d1.
  • the first alignment layer 113 has a first alignment direction and the second alignment layer 114 has a second alignment direction orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90 o ⁇ 10 o across the cell gap (d1), e.g., from the first alignment layer 113 to the second alignment layer 114 in the absence of external voltage.
  • the second twisted nematic liquid crystal layer 120 has an extraordinary refractive index ne2, an ordinary refractive index no2, and a cell gap d2.
  • the third alignment layer 123 has a third alignment direction and the fourth alignment layer 124 has a fourth alignment direction orthogonal to the third alignment direction such that the twisted nematic liquid crystal rotates 90 o ⁇ 10 o across the cell gap (d2), e.g., from the third alignment layer 123 to the fourth alignment layer 124 in the absence of external voltage.
  • the first polarizer 108 and the second polarizer 109 have parallel transmission axes.
  • the first retardation Re1 (n e1 -n o1 )*d1 of the twisted nematic Attorney Docket No.
  • the rotation direction of twisted nematic liquid crystal layer 110 and the rotation direction of the second twisted nematic liquid crystal layer are opposite to each other.
  • the birefringence distribution of the first twisted nematic liquid crystal layer 110 and the birefringence distribution of the second twisted nematic liquid crystal layer 120 are orthogonal to each other in the absence of external voltage.
  • the cell gap d1 of the first twisted nematic liquid crystal layer and/or the cell gap d2 of the second twisted nematic liquid crystal layer can range from about 3 ⁇ m to about 30 ⁇ m, such as from about 10 ⁇ m to about 25 ⁇ m, or from about 15 ⁇ m to about 20 ⁇ m.
  • the twisted nematic liquid crystal window of this embodiment is transparent in the absence of external voltage (e.g., transmittance > 30%) and dark when voltage is applied (e.g., transmittance ⁇ 3%).
  • a transmittance of normally incident visible light in the dark state is less than 0.5% and/or a transmittance of normally incident visible light in the transparent state is greater than 30%.
  • a transmittance of incident light having a wavelength ⁇ of 550 nm and an incident angle of up to 80 o is less than 1% in the dark state and/or greater than 30% in the transparent state.
  • first and second electrodes 106, 107 it is possible for first and second electrodes 106, 107 to comprise interdigitated electrodes disposed on an interior surface (e.g., second surface 101B) of the first glass substrate 101 or on an interior surface (e.g., first surface 101A) of the second glass substrate 102.
  • first and second polarizers 108, 109 can comprise an iodine-based polarizer or a dye-based polarizer.
  • each substrate can be independently selected and can be the same or different from other substrates in the liquid crystal window.
  • at least one of the substrates in the liquid crystal window can comprise an optically transparent material.
  • the term “optically transparent” is intended to denote that the component and/or layer has a transmission of greater than about 80% in the visible region of the spectrum ( ⁇ 400-700nm).
  • an exemplary component or layer may have greater than about 85% transmittance in the visible light range, such as greater than about 90%, or greater than about 92%, including all ranges and subranges therebetween.
  • all of the substrates in the liquid crystal window can comprise an optically transparent material.
  • all or some of the substrates in the liquid crystal window can comprise glass sheets.
  • the substrates can have any shape and/or size, such as a rectangle, square, or any other suitable shape, including regular and irregular shapes and shapes with one or more curvilinear edges.
  • the substrates can have a thickness of less than or equal to about 4 mm, for example, ranging from about 0.1 mm to about 4 mm, from about 0.2 mm to about 3 mm, from about 0.3 mm to about 2 mm, from about 0.5 mm to about 1.5 mm, or from about 0.7 mm to about 1 mm, including all ranges and subranges therebetween.
  • the substrates can have a thickness of less than or equal to 0.5 mm, such as 0.4 mm, 0.3 mm, 0.2 mm, 0.1 mm, 0.05 mm, or 0.01 mm, including all ranges and subranges therebetween.
  • the substrates can have a thickness ranging from about 1 mm to about 3 mm, such as from about 1.5 to about 2 mm, including all ranges and subranges therebetween.
  • the substrates in the liquid crystal window may, in some embodiments, comprise the same thickness, or may have different thicknesses.
  • the substrates can comprise any glass known in the art, for example, soda-lime silicate, aluminosilicate, alkali- aluminosilicate, borosilicate, alkaliborosilicate, aluminoborosilicate, alkali- aluminoborosilicate, and other suitable display glasses.
  • the substrates may, in some embodiments, comprise the same glass, or may comprise different glasses.
  • the glass substrates may, in various embodiments, be chemically strengthened and/or thermally tempered.
  • suitable commercially available glasses include EAGLE XG® , Lotus TM , Willow ® , and Gorilla ® glasses from Corning Attorney Docket No. SP22-232PCT Incorporated, to name a few.
  • Chemically strengthened glass for example, may be provided in accordance with U.S. Patent Nos.7,666,511, 4,483,700, and 5,674,790, which are incorporated herein by reference in their entireties.
  • one or more of the substrates can comprise a low emissivity or Low-E glass.
  • Low-E glasses have a coating that can minimize the amount of infrared (IR) and/or ultraviolet (UV) light that passes through the glass.
  • the UV and/or IR transmittance of a Low-E glass can be less than about 5%, such as less than 2%, less than 1%, less than 0.5%, or less than 0.1%, including all ranges and subranges therebetween.
  • the Low-E glass can minimize UV and/or IR light transmission without impacting the transmission of visible light through the glass.
  • the third substrate 103 can comprise a Low-E glass that provides UV and/or IR protection for the first substrate 101 and any underlying liquid crystal layer(s).
  • the fourth substrate 104 can comprise a Low-E glass that provides UV and/or IR protection for the second substrate 102 and any underlying liquid crystal layer(s).
  • Low-E glass When Low-E glass is included in the liquid crystal window, it may be oriented to face the exterior, e.g., the outside of a building or vehicle, to protect the liquid crystal window from undesired incoming radiation.
  • the glass substrates may be chosen from glass sheets produced by a fusion draw process. Without wishing to be bound by theory, it is believed that the fusion draw process can provide glass sheets with a relatively low degree of waviness (or high degree of flatness), which may be beneficial for various liquid crystal applications.
  • An exemplary glass substrate may thus, in certain embodiments, comprise a surface waviness of less than about 100 nm as measured with a contact profilometer, such as about 80 nm or less, about 50 nm or less, about 40 nm or less, or about 30 nm or less, including all ranges and subranges therebetween.
  • At least one of the first and second surfaces 101A, 101B of first glass substrate 101 and/or at least one of the first and second surfaces 102A, 102B of second glass substrates 102 can, in some embodiments, comprise a surface waviness as described above, e.g., of less than about 100 nm.
  • SP22-232PCT surfaces of the third, fourth, and/or interstitial substrates 103, 104, 105 can, in non- limiting embodiments, also comprise a surface waviness of less than about 100 nm.
  • the interstitial substrate 105 if present, as well as any other interstitial substrates that might be present in the liquid crystal window, can comprise a glass material as discussed above. According to other embodiments, the interstitial substrate(s) may comprise a material other than glass, such as plastics. Suitable plastic materials include, but are not limited to, polycarbonates, polyacrylates such as polymethylmethacrylate (PMMA), and polyethyelenes such as polyethylene terephthalate (PET).
  • PMMA polymethylmethacrylate
  • PET polyethylene terephthalate
  • Electrodes can comprise at least one electrode pair, e.g., first and second electrodes 106, 107. Additional electrodes may be present depending on the window configuration and the number of switchable layers. The characteristics and properties of each electrode can be independently selected and can be the same or different from other electrodes in the liquid crystal window.
  • Electrode layers in the liquid crystal window may comprise one or more transparent conductive oxides (TCOs), such as indium tin oxide (ITO), indium zinc oxide (IZO), gallium zinc oxide (GZO), aluminum zinc oxide (AZO), and other like materials.
  • TCOs transparent conductive oxides
  • ITO indium tin oxide
  • IZO indium zinc oxide
  • GZO gallium zinc oxide
  • AZO aluminum zinc oxide
  • the electrode layers may comprise other transparent materials, such as a conductive mesh, e.g., comprising metals such as silver nanowires or other nanomaterials such as graphene or carbon nanotubes.
  • a conductive mesh e.g., comprising metals such as silver nanowires or other nanomaterials such as graphene or carbon nanotubes.
  • Printable conductive ink layers such as ActiveGrid TM from C3Nano Inc. may also be used.
  • the sheet resistance of the electrode layers can range from about 10 ⁇ / ⁇ (ohms/square) to about 1000 ⁇ / ⁇ , such as from about 50 ⁇ / ⁇ to about 900 ⁇ / ⁇ , from about 100 ⁇ / ⁇ to about 800 ⁇ / ⁇ , from about 200 ⁇ / ⁇ to about 700 ⁇ / ⁇ , from about 300 ⁇ / ⁇ to about 600 ⁇ / ⁇ , or from about 400 ⁇ / ⁇ to about 500 ⁇ / ⁇ , including all ranges and subranges therebetween.
  • Electrodes can be fabricated using any technique known in the art, such as vacuum sputtering, film lamination, or printing techniques. Electrodes can be deposited on one or more substrate surfaces to form a layer of material that may or may not comprise a pattern.
  • each electrode layer can, for example, independently range from about 1 nm to about 1000 nm such as from Attorney Docket No. SP22-232PCT about 5 nm to about 500 nm, from about 10 nm to about 300 nm, from about 20 nm to about 200 nm, from about 30 nm to about 150 nm, or from about 50 nm to about 100 nm, including all ranges and subranges therebetween.
  • Liquid Crystal Layers [00116] Liquid crystal windows disclosed herein can include at least one liquid crystal layer, such as twisted nematic liquid crystal layer 110 and second liquid crystal layer 120, as well as any other additional liquid crystal layers that might be present in the window.
  • each liquid crystal layer can be independently selected and can be the same or different from other liquid crystal layers in the liquid crystal window.
  • the liquid crystal layer(s) in the window disclosed herein can comprise a cell gap or cavity filled with liquid crystal material.
  • the thickness of the liquid crystal layer, or the cell gap distance, can be maintained by particle spacers and/or columnar spacers dispersed in the liquid crystal layer.
  • the liquid crystal layers can have a thickness or cell gap of less than or equal to about 0.1 mm, for example, ranging from about 0.001 mm to about 0.05 mm, from about 0.002 mm to about 0.03 mm, from about 0.003 mm to about 0.02 mm, from about 0.004 mm to about 0.01 mm, including all ranges and subranges therebetween. If more than one liquid crystal layer is present in the window, these layers may comprise the same thickness or may have different thicknesses. [00118] Any twisted nematic liquid crystal with positive dielectric anisotropy can be used in the liquid crystal windows disclosed herein.
  • the dielectric anisotropy ('H) can range from about +2 to about +100 @ 1KHz and 20qC and/or Tc can range from 60 o C to 120 o C.
  • the birefringence 2n of the twisted nematic liquid crystal can range from about 0.02 to about 0.3 at 589 nm.
  • the extraordinary refractive index ne can range from about 1.5 to about 1.7 and/or the ordinary refractive index no can range from about 1.4 to about 1.6.
  • the twisted nematic liquid crystal may be operable over a broad range of temperatures, such as from about -40 o C to about 100 o C.
  • Attorney Docket No. SP22-232PCT [00119]
  • the liquid crystal windows disclosed herein can have a retardation value Re ranging from about 0.39 ⁇ m to about 1.26 ⁇ m, or from about 0.47 ⁇ m to about 1.07 ⁇ m for visible light wavelengths ranging from 400-700nm.
  • Alignment Layers [00120] Specific alignment of a liquid crystal layer can, in some embodiments, be improved by coating one or more surfaces of the substrates and/or electrodes with an alignment layer. Alignment layers can comprise a thin film of material having a surface energy and anisotropy promoting the desired orientation for the liquid crystals in direct contact with its surface.
  • Exemplary materials include, but are not limited to, main chain or side chain polyimides, which can be mechanically rubbed to generate layer anisotropy; photosensitive polymers, such as azobenzene-based compounds, which can be exposed to linearly polarized light to generate surface anisotropy; and inorganic thin films, such as silica, which can be deposited using thermal evaporating techniques to form periodic microstructures on the surface.
  • Organic alignment layers promoting vertical or homeotropic orientation of the liquid crystal molecules may be rubbed to create different pretilt angles other than 90 o with respect to the plane of the substrate. The pretilt angle of the liquid crystal molecules with respect to the substrate surface will break the symmetry during switching from vertical orientation and can define an azimuthal direction of liquid crystal switching.
  • Organic alignment layers may be deposited, for example, by spincoating a solution onto a desired surface or using printing techniques. Inorganic alignment layers can be deposited using thermal evaporation techniques. Any alignment layer(s) present in the liquid crystal window can have, for example, a thickness of less than or equal to about 100 nm, for example, ranging from about 1 nm to about 100 nm, from about 5 nm to about 90 nm, from about 10 nm to about 80 nm, from about 20 nm to about 70 nm, from about 30 nm to about 60 nm, or from about 40 nm to about 50 nm, including all ranges and subranges therebetween.
  • the compensation layer can be used in the liquid crystal windows disclosed herein to improve the viewing angle of the transparent state of a ND TNLC and/or the viewing angle of the dark sate of a NT TNLC.
  • the viewing angle is defined by a polar viewing angle and an azimuthal viewing angle.
  • the polar viewing angle is measured from the normal direction of the LC layer, and the azimuthal viewing angle is measured in the plane of the LC layer relative to a chosen direction such as rubbing or alignment direction.
  • a good viewing angle is defined by a contrast of 10 or higher.
  • a non-limiting example of a commercially available compensation layer is a Wide View Film from Fuji Photo Co., which is a discotic liquid crystal polymer film. The optical axis of the film varies along the thickness of the film, as discussed in Hiroyuki Mori et al., Jpn. J. Appl. Phys.36143 (1997).
  • the compensation layer may include a biaxial plate, an A-plate, a C-plate, or a combination of A-plate and C-plate.
  • a biaxial plate has a thickness d and three different refractive indices Nx, Ny, and Nz in the x, y, and z directions, respectively. Its in-plane retardation (Nx-Ny)*d and out-of-plane retardation (Nz- (Nx+Ny)/2)*d can be tuned to compensate the viewing angle dependence of the transmittance for the dark state of a ND TNLC.
  • An A-plate or C-plate each has a thickness d and two different refractive indices such as extraordinary index Ne and ordinary index No.
  • the A-plate has its optic axis oriented in the plane of the compensation layer, while the C-plate has its optic axis oriented orthogonal to the plane of the compensation layer.
  • the liquid crystal windows disclosed herein can comprise at least two polarizers, which can be chosen from iodine-based polarizers and dye-based polarizers.
  • the polarizer may comprise a polyvinyl alcohol (PVA) film that is doped with iodine. This type of polarizer is referred to as H type.
  • the polarizer may comprise a polyvinyl alcohol (PVA) film that is doped with iodine and Attorney Docket No. SP22-232PCT subsequently dehydrated.
  • the polarizer may be more resistant to humidity and heat.
  • the polarizer may, for example, be 3M VikuitiTM KE type polarizer, which comprises iodine doped PVA with unoriented chromophores destroyed by UV bleaching.
  • the KE polarizer has a higher transmittance.
  • the polarizer can also be a dye-based polarizer in some embodiments.
  • Non-limiting exemplary commercially available dye-based polarizers include the Polatechno GHC, VHC, and VHC type polarizers available from Nippon Kayaku (Japan) or High- Temperature Linear Polarizing Film (XP40HT) from Edmund Optics.
  • Liquid crystal windows disclosed herein can include at least one interlayer, for example, if third and/or fourth substrates are present, e.g., as shown in FIG.1B, interlayers may be present between the first substrate 101 and the third substrate 103 and/or between the second substrate 102 and the fourth substrate 104.
  • Interlayers can comprise, in some embodiments, one or more materials chosen from polyvinyl butyral (PVB), polylactic acid, polyurethanes, SentryGlas® and SentryGlas® Plus from DuPont, and other suitable materials.
  • PVB polyvinyl butyral
  • the interlayers if present, can improve the safety of the liquid crystal window, e.g., by holding one or more glass substrates in place in case of breakage.
  • first interlayer 115 can hold the third glass substrate 103 in place in case of breakage and/or second interlayer 116 can hold the fourth glass substrate 104 in place in case of breakage.
  • Other advantages can also include UV and/or IR protection for the first and/or second substrates and underlying liquid crystal layer(s).
  • the UV and/or IR transmittance of the interlayers can be less than 5%, such as less than 2%, less than 1%, less than 0.5%, or less than 0.1%, including all ranges and subranges therebetween. If more than one interlayer is present, they may have the same UV and/or IR transmittance, or different transmittances. For example, referring to FIG.
  • the first interlayer 108 may have a lower UV and/or IR transmittance to protect the remaining liquid crystal window components from UV and/or IR radiation, whereas the second interlayer 109 may have a higher UV and/or IR transmittance because it faces the interior.
  • the fourth substrate 104 faces the exterior, the second interlayer 109 may have a lower UV and/or IR transmittance.
  • Liquid crystal windows can be configured and switched as a single pixel, but it is also possible to configure the electrodes such that the window comprises several pixels, e.g., 2 x 2, 3 x 3, 4 x 4, 5 x 5 pixels, and so forth.
  • the dimensions of each pixel can vary, such as 70 mm x 70 mm or greater, 100 mm x 100 mm or greater, 200 mm x 200 mm or greater, 500 mm x 500 mm or greater, 1000 mm x 1000 mm or greater, and so forth.
  • Each pixel can be individually switched using direct wiring or passive matrix driving methods.
  • the liquid crystal windows disclosed herein can be used in various architectural and transportation applications.
  • the liquid crystal devices can be used as liquid crystal windows that can be included in doors, space partitions, skylights, and windows for buildings, automobiles, and other transportation vehicles such as trains, planes, motorhomes, boats, and the like.
  • Liquid crystal window devices for use in architectural applications can have any desired dimension including, but not limited to 2’ x 4’ (width x height), 3’ x 5’, 5’ x 8’, 6’ x 8’, 7 x10’, 7’ x 12’. Larger and smaller liquid crystal windows are also envisioned and are intended to fall within the scope of this disclosure.
  • the liquid crystal windows disclosed herein can comprise one or more additional components such as a frame or other structural component, a power source, and/or a control device or system.
  • Operation of the liquid crystal windows disclosed herein can comprise switching the windows from one state to another, e.g., switching a ND TNLC from the dark state to the transparent state and back, or switching a NT TNLC from the transparent state to the dark state and back. Switching between states can be achieved by applying voltage to electrodes in electrical contact with the liquid crystal layer(s).
  • the voltage can, for example, be greater than about 1 volt, such as greater than about 2 volts, greater than about 5 volts, greater than about 10 volts, greater than about 20 volts, or greater than about 24 volts, including all ranges and subranges therebetween, e.g., ranging from about 1 volts to about 24 volts.
  • the voltage is less than 5 volts to accommodate thin film transistor (TFT) operation.
  • TFT thin film transistor
  • higher voltage can be used and is believed to improve transmittance in the transparent state or reduce transmittance in the dark state.
  • Voltage can be applied to the electrodes as a pulse having a time period or pulse width ranging from about 1 millisecond to about 200 milliseconds, Attorney Docket No. SP22-232PCT such as from about 5 milliseconds to about 150 milliseconds, from about 10 milliseconds to about 100 milliseconds, or from about 20 milliseconds to about 50 milliseconds.
  • Example 1 Normally dark twisted nematic liquid crystal (ND TNLC) windows were assembled and measured for visible light transmission. Indium tin oxide (ITO) was applied to two 1.1 mm thick glass substrates to form a transparent electrode on one surface of each substrate. A polymer layer was then applied to each transparent electrode by coating with a 1% solution of PI2555 (Dupont) in a thinning solvent to form alignment layers. The alignment layers were rubbed to provide an alignment direction.
  • ITO Indium tin oxide
  • the two substrate assemblies were positioned proximate to each other in parallel with the alignment layers facing each other (inward).
  • the cell was assembled with the alignment direction of the alignment layers rotated 90 o with respect to one another. Spacers were applied between the two substrate assemblies to provide a cell gap of 10 ⁇ m or 18 ⁇ m.
  • the liquid crystal cell was then sealed by Norland optical adhesive NOA 68.
  • the transmission axes of the two polarizers are parallel, such that the first polarizer has a transmission axis perpendicular to the alignment direction of the first alignment layer and the second polarizer has a Attorney Docket No. SP22-232PCT transmission axis parallel to the alignment direction of the second alignment layer.
  • the liquid crystal window was switched from a dark state to a transparent state by applying a bias voltage of about 24 volts to the electrodes, resulting in a reorientation of the liquid crystal molecules from initially parallel to the substrates to perpendicular to the glass substrates.
  • FIG.5 shows the transmittance of the liquid crystal window in the visible light spectrum (400- 700nm) for a 10 ⁇ m and 18 ⁇ m cell gap in both the presence (V ON ) and absence (V OFF ) of voltage.
  • the polar viewing angle is the viewing angle relative to the normal direction of the cell substrate.
  • FIGS.6E-F are plots of the contrast of the liquid crystal window at three visible wavelengths (451 nm, 551 nm, 649 nm) vs. polar viewing angle in the width (0 o ) and length (90 o ) directions of the window, respectively, as derived from FIGS.6A-B (VOFF) and FIGS.6C-D (VON).
  • the contrast at 649 nm is higher than the contrast at 551 nm, which is higher than the contrast at 451 nm.
  • Example 2 Attorney Docket No. SP22-232PCT [00137] Two normally transparent twisted nematic (NT TN) liquid crystal windows with a cell gap of 4.9 ⁇ m were assembled and measured for visible light transmission.
  • the liquid crystal was ZLI-4792 from Merck.
  • the liquid crystal windows were assembled in the same fashion as Example 1, except that the transmission axes of the polarizers were oriented perpendicular to one another, i.e., the first polarizer had a transmission axis parallel to the alignment direction of the first alignment layer and the second polarizer had a transmission axis parallel to the alignment direction of the second alignment layer.
  • One liquid crystal window (A) was fabricated without compensation films and another liquid crystal window (B) included compensation films between the glass substrates and the polarizers.
  • the compensation films were discotic liquid crystal polymer compensation films (Wide View Film from Fuji Photo Co.).
  • the optic axes of the compensation films were oriented perpendicular to each other.
  • the transmission axis of the first polarizer was parallel to the optic axis of the first compensation film, which was parallel to the alignment direction of the first alignment layer.
  • the transmission axis of the second polarizer was parallel to the optic axis of the second compensation film, which was parallel to the alignment direction of the second alignment layer.
  • the alignment directions of the alignment layers are perpendicular to each other, such that the optic axes of the compensation layers are perpendicular to each other, and the transmission axes of the polarizers are also perpendicular to each other.
  • FIG.7 shows the transmittance of the liquid crystal windows in the visible light spectrum (400- 700nm) in both the presence (VON) and absence (VOFF) of voltage.
  • the liquid crystal window without a compensation film (A) had a weighted transmittance (T_D65) of 35% in the transparent state (VOFF) and a transmittance of ⁇ 0.5% in the dark state (VON).
  • the liquid crystal window with a compensation film exhibited an improved weighted transmittance (T_D65) in the transparent state and lower weighted transmittance (T_D65) in the dark state, as well as improved contrast between the VON and VOFF states over a wider range of visible light Attorney Docket No. SP22-232PCT wavelengths.
  • the compensation film can prevent off angle color shift, increase light transmittance in the transparent state, and reduce light transmittance in the dark state caused by residual liquid crystal phase.
  • Example 3 Two dual twisted nematic liquid crystal windows were assembled in the same fashion as Example 1, except that a second TN liquid crystal layer was included in each dual twisted nematic liquid crystal window, similar to the configuration shown in FIG.2.
  • the first and second TN liquid crystal layers were separated by an interstitial substrate.
  • the second liquid crystal layer is passive, i.e., controlling electrodes were not included to switch the second liquid crystal orientation with the application or removal of voltage.
  • the second liquid crystal layer was sandwiched between two alignment layers with alignment directions that were perpendicular to one another.
  • the rotation of the second liquid crystal layer was opposite that of the rotation of the first liquid crystal layer. This was accomplished by orienting the alignment layers such that one alignment layer in the first pair of alignment layers had an alignment direction opposite (180 o ) relative to the alignment direction of an alignment layer in the second pair of alignment layers.
  • the first and second alignment layers orient the first liquid crystal layer and the alignment direction of the first alignment layer is 0 o and the alignment direction of the second alignment layer is +90 o .
  • the third and fourth alignment layers orient the second liquid crystal layer and the alignment direction of the third alignment layer is - 90 o and the alignment direction of the fourth alignment layer is 0 o .
  • a small amount of left-handed chiral dopant can be added to the first liquid crystal layer to make the first liquid crystal to rotate left-handed, while a small amount of right- handed chiral dopant can be added to the second liquid crystal layer to make the second liquid crystal rotated right-handed.
  • Polarizers were applied to the outer surfaces of the glass substrates.
  • FIG.8 shows the transmittance of the liquid crystal windows versus visible light wavelength for normally dark (ND) and normally transparent (NT) dual TN configurations. Both liquid crystal windows have a weighted transmittance (T_D65) Attorney Docket No. SP22-232PCT of 35% in the visible spectrum in the transparent state and a weighted transmittance of ⁇ 1.5% in the dark state.
  • T_D65 weighted transmittance
  • Indium tin oxide (ITO) of 30-40 nm thickness was applied to two Corning Eagle XG ® glass substrates to form a transparent electrode on one surface of each substrate.
  • the glass substrates were 0.5 mm thick and had width and length dimensions of 370 mm x 470 mm.
  • the active (ITO coated) area of the cell was about 350 mm x 450 mm ( ⁇ 90% coverage).
  • the ITO coating was continuous, not patterned or pixelated over the active area.
  • the alignment layers had perpendicular alignment directions of +45 o and -45 o (315 o ) relative to the horizontal axis of the liquid crystal window.
  • the polarizer transmission axes and absorption axes were also perpendicular to each other and at +45 o and -45 o relative to the horizontal axis, respectively.
  • the compensation films were discotic liquid crystal polymer compensation films (Wide View Film from Fuji Photo Co.).
  • the optic axis of each compensation film varies in a plane that contains the film thickness direction and an alignment direction. The normal direction of the plane of the compensation film was parallel to the absorption axis of the corresponding polarizer.
  • the polar angle varies between 0-80 o , while the azimuthal angle varies between 0-360 o .
  • the contrast ratio is calculated as the ratio between the transmittance at 0 volt and the transmittance at another voltage.
  • the alignment layers have perpendicular alignment directions of 0 o and -90 o (270 o ) relative to the horizontal axis of the liquid crystal window.
  • the polarizer transmission axes are also perpendicular to each other and at 0 o and -90 o relative to the horizontal axis.
  • the optic axes of the compensation films are also oriented perpendicular to each other at 0 o and -90 o relative to the horizontal axis.
  • the liquid crystal molecules Upon application of voltage, the liquid crystal molecules are oriented to face downward.
  • the contrast is calculated as the ratio between the transmittance at 0 volt and the transmittance at another voltage.

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Abstract

Disclosed are liquid crystal devices including at least one twisted nematic liquid crystal layer and at least one pair of polarizers. Also disclosed are liquid crystal windows having at least two twisted nematic liquid crystal layers. Methods for operating such liquid crystal windows are also disclosed.

Description

Attorney Docket No. SP22-232PCT LIQUID CRYSTAL WINDOWS COMPRISING AT LEAST ONE TWISTED NEMATIC LIQUID CRYSTAL LAYER AND AT LEAST ONE POLARIZER CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application No.63/425,147 filed November 14, 2022, the content of which is incorporated herein by reference in its entirety. FIELD OF THE DISCLOSURE [0002] The disclosure relates generally to twisted nematic liquid crystal windows, and more particularly to liquid crystal windows comprising at least one twisted nematic liquid crystal layer and at least one pair of polarizers. BACKGROUND [0003] Liquid crystal devices are used in various architectural and transportation applications, such as windows, doors, space partitions, and skylights for buildings and automobiles. Liquid crystal devices can serve as “smart” or tintable windows for many commercial applications. Various liquid crystal materials can be used in smart windows to provide two or more transmission states, such as a dark or opaque state and a light or transparent state. The window can be switched between states by applying or removing voltage. [0004] Twisted nematic liquid crystal (TNLC) devices typically include a pair of polarizers, one on either side of a cell containing liquid crystal that is rotated by 90 degrees from one surface of the cell to another. For a single cell normally transparent (NT) TNLC, which is light transmissive in the absence of voltage, the polarizers are oriented with their transmission axes perpendicular to each other. For a single cell normally dark (ND) TNLC, which is not light transmissive in the absence of voltage, the polarizers are oriented with their transmission axes parallel to each other. [0005] TNLC has been used in display applications. Using the Gooch- Terry transmission curve, the thickness or cell gap of the liquid crystal can be chosen so the transmission of the liquid crystal is zero or as close as possible to zero in the dark state. However, a larger LC cell gap is often not feasible in display applications Attorney Docket No. SP22-232PCT because it results in slower response times, higher driving voltages, and/or increased device thickness and/or weight, which are undesirable for display applications. [0006] Liquid crystal windows can have larger cell gaps and slower response times as compared to display devices and, thus, TNLC may be a suitable candidate for the LC layer in such windows. However, it is desirable for smart liquid crystal windows to provide high contrast ratio between the on and off states. NT TNLC is known to have an undesirably high transmittance in the dark state when viewed from a large viewing angle, such as 40 degrees or greater. ND TNLC is known to have an undesirable appearance of coloration in the dark state. Liquid crystal windows are often viewed from a variety of different angles and, thus, the quality of the dark state over larger viewing angles in terms of low transmittance and wavelength insensitivity can be important. [0007] It would be desirable to provide a TNLC window that has an improved dark state over a wide range of viewing angles. It would also be desirable to provide a TNLC window with a wavelength insensitive dark state. It would further be advantageous to improve the contrast ratio of such TNLC windows for normal and large viewing angles. SUMMARY [0008] The disclosure relates, in various embodiments, to a normally dark liquid crystal window comprising at least one twisted nematic liquid crystal layer and at least two polarizers. The liquid crystal windows can comprise a first polarizer having a first transmission axis; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; and a second polarizer having a second transmission axis; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a dark state in the absence of applied voltage, and the liquid crystal window is in a transparent state when voltage is applied across the first and Attorney Docket No. SP22-232PCT second electrodes; wherein the twisted nematic liquid crystal layer has a retardation Re = (ne-no)*d of greater than or equal to 1.4 Pm, and Re/O ^ 2 for visible light wavelengths ^ from 400 nm to 700 nm, and wherein the first and second transmission axes are parallel to each other. [0009] The disclosure relates, in certain embodiments, to a normally dark liquid crystal window comprising at least one twisted nematic liquid crystal layer, at least two polarizers, and at least one compensation layer. The liquid crystal windows can comprise a first polarizer having a first transmission axis; a first compensation layer; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation layer; and a second polarizer having a second transmission axis; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a dark state in the absence of applied voltage, and the liquid crystal window is in a transparent state when voltage is applied across the first and second electrodes; wherein the twisted nematic liquid crystal layer has a retardation Re = (ne-no)*d ranging from about 0.39 Pm to about 1.26 Pm, or from about 0.47 Pm to about 1.07 Pm, for visible light wavelengths ^ from 400 nm to 700 nm; and wherein the first and second transmission axes are parallel to each other. [0010] The disclosure relates, in additional embodiments, to normally transparent liquid crystal windows comprising at least one twisted nematic liquid crystal layer, at least two polarizers, and at least one compensation layer. The liquid crystal windows can comprise a first polarizer having a first transmission axis; a first compensation layer; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation layer; and a second polarizer Attorney Docket No. SP22-232PCT having a second transmission axis; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a transparent state in the absence of applied voltage, and the liquid crystal window is in a dark state when voltage is applied across the first and second electrodes; and wherein the first and second transmission axes are orthogonal to each other. [0011] The disclosure relates, in some embodiments, to normally transparent liquid crystal windows comprising at least one twisted nematic liquid crystal layer, at least two polarizers, at least one compensation layer, and at least one continuous electrode layer. The liquid crystal windows can comprise a first polarizer having a first absorption axis; a first compensation layer having a first optical axis varying in a first optical plane; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation layer having a second optical axis varying in a second optical plane; and a second polarizer having a second absorption axis; wherein the liquid crystal window comprises vertical and horizontal directions in a viewing plane of the liquid crystal window and a normal viewing direction perpendicular to the viewing plane; wherein the first absorption axis, a first normal direction of the first optical plane, and the first alignment direction are aligned along a first vector; wherein the second absorption axis, a second normal direction of the second optical plane, and the second alignment direction are aligned along a second vector that is orthogonal to the first vector; wherein the first electrode continuously covers at least about 80% of the first glass substrate and the second electrode continuously covers at least about 80% of the second glass substrate; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and is in electrical contact with the first and second electrodes; and wherein the liquid crystal window is in a transparent state in the absence of applied voltage across the first and second electrodes. [0012] The disclosure relates, in various embodiments, to normally transparent liquid crystal windows comprising at least one twisted nematic liquid Attorney Docket No. SP22-232PCT crystal layer comprising a cell gap of greater than 5μm, at least two polarizers, and at least one compensation layer. The liquid crystal windows can comprise a first polarizer having a first absorption axis; a first compensation layer having a first optical axis varying in a first optical plane; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d greater than 5μm; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation layer having a second optical axis varying in a second optical plane; and a second polarizer having a second absorption axis; wherein the first absorption axis, a first normal direction of the first optical plane, and the first alignment direction are aligned along a first vector; wherein the second absorption axis, a second normal direction of the second optical plane, and the second alignment direction are aligned along a second vector that is orthogonal to the first vector; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and is in electrical contact with the first and second electrodes; and wherein the liquid crystal window is in a transparent state in the absence of applied voltage across the first and second electrodes. [0013] The disclosure relates, in further embodiments, to normally dark liquid crystal windows comprising at least two twisted nematic liquid crystal layer and at least two polarizers. The liquid crystal windows can comprise a first polarizer having a first transmission axis; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a first twisted nematic liquid crystal layer having a first extraordinary refractive index ne1, a first ordinary refractive index no1, a first cell gap d1, a first rotation direction X1, a first birefringence distribution B1, and a first retardation Re1 = (ne1-no1)*d1 for visible light wavelengths ^ from 400 nm to 700 nm; a second alignment layer having a second alignment direction; a second electrode; an interstitial glass substrate; a third alignment layer having a third alignment direction; a second twisted nematic liquid crystal layer having a second extraordinary refractive index ne2, a second ordinary refractive index no2, a second cell gap d2, a second rotation direction X2; a second birefringence distribution B2, and a second retardation Re2 = (ne2-no2)*d2 for visible light wavelengths ^ from 400 nm to 700 nm; a fourth alignment layer having a fourth alignment direction; a second glass substrate; and a second polarizer having a second transmission axis; wherein Attorney Docket No. SP22-232PCT the first twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a dark state in the absence of applied voltage, and the liquid crystal window is in a transparent state when voltage is applied across the first and second electrodes; wherein the first twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the second twisted nematic liquid crystal layer is disposed between the third and fourth alignment layers and the third alignment direction is orthogonal to the fourth alignment direction; wherein the first rotation direction X1 is opposite to the second rotation direction X2; wherein the first retardation Re1 is substantially equal to the second retardation Re2; wherein the first and second birefringence distributions are orthogonal to each other in the absence of applied voltage; and wherein the first and second transmission axes are orthogonal to each other. [0014] The disclosure relates, in still further embodiments, to normally transparent liquid crystal windows comprising at least two twisted nematic liquid crystal layers and at least two polarizers. The liquid crystal windows can comprise a first polarizer having a first transmission axis; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a first twisted nematic liquid crystal layer having a first extraordinary refractive index ne1, a first ordinary refractive index no1, a first cell gap d1, a first rotation direction X1, a first birefringence distribution B1, and a first retardation Re1 = (ne1-no1)*d1 for visible light wavelengths ^ from 400 nm to 700 nm; a second alignment layer having a second alignment direction; a second electrode; an interstitial glass substrate; a third alignment layer having a third alignment direction; a second twisted nematic liquid crystal layer having a second extraordinary refractive index ne2, a second ordinary refractive index no2, a second cell gap d2, a second rotation direction X2; a second birefringence distribution B2, and a second retardation Re2 = (ne2-no2)*d2 for visible light wavelengths ^ from 400 nm to 700 nm; a fourth alignment layer having a fourth alignment direction; a second glass substrate; and a second polarizer having a second transmission axis; wherein the first twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a transparent state in the absence of applied voltage, and the liquid crystal window is in a dark state when voltage is applied across the first and second electrodes; wherein the first twisted nematic liquid crystal layer is disposed between the first and Attorney Docket No. SP22-232PCT second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the second twisted nematic liquid crystal layer is disposed between the third and fourth alignment layers and the third alignment direction is orthogonal to the fourth alignment direction; wherein the first rotation direction X1 is opposite to the second rotation direction X2; wherein the first retardation Re1 is substantially equal to the second retardation Re2; wherein the first and second birefringence distributions are orthogonal to each other in the absence of applied voltage; and wherein the first and second transmission axes are parallel to each other. [0015] Additional features and advantages of the disclosure will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments as described herein, including the detailed description which follows, the claims, as well as the appended drawings. [0016] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary and are intended to provide an overview or framework for understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding of the disclosure and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the disclosure and together with the description serve to explain the principles and operations of the various embodiments. BRIEF DESCRIPTION OF THE DRAWINGS [0017] The following detailed description can be further understood when read in conjunction with the following drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. It is to be understood that the figures are not drawn to scale and the size of each depicted component or the relative size of one component to another is not intended to be limiting. [0018] FIGS.1A-B depict cross-sectional views of liquid crystal windows according to various embodiments of the disclosure; [0019] FIG.2 depicts a cross-sectional view of a liquid crystal window according to additional embodiments of the disclosure; Attorney Docket No. SP22-232PCT [0020] FIG.3A-B are schematics depicting the operation of a ND TNLC twisted nematic liquid crystal window in the absence of voltage (dark) and with applied voltage (transparent), respectively; [0021] FIG.4 is a plot depicting the calculated transmittance of a ND TNLC as a function of wavelength for different cell gaps; [0022] FIG.5 is a plot depicting transmittance of a ND TNLC in the visible light spectrum for different cell gaps in the presence and absence of voltage; [0023] FIG.6A-B are plots depicting the normalized transmittance of a ND TNLC at three visible wavelengths vs. polar viewing angle in the width (0o) and length (90o) directions of the window, respectively, in the absence of applied voltage; [0024] FIG.6C-D are plots depicting the normalized transmittance of a ND TNLC at three visible wavelengths vs. polar viewing angle in the width (0o) and length (90o) directions of the window, respectively, in the presence of applied voltage; [0025] FIGS.6E-F are plots of the contrast of the liquid crystal window at three visible wavelengths vs. polar viewing angle in the width (0o) and length (90o) directions of the window, respectively; [0026] FIG.7 is a plot depicting the transmittance of a NT TNLC in the visible light spectrum in the presence and absence of voltage; [0027] FIG.8 is a plot depicting the transmittance of NT and ND dual TNLC in the visible light spectrum in the presence and absence of voltage; and [0028] FIG 9A-F are polar plots depicting the transmittance of a NT TNLC at 550 nm for different applied voltages. DETAILED DESCRIPTION [0029] Disclosed herein are liquid crystal windows comprising: a first polarizer having a first transmission axis; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; and a second polarizer having a second transmission axis; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the twisted nematic liquid Attorney Docket No. SP22-232PCT crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a dark state in the absence of applied voltage, and the liquid crystal window is in a transparent state when voltage is applied across the first and second electrodes; wherein the twisted nematic liquid crystal layer has a retardation Re = (ne-no)*d of greater than or equal to 1.4 Pm, and Re/O ^ 2 for visible light wavelengths ^ from 400 nm to 700 nm, and wherein the first and second transmission axes are parallel to each other. [0030] Also disclosed herein are liquid crystal windows comprising a first polarizer having a first transmission axis; a first compensation layer; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation layer; and a second polarizer having a second transmission axis; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a dark state in the absence of applied voltage, and the liquid crystal window is in a transparent state when voltage is applied across the first and second electrodes; wherein the twisted nematic liquid crystal layer has a retardation Re = (ne-no)*d ranging from about 0.39 Pm to about 1.26 Pm, or from about 0.47 Pm to about 1.07 Pm, for visible light wavelengths ^ from 400 nm to 700 nm; and wherein the first and second transmission axes are parallel to each other. [0031] Additionally disclosed herein are liquid crystal windows comprising a first polarizer having a first transmission axis; a first compensation layer; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation layer; and a second polarizer having a second transmission axis; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the Attorney Docket No. SP22-232PCT second alignment direction; wherein the twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a transparent state in the absence of applied voltage, and the liquid crystal window is in a dark state when voltage is applied across the first and second electrodes; and wherein the first and second transmission axes are orthogonal to each other. [0032] Also disclosed herein are liquid crystal windows comprising a first polarizer having a first absorption axis; a first compensation layer having a first optical axis varying in a first optical plane; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; a second alignment layer having a second alignment direction; a second electrode having a second absorption axis; a second glass substrate; a second compensation layer having a second optical axis varying in a second optical plane; and a second polarizer having a second transmission axis; wherein the liquid crystal window comprises vertical and horizontal directions in a viewing plane of the liquid crystal window and a normal viewing direction perpendicular to the viewing plane; wherein the first absorption axis, a first normal direction of the first optical plane, and the first alignment direction are aligned along a first vector; wherein the second absorption axis, a second normal direction of the second optical plane, and the second alignment direction are aligned along a second vector that is orthogonal to the first vector; wherein the first electrode continuously covers at least about 80% of the first glass substrate and the second electrode continuously covers at least about 80% of the second glass substrate; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and is in electrical contact with the first and second electrodes; and wherein the liquid crystal window is in a transparent state in the absence of applied voltage across the first and second electrodes. [0033] Additionally disclosed herein are liquid crystal windows comprising a first polarizer having a first absorption axis; a first compensation layer having a first optical axis varying in a first optical plane; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d greater than 5μm; a second alignment layer having a second alignment direction; a second electrode; a second glass substrate; a second compensation Attorney Docket No. SP22-232PCT layer having a second optical axis varying in a second optical plane; and a second polarizer having a second absorption axis; wherein the first absorption axis, a first normal direction of the first optical plane, and the first alignment direction are aligned along a first vector; wherein the second absorption axis, a second normal direction of the second optical plane, and the second alignment direction are aligned along a second vector that is orthogonal to the first vector; wherein the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and is in electrical contact with the first and second electrodes; and wherein the liquid crystal window is in a transparent state in the absence of applied voltage across the first and second electrodes. [0034] Further disclosed herein are liquid crystal windows comprising a first polarizer having a first transmission axis; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a first twisted nematic liquid crystal layer having a first extraordinary refractive index ne1, a first ordinary refractive index no1, a first cell gap d1, a first rotation direction X1, a first birefringence distribution B1, and a first retardation Re1 = (ne1-no1)*d1 for visible light wavelengths ^ from 400 nm to 700 nm; a second alignment layer having a second alignment direction; a second electrode; an interstitial glass substrate; a third alignment layer having a third alignment direction; a second twisted nematic liquid crystal layer having a second extraordinary refractive index ne2, a second ordinary refractive index no2, a second cell gap d2, a second rotation direction X2; a second birefringence distribution B2, and a second retardation Re2 = (ne2-no2)*d2 for visible light wavelengths ^ from 400 nm to 700 nm; a fourth alignment layer having a fourth alignment direction; a second glass substrate; and a second polarizer having a second transmission axis; wherein the first twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a dark state in the absence of applied voltage, and the liquid crystal window is in a transparent state when voltage is applied across the first and second electrodes; wherein the first twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the second twisted nematic liquid crystal layer is disposed between the third and fourth alignment layers and the third alignment direction is orthogonal to the fourth alignment direction; wherein the first rotation direction X1 is opposite to the second rotation direction X2; wherein the first Attorney Docket No. SP22-232PCT retardation Re1 is substantially equal to the second retardation Re2; wherein the first and second birefringence distributions are orthogonal to each other in the absence of applied voltage; and wherein the first and second transmission axes are orthogonal to each other. [0035] Still further disclosed herein are liquid crystal windows comprising a first polarizer having a first transmission axis; a first glass substrate; a first electrode; a first alignment layer having a first alignment direction; a first twisted nematic liquid crystal layer having a first extraordinary refractive index ne1, a first ordinary refractive index no1, a first cell gap d1, a first rotation direction X1, a first birefringence distribution B1, and a first retardation Re1 = (ne1-no1)*d1 for visible light wavelengths ^ from 400 nm to 700 nm; a second alignment layer having a second alignment direction; a second electrode; an interstitial glass substrate; a third alignment layer having a third alignment direction; a second twisted nematic liquid crystal layer having a second extraordinary refractive index ne2, a second ordinary refractive index no2, a second cell gap d2, a second rotation direction X2; a second birefringence distribution B2, and a second retardation Re2 = (ne2-no2)*d2 for visible light wavelengths ^ from 400 nm to 700 nm; a fourth alignment layer having a fourth alignment direction; a second glass substrate; and a second polarizer having a second transmission axis; wherein the first twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a transparent state in the absence of applied voltage, and the liquid crystal window is in a dark state when voltage is applied across the first and second electrodes; wherein the first twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; wherein the second twisted nematic liquid crystal layer is disposed between the third and fourth alignment layers and the third alignment direction is orthogonal to the fourth alignment direction; wherein the first rotation direction X1 is opposite to the second rotation direction X2; wherein the first retardation Re1 is substantially equal to the second retardation Re2; wherein the first and second birefringence distributions are orthogonal to each other in the absence of applied voltage; and wherein the first and second transmission axes are parallel to each other. Attorney Docket No. SP22-232PCT Liquid Crystal Windows [0036] Embodiments of the disclosure will now be discussed with reference to FIGS.1-2, which illustrate various aspects of the liquid crystal windows disclosed herein. The following general description is intended to provide an overview of the claimed devices, and various aspects will be more specifically discussed throughout the disclosure with reference to the non-limiting depicted embodiments, these embodiments being interchangeable with one another within the context of the disclosure. [0037] FIGS.1A, 1B, and 2 illustrate cross-sectional views of non-limiting embodiments of liquid crystal windows 100, 100*, and 200, respectively. The liquid crystal windows disclosed herein may have a single cell configuration, e.g., a single liquid crystal layer controlled by a single pair of electrodes, as depicted in FIGS.1A- B. The liquid crystal windows may also comprise two liquid crystal layers, as depicted in FIG.2, or more than two liquid crystal layers (not depicted). [0038] Referring to FIG.1A, liquid crystal window 100 includes first and second glass substrates 101, 102, an electrode pair comprising first and second electrodes 106, 107, and twisted nematic liquid crystal layer 110. First glass substrate 101 comprises a first surface 101A and a second surface 101B. A first electrode 106 is formed on and/or in direct contact with second surface 101B of first glass substrate 101. Similarly, second glass substrate 102 comprises a first surface 102A and a second surface 102B. A second electrode 107 is formed on and/or in direct contact with first surface 102A of second glass substrate 102. The twisted nematic liquid crystal layer 110 is disposed between and in electrical contact with first and second electrodes 106, 107. In some embodiments, the twisted nematic liquid crystal layer 110 is in direct physical contact with first and second electrodes 106, 107. According to various embodiments, the first and second glass substrates 101, 102 and their corresponding electrodes 106, 107 can define a sealed gap or cell that contains the liquid crystal material. Seals s1 can be used to contain the liquid crystal material in the twisted nematic liquid crystal layer 110. [0039] Liquid crystal window 100 can further include a first alignment or orientation layer 113 disposed between first electrode 106 and twisted nematic liquid crystal layer 110 and/or a second alignment or orientation layer 114 disposed between second electrode 107 and twisted nematic liquid crystal layer 110. As Attorney Docket No. SP22-232PCT depicted in FIG.1A, alignment layers 113, 114 can both be present. In other embodiments, only one of alignment layers 113, 114 may be present. A first compensation layer 111 can be formed on and/or in direct contact with first surface 101A of first glass substrate 101. The first compensation layer 111 can be disposed between the first substrate 101 and a first polarizer 108. Similarly, a second compensation layer 112 can be formed on and/or in direct contact with second surface 102B of second glass substrate 102. The second compensation layer 112 can be disposed between the second substrate 102 and a first polarizer 109. [0040] According to various embodiments, a first substrate assembly 1S can comprise the first glass substrate 101, the first electrode 106, and the first alignment layer 113. A second substrate assembly 2S can comprise the second glass substrate 102, the second electrode 107, and the second alignment layer 114. The twisted nematic liquid crystal layer 110 can be disposed between the first and second substrate assemblies 1S, 2S. [0041] Liquid crystal window 100 can be produced, for example, by coating, printing, or otherwise depositing the first electrode layer 106 on the second surface 101B of the first glass substrate 101, and coating, printing, or otherwise depositing the second electrode layer 106 on the first surface 102A of the second glass substrate 102. Alignment layers 113, 114 can be deposited on electrode layers 106, 107, respectively, and rubbed in the desired direction. The substrate assemblies can then be arranged to form a gap, which can be filled with liquid crystal material to form twisted nematic liquid crystal layer 110. In some embodiments, spacers (not illustrated) can be used to maintain the desired cell gap and resulting liquid crystal layer thickness. In some embodiments, the spacers are black. The black spacers minimize the light leakage in the dark state. The liquid crystal material can be sealed in the cell gaps around all edges using any suitable material, such as optically or thermally curable resins, to form seals s1. First compensation layer 111 and first polarizer 108 can be formed and/or deposited on first surface 101A of first glass substrate 101, and second compensation layer 112 and second polarizer 109 can be formed and/or deposited on second surface 102B of second glass substrate 102. [0042] FIG.1B illustrates a non-limiting configuration for a liquid crystal window 100* further comprising third and/or fourth substrates 103, 104. Third substrate 103 comprises a first surface 103A and a second surface 103B. Fourth Attorney Docket No. SP22-232PCT substrate 104 comprises a first surface 104A and a second surface 104B. Third and fourth substrates 103, 104 can be attached or laminated to first and second substrates 101, 102, respectively, by first and second interlayers 115, 116, respectively. According to various embodiments, first and third substrates 101, 103 can define a first cell gap 117, which can be sealed with seals s2 and may contain at least one insulating gas. Similarly, second and fourth substrates 102, 104 can define a second cell gap 118, which can be sealed with seals s2 and may contain at least one insulating gas. [0043] Cell gaps 117, 118 can be filled with air, an inert gas, or a mixture thereof. Suitable inert gases include, but are not limited to, argon, krypton, xenon, and combinations thereof. Mixtures of inert gases or mixtures of one or more inert gases with air can also be used. Exemplary non-limiting inert gas mixtures include 90/10 or 95/5 argon/air, 95/5 krypton/air, or 22/66/12 argon/krypton/air mixtures. Other ratios of inert gases or inert gases and air can also be used depending on the desired thermal performance and/or end use of the liquid crystal window. [0044] Although FIG.1B depicts a liquid crystal window 100* comprising both a third and a fourth substrate, it is possible for the liquid crystal window 100* to comprise only one of such substrates, for instance, second surface 103B of third substrate 103 can be attached to first surface 101A of the first glass substrate 101 by first interlayer 115 and a fourth substrate may not be present. Alternatively, first surface 104A of fourth substrate 104 can be attached to the second surface 102B of the second glass substrate 102 by second interlayer 116 and the third substrate may not be present. Additionally, while FIG.1B depicts a liquid crystal window 100* comprising both a first cell gap 117 and a second cell gap 118, it is possible for the liquid crystal window 100* to comprise no cell gaps or only one of such cell gaps. For instance, first and third substrates 101, 103 may be directly laminated to one another without a first cell gap 117 and/or second and fourth substrates 102, 104 may be directly laminated to one another without a second cell gap 118. [0045] The liquid crystal window 100* depicted in FIG.1B may be advantageous from a safety standpoint. If the third substrate 103 is broken or damaged, the first interlayer 115 can hold any broken pieces in place. Similarly, if the fourth substrate 104 is broken or damaged, the second interlayer 116 can hold it in place. The liquid crystal window 100* depicted in FIG.1B may also be advantageous from a thermal efficiency standpoint as the insulating gas present in Attorney Docket No. SP22-232PCT the first and/or second cell gaps 117, 118 can reduce thermal transfer across the window layers and thus improve the overall thermal rating of the window 100*. Additional advantages can also include protection from ultraviolet (UV) and/or infrared radiation. At least one of the third or fourth substrate 103, 104 can comprise a low emissivity glass or can comprise a coating that reduces the amount of infrared and ultraviolet light that passes through the substrate. The interlayer can also be used to reduce UV transmittance. By way of non-limiting example, liquid crystal window 100* can be oriented such that third substrate 103 is the outermost substrate facing the exterior, e.g., outside of a building or vehicle, and fourth substrate 104 is the innermost substrate and faces the interior, e.g., inside of a building or vehicle. In this case, third substrate 103 and/or first interlayer 115 can provide UV and/or infrared blocking properties for light L incident upon the liquid crystal window 100*. Of course, the reverse orientation is also possible, in which case the fourth substrate 104 and/or second interlayer 116 can provide UV and/or infrared light blocking. [0046] The liquid crystal devices disclosed herein can, in some embodiments, include more than one switchable layer, such as an additional liquid crystal layer. For instance, referring to FIG.2, liquid crystal window 200 can further include an interstitial substrate 105 disposed between the first and second glass substrates 101, 102. The interstitial substrate 105 may comprise glass, similar to the first and second substrates 101, 102, or may comprise any other suitable transparent material, such as plastic. While FIG.2 depicts a single-cell configuration with an interstitial substrate, it is also possible to use a traditional double-cell configuration, e.g., two side-by-side single cells comprising four substrates (two substrates per cell) instead of two substrates separated by a single interstitial substrate as shown in FIG. 2. [0047] Liquid crystal window 200 can include twisted nematic liquid crystal layer 110, which is disposed between the first glass substrate 101 and the interstitial substrate 105, and a second or additional twisted nematic liquid crystal layer 120, which is disposed between the second glass substrate 102 and the interstitial substrate 105. The rotation direction of the first liquid crystal layer 110 can be the opposite of the rotation direction of the second liquid crystal layer 120, as discussed in more detail below. Similar to FIGS.1A-B, twisted nematic liquid crystal layer 110 can be disposed between first and second alignment layers 113, 114. First and second electrodes 106, 107 can be used to apply voltage to the twisted nematic Attorney Docket No. SP22-232PCT liquid crystal layer 110. The second twisted nematic liquid crystal layer 120 can be disposed between third and fourth alignment layers 123, 124. First polarizer 108 is formed or deposited on first surface 101A of first substrate 101 and second polarizer 109 is formed or deposited on second surface 102B of second substrate 102. [0048] According to various embodiments, a first substrate assembly 1S can comprise the first glass substrate 101, the first electrode 106, and the first alignment layer 113. A second substrate assembly 2S’ can comprise the second glass substrate 102, and the fourth alignment layer 124. An interstitial substrate assembly 103 can comprise the interstitial substrate 105, the second electrode 107, the second alignment layer 114, and the third alignment layer 123. The twisted nematic liquid crystal layer 110 can be disposed between the first substrate assembly 1S and the interstitial substrate assembly 3S. The additional liquid crystal layer 120 can be disposed between the interstitial substrate assembly 3S and the second substrate assembly 2S’. [0049] It is to be understood that the scope of the disclosure is not limited solely to the embodiments depicted in FIGS.1-2. The liquid crystal windows disclosed herein can comprise additional layers and/or substrates with different configurations or combinations of the depicted embodiments. Various embodiments of the liquid crystal windows disclosed herein will now be discussed in more detail. For orientation purposes, a liquid crystal window is defined from the viewpoint of a user standing in front of the window. The liquid crystal window, in some embodiments, comprises an upper edge, lower edge, left edge, and right edge and may, for example, be divided into an upper left, upper right, lower left, and lower right quadrant. An upper direction of the window is defined from the lower edge to the upper edge of the window. A lower direction of the window is defined from the upper edge to the lower edge of the window. Upper and lower directions are vertical (or length) directions. The vertical direction can be perpendicular to a horizontal (or width) direction of the window, which is defined from the left edge to the right edge (right direction) or vice versa (left direction). A normal direction of the liquid crystal window can be defined as a direction perpendicular to the plane of the liquid window. Embodiments [0050] A first non-limiting embodiment of the disclosure comprises a normally dark single-cell twisted nematic liquid crystal window with a retardation Re Attorney Docket No. SP22-232PCT value of greater than or equal to 1.4 Pm, and Re/O ^ for visible light wavelengths (400-700nm). Referring to FIG.1A, such a liquid crystal window comprises: (a) a first polarizer 108 having a first transmission axis, (b), a first substrate assembly 1S comprising a first glass substrate 101, a first electrode 106, and a first alignment layer 113, (c) a second polarizer 109 having a second transmission axis, (d) a second substrate assembly 2S comprising a second glass substrate 102, a second electrode 107, and a second alignment layer 114, and (d) a twisted nematic liquid crystal layer 110 disposed between the first and second substrate assemblies. The first and second substrate assemblies 1S, 2S are disposed between the first and second polarizers 108, 109. The first and second substrate assemblies 1S, 2S are oriented such that the first and second alignment layers 113, 114 face each other and the liquid crystal layer 110 is disposed between these two alignment layers. Compensation layers 111, 112 may or may not be present in this embodiment. [0051] Fabrication of an exemplary liquid crystal window according to this embodiment is discussed in Example 1. The components of the liquid crystal window of this embodiment are listed below in Table I: Table I: Normally Dark Single TN LC
Figure imgf000019_0001
Attorney Docket No. SP22-232PCT
Figure imgf000020_0001
[0052] The first polarizer 108 and the second polarizer 109 have parallel transmission axes. The twisted nematic liquid crystal layer 110 has an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d. The first alignment layer 113 has a first alignment (or rubbing) direction R1 and the second alignment layer 114 has a second alignment (or rubbing) direction R2 orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90o ± 10o across the cell gap (d), e.g., from the first alignment layer to the second alignment layer in the absence of external voltage. The retardation Re of the twisted nematic liquid crystal layer (ne-no)*d is greater than or equal to 1.4 Pm, and Re/O^ 2 for wavelengths ^ in the visible spectrum (~400-700 nm). According to various embodiments, the cell gap d of the twisted nematic liquid crystal layer ranges from about 3 μm to about 30 μm, such as from about 10 μm to about 25 μm, or from about 15 μm to about 20 μm. According to various embodiments, the transmission axis T1 of the first polarizer and the first alignment direction R1 can be parallel or orthogonal to each other. In alternative embodiments, T1 and R1 can be at an angle relative to each other that is between 0 and 90 degrees. [0053] The twisted nematic liquid crystal window of this embodiment is dark in the absence of external voltage (e.g., transmittance < 3%) and transparent when voltage is applied (e.g., transmittance > 30%). In certain embodiments, a transmittance of normally incident visible light in the dark state is less than 0.5%. According to additional embodiments, a transmittance of incident light having a wavelength ^ of 550 nm and an incident angle of up to 80o is less than 1% in the dark state and/or a transmittance of incident light having a wavelength ^ of 500 nm and an incident angle of up to 80o is greater than 30% in the transparent state. Attorney Docket No. SP22-232PCT [0054] The configurations discussed above with reference to FIG.1A are also applicable to the liquid crystal window of FIG.1B, which can include one or both of third and fourth glass substrates. Additionally, while FIGS.1A-B depict liquid crystal layer 110 disposed between first and second electrodes 106, 107, it is possible for first and second electrodes 106, 107 to comprise interdigitated electrodes disposed on an interior surface (e.g., second surface 101B) of the first glass substrate 101 or on an interior surface (e.g., first surface 101A) of the second glass substrate 102. [0055] One or both of the first and second polarizers 108, 109 can comprise an iodine-based polarizer or a dye-based polarizer. Liquid crystal windows often undergo one or more lamination processes at elevated temperatures, e.g., about 100oC to about 140oC for about 10 to about 40 minutes, such as from about 20 to about 30 minutes. As such, in some embodiments, dye-based polarizers may be advantageous because they are more thermally durable at higher temperatures. [0056] FIGS.3A-B depict the operation of a normally dark twisted nematic liquid crystal layer. As used herein, the terms normally dark or normally opaque are used to refer to liquid crystal windows that do not transmit or have minimal transmission of visible light in the absence of applied voltage, e.g., less than about 3% light transmittance, less than about 2% light transmittance, less than about 1% light transmittance, or less than about 0.5% light transmittance. Normally dark liquid crystal windows transmit light upon the application of voltage. The terms normally light or normally transparent are used to refer to liquid crystal windows that transmit visible light in the absence of applied voltage, e.g., greater than about 30% light transmittance, greater than about 35% light transmittance, greater than about 40% light transmittance, or greater than about 45% light transmittance. [0057] FIG.3A shows the twisted nematic liquid crystal in a dark state, e.g., in the absence of voltage (V=0). The liquid crystal LC disposed between first and second polarizers P1, P2 rotates by 90o ± 10o from one polarizer to the other. The ~90o rotation can be created, e.g., by including alignment or orientation layers A1, A2 on either side of the liquid crystal LC, having alignment (or rubbing) directions that are approximately orthogonal to one another, as discussed in more detail below. As shown in FIG.3A, the polarizers P1, P2 have parallel axes of transmission. Polarizer P1 allows light of one polarization that is parallel to the transmission axis of polarizer P1 to pass through. In the absence of voltage, light Attorney Docket No. SP22-232PCT passing through P1 is blocked by polarizer P2, due to the polarization of the light that is rotated ~90o by the twisted nematic liquid crystal, resulting in a dark state. The alignment direction of alignment layer A2 is approximately orthogonal or parallel to the transmission axis of polarizers P1, P2. When voltage is applied (V>0), as shown in FIG.3B, the twisted nematic liquid crystals are aligned vertically relative to the substrates, and light of one polarization can pass through each of components P1, LC, and P2 to achieve a light or transparent state. [0058] In the absence of voltage, the transmittance of the cell is given by the Gooch-Terry curve described by:
Figure imgf000022_0001
where birefringence is defined by 'n = ne- no, ne is the extraordinary refractive index, no is the ordinary refractive index; d is the cell gap, and O is the wavelength of light. The ratio of retardation (Re) over the wavelength of the liquid crystal is defined by Re/^ = 'n*d/^. [0059] When , with m representing the first, second, third minimum conditions and so forth, T becomes zero, corresponding to a perfectly dark state. However, for a typical liquid crystal display, m = 1 or 2. The first minimum (m = 1) appears when ('n*d)/^ = ^3/2 § 0.866 and the second minimum (m = 2) appears when ('n*d)/^ = ^15/2 § 1.936. In a higher order minimum, the thickness or cell gap (d) of the liquid crystal becomes too large for display applications due to the corresponding slow response time, which is proportional to d2. Larger cell gaps also typically require a higher driving voltage, which is proportional to d. A higher order minimum (e.g., m > 2) twisted nematic liquid crystal is thus rarely considered for a display application. [0060] As such, it is possible to achieve a dark state (T = 0 or T § 0) for only a narrow range of wavelengths in display applications. This is workable in typical display devices that employ only red, green, and blue subpixels. In each subpixel, a color filter array allows only a narrow range of wavelengths to pass through the filter. Cell gap can also be tuned for each subpixel color. Table II below Attorney Docket No. SP22-232PCT shows the ratio of retardation over the wavelength Re/^ value for the first and second minimum conditions and the retardation Re(='n*d) values for three primary wavelengths used in display applications. Table II
Figure imgf000023_0001
[0061] As illustrated in Table II, display devices are typically constrained by Re='n*d < 1.4Pm and Re/^ < 2. Unlike display devices, liquid crystal windows cannot employ color filter arrays because it would significantly reduce light transmittance of the window. [0062] Display applications also require a small cell gap, e.g., less than 5 μm or even thinner. The maximum driving voltage is selected to achieve a maximum contrast for the normal viewing direction, but is directly dependent on cell gap. Larger cell gaps are thus undesirable in display applications. By contrast, for liquid crystal windows, a larger cell gap can improve cell fabrication and lamination yields. Driving voltage can also be tuned in a liquid crystal window to control light transmission along numerous viewing directions, not just the normal viewing direction, because sunlight moves with time, users stand in different locations, window locations vary, window orientations vary, and so forth. [0063] FIG.4 is a graph illustrating the calculated transmittance of a normally dark twisted nematic liquid crystal as a function of wavelength (400-700 nm) at different cell gaps (d) for a birefringence ('n) value of 0.2. As shown in FIG. 4, transmittance in the dark state generally approaches zero over visible light wavelengths as the thickness of the liquid crystal layer (cell gap (d)) increases. For window applications, the solar spectrum weighted transmittance (T_D65) is indicative of the ability of a window to achieve a dark state. Table III below shows calculated T_D65 weighted transmittance as a function of cell gap (d) and 'n*d for a birefringence ('n) = 0.2 Attorney Docket No. SP22-232PCT
Figure imgf000024_0001
[0064] When 'n*d ^ 1.4 Pm, the weighted transmittance T_D65 in the dark state is 1.9% or less. When 'n*d ^ 1.8 Pm, the weighted transmittance T_D65 in the dark state is 1.0% or less. When 'n*d ^ 3.0 Pm, the weighted transmittance T_D65 in the dark state is 0.5% or less. Similar weighted transmittance T_D65 values can be calculated for birefringence 'n = 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, or 0.4. [0065] When Re/O ^ 2 or Re ^ 1.4 Pm, the transmittance is ^ 1.5% for all wavelengths between 400 nm and 700 nm and the transmittance is ^ 1.0% for the wavelength 550 nm. For example, Table III shows that when Re ^ 1.4 Pm, T_D65 < 1.9%. At the longest wavelength (700 nm), Re/^ ^ 1.4/0.7 =2. As such, according to some embodiments, the liquid crystal windows disclosed herein have a retardation value Re='n*d ^ 1.4 and Re/^ ^ 2 for visible light wavelengths from 400-700nm. Unlike liquid crystal display applications, the liquid crystal windows disclosed herein may operate at a higher order minimum, e.g., m = 3, 4, 5, and so forth. [0066] An additional non-limiting embodiment of the disclosure comprises a normally dark single-cell twisted nematic liquid crystal window with at least one compensation layer. Referring to FIG.1A, such a liquid crystal window comprises: (a) a first polarizer 108 having a first transmission axis, (b), a first substrate assembly 1S comprising a first glass substrate 101, a first electrode 106, and a first alignment layer 113, (c) a second polarizer 109 having a second transmission axis, (d) a second substrate assembly 2S comprising a second glass substrate 102, a second electrode 107, and a second alignment layer 114, and (d) a twisted nematic liquid crystal layer 110 disposed between the first and second substrate assemblies. The first and second substrate assemblies 1S, 2S are disposed between the first and second polarizers 108, 109. The first and second substrate assemblies 1S, 2S are oriented such that the first and second alignment layers 113, 114 face each other and the liquid crystal layer 110 is disposed between these two alignment layers. At least one or both of compensation layers 111, 112 is present in this embodiment. Attorney Docket No. SP22-232PCT [0067] Fabrication of an exemplary liquid crystal window according to this embodiment is discussed in Example 1. The components of the liquid crystal window of this embodiment are listed below in Table IV: Table IV: Normally Dark Single TN LC with Compensation Layers
Figure imgf000025_0001
[0068] The first polarizer 108 and the second polarizer 109 have parallel transmission axes. The twisted nematic liquid crystal layer 110 has an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d. The first alignment layer 113 has a first alignment direction and the second alignment layer 114 has a second alignment direction orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90o ± 10o across the cell gap, e.g., from Attorney Docket No. SP22-232PCT the first alignment layer to the second alignment layer in the absence of external voltage. The retardation Re of the twisted nematic liquid crystal layer (ne-no)*d can range from about 0.39 Pm to about 1.26 Pm, from about 0.47 Pm to about 1.07 Pm, or greater than or equal to 1.4 Pm for a wavelength ^ in the visible spectrum (400- 700 nm). According to various embodiments, the cell gap d of the twisted nematic liquid crystal layer ranges from about 3 μm to about 30 μm, such as from about 10 μm to about 25 μm, or from about 15 μm to 20 μm. According to various embodiments, the transmission axis T1 of the first polarizer and the first alignment direction R1 can be parallel or orthogonal to each other. In alternative embodiments, T1 and R1 can be at an angle relative to each other that is between 0 and 90 degrees. [0069] The twisted nematic liquid crystal window of this embodiment is dark in the absence of external voltage (e.g., transmittance < 3%) and transparent when voltage is applied (e.g., transmittance > 30%). In certain embodiments, a transmittance of normally incident visible light in the dark state is less than 0.5%. According to additional embodiments, a transmittance of incident light having a wavelength ^ of 550 nm and an incident angle of up to 80o is less than 1% in the dark state and/or a transmittance of incident light having a wavelength ^ of 500 nm and an incident angle of up to 80o is greater than 30% in the transparent state. [0070] The configurations discussed above with reference to FIG.1A are also applicable to the liquid crystal window of FIG.1B, which can include one or both of third and fourth glass substrates. Additionally, while FIGS.1A-B depict liquid crystal layer 110 disposed between first and second electrodes 106, 107, it is possible for first and second electrodes 106, 107 to comprise interdigitated electrodes disposed on an interior surface (e.g., second surface 101B) of the first glass substrate 101 or on an interior surface (e.g., first surface 101A) of the second glass substrate 102. One or both of the first and second polarizers 108, 109 can comprise an iodine-based polarizer or a dye-based polarizer. [0071] A further embodiment of the disclosure comprises a normally transparent single-cell twisted nematic liquid crystal window with at least one compensation layer. Referring to FIG.1A, such a liquid crystal window comprises: (a) a first polarizer 108 having a first transmission axis, (b), a first substrate assembly comprising a first glass substrate 101, a first electrode 106, and a first alignment Attorney Docket No. SP22-232PCT layer 113, (c) a second polarizer 109 having a second transmission axis, (d) a second substrate assembly comprising a second glass substrate 102, a second electrode 107, and a second alignment layer 114, and (d) a twisted nematic liquid crystal layer 110 disposed between the first and second substrate assemblies. The first and second substrate assemblies 1S, 2S are disposed between the first and second polarizers 108, 109. The first and second substrate assemblies 1S, 2S are oriented such that the first and second alignment layers face each other and the liquid crystal window is disposed between these two alignment layers. At least one or both of compensation layers 111, 112 is present in this embodiment. The birefringence distribution of the first and/or second compensation layers mimic the birefringence distribution of the liquid crystal when an external voltage is applied across the first and second electrodes. [0072] Fabrication of an exemplary liquid crystal window according to this embodiment is discussed in Example 2. The components of the liquid crystal window of this embodiment are listed below in Table V: Table V: Normally Transparent Single TNLC with Compensation Layers
Figure imgf000027_0001
Attorney Docket No. SP22-232PCT
Figure imgf000028_0001
[See reference: Hiroyuki Mori et al., Jpn. J. Appl. Phys.36143 (1997)] [0073] The first polarizer 108 and the second polarizer 109 have orthogonal transmission axes. According to certain embodiments, the first transmission axis of the first polarizer 108 can be parallel to a horizontal direction of the first and second glass substrates and the second transmission axis of the second polarizer 109 can be orthogonal to the horizontal direction of the first and second glass substrates. In other embodiments, the first transmission axis of the first polarizer 108 can be parallel to a vertical direction of the first and second glass substrates and the second transmission axis of the second polarizer 109 can be orthogonal to the vertical direction of the first and second glass substrates. In these embodiments, polarizers can be utilized more efficiently, because the polarizers are typically fabricated roll-to-roll and the transmission axis of the polarizers is typically orthogonal to the horizontal direction of the roll. According to certain other embodiments, the first transmission axis of the first polarizer 108 can be at about 45 degrees to a horizontal direction of the first and second glass substrates and the second transmission axis of the second polarizer 109 can be at about -45 degrees to the horizontal direction of the first and second glass substrates. In these embodiments, the liquid crystal window may have a more symmetrical viewing angle characteristic between the left and right. [0074] The twisted nematic liquid crystal layer 110 has an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d. The first alignment layer 113 has a first alignment direction and the second alignment layer 114 has a second alignment direction orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90o ± 10o across the cell gap, e.g., from the first alignment layer to the second alignment layer in the absence of external voltage. When voltage is applied to a NT TNLC, the liquid crystal molecules can be aligned in any given direction, such as facing upward, downward, to the left, or to the right, as defined relative to a user standing in front of the liquid crystal window. In a Attorney Docket No. SP22-232PCT window application, certain liquid crystal molecule configurations may be more effective for creating a dark state with higher contrast ratio than others. In some embodiments, when voltage is applied to the NT TNLC to achieve a dark state, the molecules in the central region of the liquid crystal layer are oriented to point downward. This configuration may be effective in blocking light coming in from the top direction of the window, e.g., southern-facing windows in the northern hemisphere and northern-facing windows in the southern hemisphere. In some embodiments, the liquid crystal molecules can be oriented to point upward when voltage is applied. This configuration can be more effective at blocking light in taller buildings when a user mainly looks down through a window. In other embodiments, the liquid crystal molecules can be oriented to point to the right or left when voltage is applied. These configurations can provide improved blocking of light coming from the east and west directions, respectively. [0075] The retardation Re of the twisted nematic liquid crystal layer (ne- no)*d can range from about 0.46 μm to about 0.49 μm for wavelength ^ of 550 nm, or from about 1.05 μm to about 1.08 μm for wavelength ^ of 550 nm . According to various embodiments, the cell gap d of the twisted nematic liquid crystal layer ranges from about 3 μm to about 30 μm, such as from about 5 μm to about 25 μm, from about 6 μm to about 20 μm, or from about 10 μm to about 15 μm, including all ranges and subranges therebetween. [0076] The twisted nematic liquid crystal window of this embodiment is transparent in the absence of external voltage (e.g., transmittance > 30%) and dark when voltage is applied (e.g., transmittance < 3%). In certain embodiments, a transmittance of normally incident visible light in the dark state is less than 0.5%. According to additional embodiments, a transmittance of incident light having a wavelength ^ of 550 nm and an incident angle of up to 80o is less than 3% in the dark state. [0077] The configurations discussed above with reference to FIG.1A are also applicable to the liquid crystal window of FIG.1B, which can include one or both of third and fourth glass substrates. Additionally, while FIGS.1A-B depict liquid crystal layer 110 disposed between first and second electrodes 106, 107, it is possible for first and second electrodes 106, 107 to comprise interdigitated electrodes disposed on an interior surface (e.g., second surface 101B) of the first glass substrate 101 or on an interior surface (e.g., first surface 101A) of the second Attorney Docket No. SP22-232PCT glass substrate 102. One or both of the first and second polarizers 108, 109 can comprise an iodine-based polarizer or a dye-based polarizer. [0078] A further embodiment of the disclosure comprises a normally transparent single-cell twisted nematic liquid crystal window with at least one compensation layer and a liquid crystal cell gap greater than 5 μm. Referring to FIG. 1A, such a liquid crystal window comprises: (a) a first polarizer 108 having a first transmission axis, (b), a first substrate assembly comprising a first glass substrate 101, a first electrode 106, and a first alignment layer 113, (c) a second polarizer 109 having a second transmission axis, (d) a second substrate assembly comprising a second glass substrate 102, a second electrode 107, and a second alignment layer 114, and (d) a twisted nematic liquid crystal layer 110 disposed between the first and second substrate assemblies having a cell gap greater than 5μm. It is to be understood that the absorption axis of a polarizer is orthogonal to its transmission axis. The first and second substrate assemblies 1S, 2S are disposed between the first and second polarizers 108, 109. The first and second substrate assemblies 1S, 2S are oriented such that the first and second alignment layers face each other and the liquid crystal window is disposed between these two alignment layers. Both compensation layers 111, 112 can be present in this embodiment. [0079] The components of the liquid crystal window of this embodiment are listed below in Table VI: Table VI: Normally Transparent Single TNLC with > 5μm Cell Gap
Figure imgf000030_0001
Attorney Docket No. SP22-232PCT
Figure imgf000031_0001
[0080] The first absorption axis Y1, a first normal direction of Plane 1 (along which first optical axis O1 varies), and first alignment direction R1 are parallel to each other, e.g., aligned along a first vector. The second absorption axis Y2, a second normal direction of Plane 2 (along which second optical axis O2 varies), and second alignment direction R2 are parallel to each other, e.g., aligned along a second vector. The first and second vectors are orthogonal to each other, e.g., first polarizer 108 and the second polarizer 109 can have orthogonal absorption axes, first compensation layer 111 and second compensation layer 112 can have orthogonal optical axes, and first alignment layer 113 and second alignment layer 114 can have orthogonal alignment (or rubbing) directions. [0081] According to certain embodiments, the first vector (Y1, O1, R1) can be parallel (0o or 180o) to a horizontal direction of the liquid crystal window and the second vector (Y2, O2, R2) can be orthogonal (90o or 270o) to the horizontal direction of the liquid crystal window. In other embodiments, the first vector can be parallel to a vertical direction of the liquid crystal window and the second vector can be orthogonal to the vertical direction of the liquid crystal window. According to certain other embodiments, the first vector can be at about 45 degrees relative to a horizontal direction of the liquid crystal window (45o or 315o) and the second vector can be at about -45 degrees to the horizontal direction of the liquid crystal window (135o or 225o). Attorney Docket No. SP22-232PCT [0082] The twisted nematic liquid crystal layer 110 has an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d. The first alignment layer 113 has a first alignment direction and the second alignment layer 114 has a second alignment direction orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90o ± 10o across the cell gap, e.g., from the first alignment layer to the second alignment layer in the absence of external voltage. According to various embodiments, the cell gap d of the twisted nematic liquid crystal layer is greater than 5 μm, such as from about 6 μm to about 30 μm, from about 8 μm to about 25 μm, from about 10 μm to about 20 μm, or from about 12 μm to about 15 μm, including all ranges and subranges therebetween. [0083] The twisted nematic liquid crystal window of this embodiment is transparent in the absence of external voltage (e.g., transmittance > 30%). The configurations discussed above with reference to FIG.1A are also applicable to the liquid crystal window of FIG.1B, which can include one or both of third and fourth glass substrates. Additionally, while FIGS.1A-B depict liquid crystal layer 110 disposed between first and second electrodes 106, 107, it is possible for first and second electrodes 106, 107 to comprise interdigitated electrodes disposed on an interior surface (e.g., second surface 101B) of the first glass substrate 101 or on an interior surface (e.g., first surface 101A) of the second glass substrate 102. One or both of the first and second polarizers 108, 109 can comprise an iodine-based polarizer or a dye-based polarizer. [0084] Yet another embodiment of the disclosure comprises a normally transparent single-cell twisted nematic liquid crystal window with at least one compensation layer and at least one continuous electrode. Referring to FIG.1A, such a liquid crystal window comprises: (a) a first polarizer 108 having a first absorption axis, (b), a first substrate assembly comprising a first glass substrate 101, a first electrode 106, and a first alignment layer 113, (c) a second polarizer 109 having a second absorption axis, (d) a second substrate assembly comprising a second glass substrate 102, a second electrode 107, and a second alignment layer 114, and (d) a twisted nematic liquid crystal layer 110 disposed between the first and second substrate assemblies. It is to be understood that the absorption axis of a polarizer is orthogonal to its transmission axis. The first and second substrate assemblies 1S, 2S are disposed between the first and second polarizers 108, 109. The first and second substrate assemblies 1S, 2S are oriented such that the first and Attorney Docket No. SP22-232PCT second alignment layers face each other and the liquid crystal window is disposed between these two alignment layers. Both compensation layers 111, 112 are present in this embodiment. [0085] Fabrication of an exemplary liquid crystal window according to this embodiment is discussed in Example 4. The components of the liquid crystal window of this embodiment are listed below in Table VII: Table VII: Normally Transparent Single TNLC with Continuous Electrodes
Figure imgf000033_0001
[0086] The first absorption axis Y1, a first normal direction of Plane 1 (along which first optical axis O1 varies), and first alignment direction R1 are parallel to each other, e.g., aligned along a first vector. The second absorption axis Y2, a second normal direction of Plane 2 (along which second optical axis O2 varies), and Attorney Docket No. SP22-232PCT second alignment direction R2 are parallel to each other, e.g., aligned along a second vector. The first and second vectors are orthogonal to each other, e.g., first polarizer 108 and the second polarizer 109 have orthogonal absorption axes, first compensation layer 111 and second compensation layer 112 have orthogonal optical axes, and first alignment layer 113 and second alignment layer 114 have orthogonal alignment (or rubbing) directions. [0087] According to certain embodiments, the first vector (Y1, O1, R1) can be parallel (0o or 180o) to a horizontal direction of the liquid crystal window and the second vector (Y2, O2, R2) can be orthogonal (90o or 270o) to the horizontal direction of the liquid crystal window. In other embodiments, the first vector can be parallel to a vertical direction of the liquid crystal window and the second vector can be orthogonal to the vertical direction of the liquid crystal window. According to certain other embodiments, the first vector can be at about 45 degrees relative to a horizontal direction of the liquid crystal window (45o or 315o) and the second vector can be at about -45 degrees to the horizontal direction of the liquid crystal window (135o or 225o). [0088] The twisted nematic liquid crystal layer 110 has an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d. The first alignment layer 113 has a first alignment direction and the second alignment layer 114 has a second alignment direction orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90o ± 10o across the cell gap, e.g., from the first alignment layer to the second alignment layer in the absence of external voltage. According to various embodiments, the cell gap d of the twisted nematic liquid crystal layer ranges from about 3 μm to about 30 μm, such as from about 5 μm to about 25 μm, from about 6 μm to about 20 μm, or from about 10 μm to about 15 μm, including all ranges and subranges therebetween. [0089] According to various embodiments, the first electrode 106 can continuously cover at least 80% of the surface of the first glass substrate 101, such as at least 85%, 90%, 95%, 98%, 99%, or 100% of the first glass substrate. Similarly, the second electrode 107 can continuously cover at least 80% of the surface of the second glass substrate 102, such as at least 85%, 90%, 95%, 98%, 99%, or 100% of the second glass substrate. In various embodiments, the first and/or second electrodes are not patterned or pixelated electrodes, e.g., do not comprise gaps in coverage on their respective glass substrate surfaces. In further Attorney Docket No. SP22-232PCT embodiments, the liquid crystal windows can comprise or consist of a single pixel that is driven by the first and second continuous electrodes. The configurations discussed above with reference to FIG.1A are also applicable to the liquid crystal window of FIG.1B, which can include one or both of third and fourth glass substrates. One or both of the first and second polarizers 108, 109 can comprise an iodine-based polarizer or a dye-based polarizer. [0090] The twisted nematic liquid crystal window of this embodiment is transparent in the absence of external voltage (e.g., transmittance > 30%). Voltage applied across the first and second electrodes can alter the light transmission of the liquid crystal window. In some embodiments, when in a dark state, the liquid crystal window can have a contrast ratio of greater than 5 for viewing angles up to 80o relative to the normal viewing direction of the liquid crystal window. The contrast ratio can, for example, be greater than 6, 7, 8, 9, 10, or 20 or greater for larger viewing angles (up to 80o relative to normal). For a normal viewing angle, the contrast ratio can be even higher, such as 100 or greater. [0091] Light transmission can also be tuned in the NT TNLC by varying the applied voltage to account for window location, window orientation, user location, sun position, and the like. For example, the NT TNLC can be switched from the transparent state to a first state by applying first voltage V1 or to a second state by applying second voltage V2. The first state and second state can have different light transmittances along different viewing directions for the window. In the first state, first light transmittance along an upper viewing direction (e.g., +80o relative to a normal viewing direction) can be lower than a second light transmittance along a lower viewing direction (e.g., -80o relative to a normal viewing direction). In the second state, the first light transmittance can be higher than the second light transmittance. Similarly, the NT TNLC can be switched to a third state by applying third voltage V3 or to a fourth state by applying fourth voltage V4. In the third state, third light transmittance along an upper-right viewing direction (e.g., +80o relative to a normal viewing direction) can be lower than a fourth light transmittance along a lower-left viewing direction (e.g., -80o relative to a normal viewing direction). In the fourth state, the third light transmittance can be higher than the fourth light transmittance. The window can thus be switched into different states by tuning the applied voltage to provide better light blocking and contrast ratio for a given situation and/or viewing direction. Attorney Docket No. SP22-232PCT [0092] Yet another embodiment of the disclosure comprises a normally dark liquid crystal window comprising two twisted nematic liquid crystal layers. Referring to FIG.2, such a liquid crystal window comprises: (a) a first polarizer 108 having a first transmission axis, (b) a first substrate assembly 1S comprising a first glass substrate 101, a first electrode 106, and a first alignment layer 113, (c) an interstitial substrate assembly 3S comprising an interstitial substrate 105, a second electrode 107, a second alignment layer 114, and a third alignment layer 123, (d) a twisted nematic liquid crystal layer 110 disposed between the first and interstitial substrate assemblies, (e) a second substrate assembly 2S comprising a second glass substrate 102 and a fourth alignment layer 124, (f) a second twisted nematic liquid crystal layer 120 disposed between the interstitial substrate assembly and the second substrate assembly, and (g) a second polarizer 109 having a second transmission axis. [0093] The first substrate assembly 1S, interstitial substrate assembly 3S, and second substrate assembly 2S are all disposed between the first and second polarizers 108, 109. The first substrate assembly 1S and interstitial substrate assembly 3S are oriented such that the first and second alignment layers 113, 114 face each other and the liquid crystal layer 110 is disposed between these two alignment layers. The second substrate assembly 2S and interstitial substrate assembly 3S are oriented such that the third and fourth alignment layers 123, 124 face each other and the second liquid crystal layer 120 is disposed between these two alignment layers. Alternatively, although not illustrated the interstitial substrate can be replaced with two substrates bonded together, e.g., two single liquid crystal cells can be bonded together rather than separating two liquid crystal layers by a single interstitial substrate. [0094] Fabrication of an exemplary liquid crystal window according to this embodiment is discussed in Example 3. The components of the liquid crystal window of this embodiment are listed below in Table VIII: Attorney Docket No. SP22-232PCT Table VIII: Normally Dark Dual TN LC
Figure imgf000037_0001
Attorney Docket No. SP22-232PCT
Figure imgf000038_0001
[0095] The twisted nematic liquid crystal layer 110 has an extraordinary refractive index ne1, an ordinary refractive index no1, and a cell gap d1. The first alignment layer 113 has a first alignment direction and the second alignment layer 114 has a second alignment direction orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90o ± 10o across the cell gap (d1), e.g., from the first alignment layer 113 to the second alignment layer 114 in the absence of external voltage. The second twisted nematic liquid crystal layer 120 has an extraordinary refractive index ne2, an ordinary refractive index no2, and a cell gap d2. The third alignment layer 123 has a third alignment direction R3 and the fourth alignment layer 124 has a fourth alignment direction R4 orthogonal to the third alignment direction such that the twisted nematic liquid crystal rotates 90o ± 10o across the cell gap (d2), e.g., from the third alignment layer 123 to the fourth alignment layer 124 in the absence of external voltage. According to various embodiments, the third alignment direction R3 can be parallel or orthogonal to the second alignment direction R2. In alternative embodiments, R2 and R3 may be at an angle relative to each other that is between 0 and 90 degrees. [0096] The first polarizer 108 and the second polarizer 109 have orthogonal transmission axes. The first retardation Re1 = (ne1-no1)*d1 of the twisted nematic liquid crystal layer 110 can be substantially equal to the second retardation Re2 = (ne2-no2)*d2 of the second twisted nematic liquid crystal layer 120, and Re1 § Re2 can range from about 0.39 μm to about 1.26 μm, 1.26 μm to about 6.0 μm, or greater than 6.0 μm at 550 nm. The rotation direction of twisted nematic liquid crystal layer 110 and the rotation direction of the second twisted nematic liquid crystal layer are opposite to each other. The rotation direction of twisted nematic liquid crystal layer can be left-handed or right-handed. The handedness of the twisted nematic liquid crystal can be selected by a small pretilt angle along the alignment direction or by a small amount of chiral dopant. The orientation of the first liquid crystal adjacent to the second alignment layer and the orientation of the second liquid crystal adjacent to the third alignment layer are orthogonal, parallel, or at an angle between Attorney Docket No. SP22-232PCT 0 and 90 degrees, in the absence of applied voltage. According to various embodiments, the cell gap d1 of the first twisted nematic liquid crystal layer and/or the cell gap d2 of the second twisted nematic liquid crystal layer can range from about 3 μm to about 30 μm, such as from about 10 μm to about 25 μm, or from about 15 μm to about 20 μm. [0097] The twisted nematic liquid crystal window of this embodiment is dark in the absence of external voltage (e.g., transmittance < 3%) and transparent when voltage is applied (e.g., transmittance > 30%). In certain embodiments, a transmittance of normally incident visible light in the dark state is less than 0.5% and/or a transmittance of normally incident visible light in the transparent state is greater than 30%. According to additional embodiments, a transmittance of incident light having a wavelength ^ of 550 nm and an incident angle of up to 80o is less than 1% in the dark state and/or greater than 30% in the transparent state. [0098] While FIG.2 depicts liquid crystal layer 110 disposed between first and second electrodes 106, 107, it is possible for first and second electrodes 106, 107 to comprise interdigitated electrodes disposed on an interior surface (e.g., second surface 101B) of the first glass substrate 101 or on an interior surface (e.g., first surface 101A) of the second glass substrate 102. One or both of the first and second polarizers 108, 109 can comprise an iodine-based polarizer or a dye-based polarizer. [0099] An additional embodiment of the disclosure comprises a normally transparent liquid crystal window comprising two twisted nematic liquid crystal layers. Referring to FIG.2, such a liquid crystal window comprises: (a) a first polarizer 108 having a first transmission axis, (b), a first substrate assembly 1S comprising a first glass substrate 101, a first electrode 106, and a first alignment layer 113, (c) an interstitial substrate assembly 3S comprising an interstitial substrate 105, a second electrode 107, a second alignment layer 114, and a third alignment layer 123, (d) a twisted nematic liquid crystal layer 110 disposed between the first and interstitial substrate assemblies, (e) a second substrate assembly 2S comprising a second glass substrate 102 and a fourth alignment layer 124, (f) a second twisted nematic liquid crystal layer 120 disposed between the interstitial substrate assembly and the second substrate assembly, and (g) a second polarizer 109 having a second transmission axis. Attorney Docket No. SP22-232PCT [00100] The first substrate assembly 1S, interstitial substrate assembly 3S, and second substrate assembly 2S are all disposed between the first and second polarizers 108, 109. The first substrate assembly 1S and interstitial substrate assembly 3S are oriented such that the first and second alignment layers 113, 114 face each other and the liquid crystal layer 110 is disposed between these two alignment layers. The second substrate assembly 2S and interstitial substrate assembly 3S are oriented such that the third and fourth alignment layers 123, 124 face each other and the second liquid crystal layer 120 is disposed between these two alignment layers. [00101] Fabrication of an exemplary liquid crystal window according to this embodiment is discussed in Example 3. The components of the liquid crystal window of this embodiment are listed below in Table IX: Table IX: Normally Transparent Dual TN LC
Figure imgf000040_0001
Attorney Docket No. SP22-232PCT
Figure imgf000041_0001
[00102] The twisted nematic liquid crystal layer 110 has an extraordinary refractive index ne1, an ordinary refractive index no1, and a cell gap d1. The first alignment layer 113 has a first alignment direction and the second alignment layer 114 has a second alignment direction orthogonal to the first alignment direction such that the twisted nematic liquid crystal rotates 90o ± 10o across the cell gap (d1), e.g., from the first alignment layer 113 to the second alignment layer 114 in the absence of external voltage. The second twisted nematic liquid crystal layer 120 has an extraordinary refractive index ne2, an ordinary refractive index no2, and a cell gap d2. The third alignment layer 123 has a third alignment direction and the fourth alignment layer 124 has a fourth alignment direction orthogonal to the third alignment direction such that the twisted nematic liquid crystal rotates 90o ± 10o across the cell gap (d2), e.g., from the third alignment layer 123 to the fourth alignment layer 124 in the absence of external voltage. [00103] The first polarizer 108 and the second polarizer 109 have parallel transmission axes. The first retardation Re1 = (ne1-no1)*d1 of the twisted nematic Attorney Docket No. SP22-232PCT liquid crystal layer 110 can be substantially equal to the second retardation Re2 = (ne2-no2)*d2 of the second twisted nematic liquid crystal layer 120, and Re1 § Re2 can range from about 0.39 μm to about 1.26 μm, 1.26 μm to about 6.0 μm, or greater than 6.0 μm at 550 nm. The rotation direction of twisted nematic liquid crystal layer 110 and the rotation direction of the second twisted nematic liquid crystal layer are opposite to each other. The birefringence distribution of the first twisted nematic liquid crystal layer 110 and the birefringence distribution of the second twisted nematic liquid crystal layer 120 are orthogonal to each other in the absence of external voltage. According to various embodiments, the cell gap d1 of the first twisted nematic liquid crystal layer and/or the cell gap d2 of the second twisted nematic liquid crystal layer can range from about 3 μm to about 30 μm, such as from about 10 μm to about 25 μm, or from about 15 μm to about 20 μm. [00104] The twisted nematic liquid crystal window of this embodiment is transparent in the absence of external voltage (e.g., transmittance > 30%) and dark when voltage is applied (e.g., transmittance < 3%). In certain embodiments, a transmittance of normally incident visible light in the dark state is less than 0.5% and/or a transmittance of normally incident visible light in the transparent state is greater than 30%. According to additional embodiments, a transmittance of incident light having a wavelength ^ of 550 nm and an incident angle of up to 80o is less than 1% in the dark state and/or greater than 30% in the transparent state. [00105] While FIG.2 depicts liquid crystal layer 110 disposed between first and second electrodes 106, 107, it is possible for first and second electrodes 106, 107 to comprise interdigitated electrodes disposed on an interior surface (e.g., second surface 101B) of the first glass substrate 101 or on an interior surface (e.g., first surface 101A) of the second glass substrate 102. One or both of the first and second polarizers 108, 109 can comprise an iodine-based polarizer or a dye-based polarizer. Materials Substrates [00106] The following description is intended to apply to any substrates used in the liquid crystal windows disclosed herein, including those discussed above with reference to FIGS.1-2, e.g., the first, second, third, fourth, and/or insterstitial substrates 101, 102, 103, 104, 105, and any other additional substrates, if present. Attorney Docket No. SP22-232PCT The characteristics and properties of each substrate can be independently selected and can be the same or different from other substrates in the liquid crystal window. [00107] According to non-limiting embodiments, at least one of the substrates in the liquid crystal window can comprise an optically transparent material. As used herein, the term “optically transparent” is intended to denote that the component and/or layer has a transmission of greater than about 80% in the visible region of the spectrum (~400-700nm). For instance, an exemplary component or layer may have greater than about 85% transmittance in the visible light range, such as greater than about 90%, or greater than about 92%, including all ranges and subranges therebetween. In certain embodiments, all of the substrates in the liquid crystal window can comprise an optically transparent material. [00108] According to various embodiments, all or some of the substrates in the liquid crystal window can comprise glass sheets. The substrates can have any shape and/or size, such as a rectangle, square, or any other suitable shape, including regular and irregular shapes and shapes with one or more curvilinear edges. According to various embodiments, the substrates can have a thickness of less than or equal to about 4 mm, for example, ranging from about 0.1 mm to about 4 mm, from about 0.2 mm to about 3 mm, from about 0.3 mm to about 2 mm, from about 0.5 mm to about 1.5 mm, or from about 0.7 mm to about 1 mm, including all ranges and subranges therebetween. In certain embodiments, the substrates can have a thickness of less than or equal to 0.5 mm, such as 0.4 mm, 0.3 mm, 0.2 mm, 0.1 mm, 0.05 mm, or 0.01 mm, including all ranges and subranges therebetween. In non-limiting embodiments, the substrates can have a thickness ranging from about 1 mm to about 3 mm, such as from about 1.5 to about 2 mm, including all ranges and subranges therebetween. The substrates in the liquid crystal window may, in some embodiments, comprise the same thickness, or may have different thicknesses. [00109] In various embodiments, the substrates can comprise any glass known in the art, for example, soda-lime silicate, aluminosilicate, alkali- aluminosilicate, borosilicate, alkaliborosilicate, aluminoborosilicate, alkali- aluminoborosilicate, and other suitable display glasses. The substrates may, in some embodiments, comprise the same glass, or may comprise different glasses. The glass substrates may, in various embodiments, be chemically strengthened and/or thermally tempered. Non-limiting examples of suitable commercially available glasses include EAGLE XG® , Lotus TM , Willow ® , and Gorilla ® glasses from Corning Attorney Docket No. SP22-232PCT Incorporated, to name a few. Chemically strengthened glass, for example, may be provided in accordance with U.S. Patent Nos.7,666,511, 4,483,700, and 5,674,790, which are incorporated herein by reference in their entireties. [00110] According to additional embodiments, one or more of the substrates can comprise a low emissivity or Low-E glass. Low-E glasses have a coating that can minimize the amount of infrared (IR) and/or ultraviolet (UV) light that passes through the glass. The UV and/or IR transmittance of a Low-E glass can be less than about 5%, such as less than 2%, less than 1%, less than 0.5%, or less than 0.1%, including all ranges and subranges therebetween. The Low-E glass can minimize UV and/or IR light transmission without impacting the transmission of visible light through the glass. For example, referring to FIG.1B, the third substrate 103 can comprise a Low-E glass that provides UV and/or IR protection for the first substrate 101 and any underlying liquid crystal layer(s). Similarly, the fourth substrate 104 can comprise a Low-E glass that provides UV and/or IR protection for the second substrate 102 and any underlying liquid crystal layer(s). When Low-E glass is included in the liquid crystal window, it may be oriented to face the exterior, e.g., the outside of a building or vehicle, to protect the liquid crystal window from undesired incoming radiation. [00111] According to various embodiments, the glass substrates may be chosen from glass sheets produced by a fusion draw process. Without wishing to be bound by theory, it is believed that the fusion draw process can provide glass sheets with a relatively low degree of waviness (or high degree of flatness), which may be beneficial for various liquid crystal applications. An exemplary glass substrate may thus, in certain embodiments, comprise a surface waviness of less than about 100 nm as measured with a contact profilometer, such as about 80 nm or less, about 50 nm or less, about 40 nm or less, or about 30 nm or less, including all ranges and subranges therebetween. An exemplary standard technique for measuring waviness (0.8~8mm) with a contact profilometer is outlined in SEMI D15-1296 “FPD Glass Substrate Surface Waviness Measurement Method.” With reference to FIGS.1-2, at least one of the first and second surfaces 101A, 101B of first glass substrate 101 and/or at least one of the first and second surfaces 102A, 102B of second glass substrates 102 can, in some embodiments, comprise a surface waviness as described above, e.g., of less than about 100 nm. Similarly, at least one of the Attorney Docket No. SP22-232PCT surfaces of the third, fourth, and/or interstitial substrates 103, 104, 105 can, in non- limiting embodiments, also comprise a surface waviness of less than about 100 nm. [00112] The interstitial substrate 105, if present, as well as any other interstitial substrates that might be present in the liquid crystal window, can comprise a glass material as discussed above. According to other embodiments, the interstitial substrate(s) may comprise a material other than glass, such as plastics. Suitable plastic materials include, but are not limited to, polycarbonates, polyacrylates such as polymethylmethacrylate (PMMA), and polyethyelenes such as polyethylene terephthalate (PET). Electrodes [00113] The liquid crystal windows disclosed herein can comprise at least one electrode pair, e.g., first and second electrodes 106, 107. Additional electrodes may be present depending on the window configuration and the number of switchable layers. The characteristics and properties of each electrode can be independently selected and can be the same or different from other electrodes in the liquid crystal window. [00114] Electrode layers in the liquid crystal window may comprise one or more transparent conductive oxides (TCOs), such as indium tin oxide (ITO), indium zinc oxide (IZO), gallium zinc oxide (GZO), aluminum zinc oxide (AZO), and other like materials. Alternatively, the electrode layers may comprise other transparent materials, such as a conductive mesh, e.g., comprising metals such as silver nanowires or other nanomaterials such as graphene or carbon nanotubes. Printable conductive ink layers such as ActiveGridTM from C3Nano Inc. may also be used. According to various embodiments, the sheet resistance of the electrode layers can range from about 10 ȍ/Ƒ (ohms/square) to about 1000 ȍ/Ƒ, such as from about 50 ȍ/Ƒ to about 900 ȍ/Ƒ, from about 100 ȍ/Ƒ to about 800 ȍ/Ƒ, from about 200 ȍ/Ƒ to about 700 ȍ/Ƒ, from about 300 ȍ/Ƒ to about 600 ȍ/Ƒ, or from about 400 ȍ/Ƒ to about 500 ȍ/Ƒ, including all ranges and subranges therebetween. [00115] Electrodes can be fabricated using any technique known in the art, such as vacuum sputtering, film lamination, or printing techniques. Electrodes can be deposited on one or more substrate surfaces to form a layer of material that may or may not comprise a pattern. The thickness of each electrode layer can, for example, independently range from about 1 nm to about 1000 nm such as from Attorney Docket No. SP22-232PCT about 5 nm to about 500 nm, from about 10 nm to about 300 nm, from about 20 nm to about 200 nm, from about 30 nm to about 150 nm, or from about 50 nm to about 100 nm, including all ranges and subranges therebetween. Liquid Crystal Layers [00116] Liquid crystal windows disclosed herein can include at least one liquid crystal layer, such as twisted nematic liquid crystal layer 110 and second liquid crystal layer 120, as well as any other additional liquid crystal layers that might be present in the window. The characteristics and properties of each liquid crystal layer can be independently selected and can be the same or different from other liquid crystal layers in the liquid crystal window. [00117] According to various embodiments, the liquid crystal layer(s) in the window disclosed herein can comprise a cell gap or cavity filled with liquid crystal material. The thickness of the liquid crystal layer, or the cell gap distance, can be maintained by particle spacers and/or columnar spacers dispersed in the liquid crystal layer. The liquid crystal layers can have a thickness or cell gap of less than or equal to about 0.1 mm, for example, ranging from about 0.001 mm to about 0.05 mm, from about 0.002 mm to about 0.03 mm, from about 0.003 mm to about 0.02 mm, from about 0.004 mm to about 0.01 mm, including all ranges and subranges therebetween. If more than one liquid crystal layer is present in the window, these layers may comprise the same thickness or may have different thicknesses. [00118] Any twisted nematic liquid crystal with positive dielectric anisotropy can be used in the liquid crystal windows disclosed herein. A non-limiting example of a commercially available twisted nematic liquid crystals is HTG-135200-100 from Jiangsu Hecheng Display Technology (HCCH) ('H =+57.2 @ 1KHz, ²n=0.204 @ 589 nm, clearing temperature Tc=97oC). In some embodiments, the dielectric anisotropy ('H) can range from about +2 to about +100 @ 1KHz and 20qC and/or Tc can range from 60oC to 120oC. According to various embodiments, the birefringence ²n of the twisted nematic liquid crystal can range from about 0.02 to about 0.3 at 589 nm. In additional embodiments, the extraordinary refractive index ne can range from about 1.5 to about 1.7 and/or the ordinary refractive index no can range from about 1.4 to about 1.6. The twisted nematic liquid crystal may be operable over a broad range of temperatures, such as from about -40oC to about 100oC. Attorney Docket No. SP22-232PCT [00119] As such, according to some embodiments, the liquid crystal windows disclosed herein have a retardation value Re= 'n*d ^ 1.4 μm and Re/^ ^ 2 for visible light wavelengths from 400-700nm. In additional embodiments, the liquid crystal windows disclosed herein can have a retardation value Re ranging from about 0.39 μm to about 1.26 μm, or from about 0.47 μm to about 1.07 μm for visible light wavelengths ranging from 400-700nm. Alignment Layers [00120] Specific alignment of a liquid crystal layer can, in some embodiments, be improved by coating one or more surfaces of the substrates and/or electrodes with an alignment layer. Alignment layers can comprise a thin film of material having a surface energy and anisotropy promoting the desired orientation for the liquid crystals in direct contact with its surface. Exemplary materials include, but are not limited to, main chain or side chain polyimides, which can be mechanically rubbed to generate layer anisotropy; photosensitive polymers, such as azobenzene-based compounds, which can be exposed to linearly polarized light to generate surface anisotropy; and inorganic thin films, such as silica, which can be deposited using thermal evaporating techniques to form periodic microstructures on the surface. Organic alignment layers promoting vertical or homeotropic orientation of the liquid crystal molecules may be rubbed to create different pretilt angles other than 90o with respect to the plane of the substrate. The pretilt angle of the liquid crystal molecules with respect to the substrate surface will break the symmetry during switching from vertical orientation and can define an azimuthal direction of liquid crystal switching. [00121] Organic alignment layers may be deposited, for example, by spincoating a solution onto a desired surface or using printing techniques. Inorganic alignment layers can be deposited using thermal evaporation techniques. Any alignment layer(s) present in the liquid crystal window can have, for example, a thickness of less than or equal to about 100 nm, for example, ranging from about 1 nm to about 100 nm, from about 5 nm to about 90 nm, from about 10 nm to about 80 nm, from about 20 nm to about 70 nm, from about 30 nm to about 60 nm, or from about 40 nm to about 50 nm, including all ranges and subranges therebetween. Attorney Docket No. SP22-232PCT Compensation Layers [00122] The compensation layer can be used in the liquid crystal windows disclosed herein to improve the viewing angle of the transparent state of a ND TNLC and/or the viewing angle of the dark sate of a NT TNLC. The viewing angle is defined by a polar viewing angle and an azimuthal viewing angle. The polar viewing angle is measured from the normal direction of the LC layer, and the azimuthal viewing angle is measured in the plane of the LC layer relative to a chosen direction such as rubbing or alignment direction. Typically, a good viewing angle is defined by a contrast of 10 or higher. In both the transparent state of a ND TNLC and the dark sate of a NT TNLC, the liquid crystal is oriented vertically in the center of the cell gap, while it is tilted near the alignment layers. [00123] A non-limiting example of a commercially available compensation layer is a Wide View Film from Fuji Photo Co., which is a discotic liquid crystal polymer film. The optical axis of the film varies along the thickness of the film, as discussed in Hiroyuki Mori et al., Jpn. J. Appl. Phys.36143 (1997). [00124] The compensation layer may include a biaxial plate, an A-plate, a C-plate, or a combination of A-plate and C-plate. A biaxial plate has a thickness d and three different refractive indices Nx, Ny, and Nz in the x, y, and z directions, respectively. Its in-plane retardation (Nx-Ny)*d and out-of-plane retardation (Nz- (Nx+Ny)/2)*d can be tuned to compensate the viewing angle dependence of the transmittance for the dark state of a ND TNLC. An A-plate or C-plate each has a thickness d and two different refractive indices such as extraordinary index Ne and ordinary index No. The A-plate has its optic axis oriented in the plane of the compensation layer, while the C-plate has its optic axis oriented orthogonal to the plane of the compensation layer. The retardation of the A-plate and C-plate, defined by (Ne-No)*d can be independently tuned to compensate the viewing angle dependence of the transmittance for the dark state of a ND TNLC. Polarizers [00125] The liquid crystal windows disclosed herein can comprise at least two polarizers, which can be chosen from iodine-based polarizers and dye-based polarizers. For example, the polarizer may comprise a polyvinyl alcohol (PVA) film that is doped with iodine. This type of polarizer is referred to as H type. The polarizer may comprise a polyvinyl alcohol (PVA) film that is doped with iodine and Attorney Docket No. SP22-232PCT subsequently dehydrated. This type of polarizer, referred to as K type, may be more resistant to humidity and heat. The polarizer may, for example, be 3M Vikuiti™ KE type polarizer, which comprises iodine doped PVA with unoriented chromophores destroyed by UV bleaching. The KE polarizer has a higher transmittance. The polarizer can also be a dye-based polarizer in some embodiments. Non-limiting exemplary commercially available dye-based polarizers include the Polatechno GHC, VHC, and VHC type polarizers available from Nippon Kayaku (Japan) or High- Temperature Linear Polarizing Film (XP40HT) from Edmund Optics. Interlayers [00126] Liquid crystal windows disclosed herein can include at least one interlayer, for example, if third and/or fourth substrates are present, e.g., as shown in FIG.1B, interlayers may be present between the first substrate 101 and the third substrate 103 and/or between the second substrate 102 and the fourth substrate 104. Interlayers can comprise, in some embodiments, one or more materials chosen from polyvinyl butyral (PVB), polylactic acid, polyurethanes, SentryGlas® and SentryGlas® Plus from DuPont, and other suitable materials. [00127] The interlayers, if present, can improve the safety of the liquid crystal window, e.g., by holding one or more glass substrates in place in case of breakage. For example, referring to FIG.1B, first interlayer 115 can hold the third glass substrate 103 in place in case of breakage and/or second interlayer 116 can hold the fourth glass substrate 104 in place in case of breakage. Other advantages can also include UV and/or IR protection for the first and/or second substrates and underlying liquid crystal layer(s). According to various embodiments, the UV and/or IR transmittance of the interlayers can be less than 5%, such as less than 2%, less than 1%, less than 0.5%, or less than 0.1%, including all ranges and subranges therebetween. If more than one interlayer is present, they may have the same UV and/or IR transmittance, or different transmittances. For example, referring to FIG. 1B, if the third substrate 103 faces the exterior, e.g., outside of a building or vehicle, the first interlayer 108 may have a lower UV and/or IR transmittance to protect the remaining liquid crystal window components from UV and/or IR radiation, whereas the second interlayer 109 may have a higher UV and/or IR transmittance because it faces the interior. Similarly, if the fourth substrate 104 faces the exterior, the second interlayer 109 may have a lower UV and/or IR transmittance. Attorney Docket No. SP22-232PCT [00128] Liquid crystal windows can be configured and switched as a single pixel, but it is also possible to configure the electrodes such that the window comprises several pixels, e.g., 2 x 2, 3 x 3, 4 x 4, 5 x 5 pixels, and so forth. The dimensions of each pixel can vary, such as 70 mm x 70 mm or greater, 100 mm x 100 mm or greater, 200 mm x 200 mm or greater, 500 mm x 500 mm or greater, 1000 mm x 1000 mm or greater, and so forth. Each pixel can be individually switched using direct wiring or passive matrix driving methods. [00129] The liquid crystal windows disclosed herein can be used in various architectural and transportation applications. For example, the liquid crystal devices can be used as liquid crystal windows that can be included in doors, space partitions, skylights, and windows for buildings, automobiles, and other transportation vehicles such as trains, planes, motorhomes, boats, and the like. Liquid crystal window devices for use in architectural applications can have any desired dimension including, but not limited to 2’ x 4’ (width x height), 3’ x 5’, 5’ x 8’, 6’ x 8’, 7 x10’, 7’ x 12’. Larger and smaller liquid crystal windows are also envisioned and are intended to fall within the scope of this disclosure. Although not illustrated, it is to be understood that the liquid crystal windows disclosed herein can comprise one or more additional components such as a frame or other structural component, a power source, and/or a control device or system. [00130] Operation of the liquid crystal windows disclosed herein can comprise switching the windows from one state to another, e.g., switching a ND TNLC from the dark state to the transparent state and back, or switching a NT TNLC from the transparent state to the dark state and back. Switching between states can be achieved by applying voltage to electrodes in electrical contact with the liquid crystal layer(s). The voltage can, for example, be greater than about 1 volt, such as greater than about 2 volts, greater than about 5 volts, greater than about 10 volts, greater than about 20 volts, or greater than about 24 volts, including all ranges and subranges therebetween, e.g., ranging from about 1 volts to about 24 volts. In a typical display application, the voltage is less than 5 volts to accommodate thin film transistor (TFT) operation. However, in the liquid crystal window application, higher voltage can be used and is believed to improve transmittance in the transparent state or reduce transmittance in the dark state. [00131] Voltage can be applied to the electrodes as a pulse having a time period or pulse width ranging from about 1 millisecond to about 200 milliseconds, Attorney Docket No. SP22-232PCT such as from about 5 milliseconds to about 150 milliseconds, from about 10 milliseconds to about 100 milliseconds, or from about 20 milliseconds to about 50 milliseconds. According to various embodiments, the response time of the TNLC, as defined by the time it takes to transition from one voltage state (e.g., V = 0) to another voltage state (e.g., V ^ 0), and vice versa, is greater than about 20 milliseconds, greater than about 100 milliseconds, or greater than about 200 milliseconds . EXAMPLES [00132] The following examples illustrate non-limiting embodiments of the disclosure and are not intended to be limiting on the scope of the disclosure or claims. Example 1 [00133] Normally dark twisted nematic liquid crystal (ND TNLC) windows were assembled and measured for visible light transmission. Indium tin oxide (ITO) was applied to two 1.1 mm thick glass substrates to form a transparent electrode on one surface of each substrate. A polymer layer was then applied to each transparent electrode by coating with a 1% solution of PI2555 (Dupont) in a thinning solvent to form alignment layers. The alignment layers were rubbed to provide an alignment direction. The two substrate assemblies (substrate/electrode/alignment) were positioned proximate to each other in parallel with the alignment layers facing each other (inward). The cell was assembled with the alignment direction of the alignment layers rotated 90o with respect to one another. Spacers were applied between the two substrate assemblies to provide a cell gap of 10 μm or 18 μm. The cell was filled with a nematic liquid crystal HTG-135200-100 (Jiangsu Hecheng Display Technology (HCCH)), where ǻഎ =+57.2 at 1KHz, ǻn=0.204 at 589 nm, Tc=97oC. The liquid crystal cell was then sealed by Norland optical adhesive NOA 68. Commercial iodine type polarizers were then applied to the outside surfaces of the glass substrates as the outermost layers of the liquid crystal cell. Compensation films can be placed between the substrates and the polarizers but were not used in this example. The transmission axes of the two polarizers are parallel, such that the first polarizer has a transmission axis perpendicular to the alignment direction of the first alignment layer and the second polarizer has a Attorney Docket No. SP22-232PCT transmission axis parallel to the alignment direction of the second alignment layer. [00134] The liquid crystal window was switched from a dark state to a transparent state by applying a bias voltage of about 24 volts to the electrodes, resulting in a reorientation of the liquid crystal molecules from initially parallel to the substrates to perpendicular to the glass substrates. FIG.5 shows the transmittance of the liquid crystal window in the visible light spectrum (400- 700nm) for a 10 μm and 18 μm cell gap in both the presence (VON) and absence (VOFF) of voltage. In the dark state (VOFF), both liquid crystal windows had a transmittance of ^ 1.5% for all wavelengths between 480-700nm, a transmittance of ^ 1.0% at 550nm, and a solar spectrum weighted transmittance (T_D65) of ^ 1.0%. In the transparent state (VON), T_D65 was about 35% for both windows. [00135] FIGS.6A-B are plots of the normalized transmittance of the liquid crystal window (cell gap = 18 μm) at three visible wavelengths (451 nm, 551 nm, 649 nm) vs. polar viewing angle in the width (0o) and length (90o) directions of the window, respectively, in the absence of applied voltage (VOFF). The length (90o) direction is parallel to the transmission axes of the parallel polarizers. FIGS.6C-D are plots of the normalized transmittance of the liquid crystal window (cell gap = 18 μm) at three visible wavelengths (451 nm, 551 nm, 649 nm) vs. polar viewing angle in the width (0o) and length (90o) directions of the window, respectively, with applied voltage (VON, 23 volts). The polar viewing angle is the viewing angle relative to the normal direction of the cell substrate. [00136] FIGS.6E-F are plots of the contrast of the liquid crystal window at three visible wavelengths (451 nm, 551 nm, 649 nm) vs. polar viewing angle in the width (0o) and length (90o) directions of the window, respectively, as derived from FIGS.6A-B (VOFF) and FIGS.6C-D (VON). The contrast at 649 nm is higher than the contrast at 551 nm, which is higher than the contrast at 451 nm. The contrast is higher in the direction that is parallel to the transmission axes of the parallel polarizers (length, 90o) than in the direction that is perpendicular to the transmission axes of the polarizers (width, 0o). Compensation films were not used in this example but could be included to improve the viewing angle of the liquid crystal window in the transparent state if desired. Example 2 Attorney Docket No. SP22-232PCT [00137] Two normally transparent twisted nematic (NT TN) liquid crystal windows with a cell gap of 4.9 μm were assembled and measured for visible light transmission. The liquid crystal was ZLI-4792 from Merck. The liquid crystal windows were assembled in the same fashion as Example 1, except that the transmission axes of the polarizers were oriented perpendicular to one another, i.e., the first polarizer had a transmission axis parallel to the alignment direction of the first alignment layer and the second polarizer had a transmission axis parallel to the alignment direction of the second alignment layer. [00138] One liquid crystal window (A) was fabricated without compensation films and another liquid crystal window (B) included compensation films between the glass substrates and the polarizers. The compensation films were discotic liquid crystal polymer compensation films (Wide View Film from Fuji Photo Co.). The optic axes of the compensation films were oriented perpendicular to each other. As such, the transmission axis of the first polarizer was parallel to the optic axis of the first compensation film, which was parallel to the alignment direction of the first alignment layer. Similarly, the transmission axis of the second polarizer was parallel to the optic axis of the second compensation film, which was parallel to the alignment direction of the second alignment layer. As mentioned previously the alignment directions of the alignment layers are perpendicular to each other, such that the optic axes of the compensation layers are perpendicular to each other, and the transmission axes of the polarizers are also perpendicular to each other. [00139] The liquid crystal windows were switched from a transparent state to a dark state by applying a small bias voltage (10 volts) to the electrodes, resulting in a reorientation of the liquid crystal molecules from initially parallel to the substrates to perpendicular to the glass substrates. FIG.7 shows the transmittance of the liquid crystal windows in the visible light spectrum (400- 700nm) in both the presence (VON) and absence (VOFF) of voltage. The liquid crystal window without a compensation film (A) had a weighted transmittance (T_D65) of 35% in the transparent state (VOFF) and a transmittance of ^ 0.5% in the dark state (VON). The liquid crystal window with a compensation film (B) exhibited an improved weighted transmittance (T_D65) in the transparent state and lower weighted transmittance (T_D65) in the dark state, as well as improved contrast between the VON and VOFF states over a wider range of visible light Attorney Docket No. SP22-232PCT wavelengths. The compensation film can prevent off angle color shift, increase light transmittance in the transparent state, and reduce light transmittance in the dark state caused by residual liquid crystal phase. Example 3 [00140] Two dual twisted nematic liquid crystal windows were assembled in the same fashion as Example 1, except that a second TN liquid crystal layer was included in each dual twisted nematic liquid crystal window, similar to the configuration shown in FIG.2. The first and second TN liquid crystal layers were separated by an interstitial substrate. The second liquid crystal layer is passive, i.e., controlling electrodes were not included to switch the second liquid crystal orientation with the application or removal of voltage. The second liquid crystal layer was sandwiched between two alignment layers with alignment directions that were perpendicular to one another. The rotation of the second liquid crystal layer was opposite that of the rotation of the first liquid crystal layer. This was accomplished by orienting the alignment layers such that one alignment layer in the first pair of alignment layers had an alignment direction opposite (180o) relative to the alignment direction of an alignment layer in the second pair of alignment layers. For example, the first and second alignment layers orient the first liquid crystal layer and the alignment direction of the first alignment layer is 0o and the alignment direction of the second alignment layer is +90o. The third and fourth alignment layers orient the second liquid crystal layer and the alignment direction of the third alignment layer is - 90o and the alignment direction of the fourth alignment layer is 0o. Alternatively, a small amount of left-handed chiral dopant can be added to the first liquid crystal layer to make the first liquid crystal to rotate left-handed, while a small amount of right- handed chiral dopant can be added to the second liquid crystal layer to make the second liquid crystal rotated right-handed. [00141] Polarizers were applied to the outer surfaces of the glass substrates. For a normally dark dual TN liquid crystal window, the transmission axes of the polarizers were perpendicular to one another. For a normally transparent dual TN liquid crystal window, the transmission axes of the polarizers were parallel to one another. FIG.8 shows the transmittance of the liquid crystal windows versus visible light wavelength for normally dark (ND) and normally transparent (NT) dual TN configurations. Both liquid crystal windows have a weighted transmittance (T_D65) Attorney Docket No. SP22-232PCT of 35% in the visible spectrum in the transparent state and a weighted transmittance of ^ 1.5% in the dark state. Example 4 [00142] One normally transparent twisted nematic liquid crystal (NT TNLC) window was assembled in a manner similar to Example 2. The liquid crystal cell had a gap of 6 μm, filled with a nematic liquid crystal having a birefringence of about 0.08 at the wavelength O of 550 nm. 'n*d/O § 0.873 (close to the 1st minimum 0.866) for O = 0.55 Pm. Indium tin oxide (ITO) of 30-40 nm thickness was applied to two Corning Eagle XG® glass substrates to form a transparent electrode on one surface of each substrate. The glass substrates were 0.5 mm thick and had width and length dimensions of 370 mm x 470 mm. The active (ITO coated) area of the cell was about 350 mm x 450 mm (~90% coverage). The ITO coating was continuous, not patterned or pixelated over the active area. [00143] In the liquid crystal cell, the alignment layers had perpendicular alignment directions of +45o and -45o (315o) relative to the horizontal axis of the liquid crystal window. The polarizer transmission axes and absorption axes were also perpendicular to each other and at +45o and -45o relative to the horizontal axis, respectively. The compensation films were discotic liquid crystal polymer compensation films (Wide View Film from Fuji Photo Co.). The optic axis of each compensation film varies in a plane that contains the film thickness direction and an alignment direction. The normal direction of the plane of the compensation film was parallel to the absorption axis of the corresponding polarizer. The normal directions of the planes for the two compensation films were oriented perpendicular to each other at +45o and -45o relative to the horizontal axis. Upon application of voltage, the liquid crystal molecules were oriented to face downward. [00144] The first liquid crystal window was switched from a transparent state to a dark state by applying different voltages to the electrodes. FIGS.9A-F are polar plots of transmittance for a wavelength of 550 nm at voltage (V) = 0, 2, 3, 4, 5, and 6 volts, respectively. Each polar plot shows the transmittance of the liquid crystal window vs. polar angle (T) and azimuthal angle (M). The polar angle varies between 0-80o, while the azimuthal angle varies between 0-360o. The directions (T=0q, M=0q), (T=80q, M=0q), (T=80q, M=90q), (T=80q, M=180q), and (T=0q, Attorney Docket No. SP22-232PCT M=270q) correspond to the normal viewing direction, 80 degrees viewed from the top, 80 degrees viewed from the left, 80 degrees viewed from the bottom, and 80 degrees viewed from the right, respectively. [00145] In the absence of voltage (V = 0), the liquid crystal window had a high transmittance of about 38% at 550 nm. See FIG.9A. When voltage was applied, the transmittance was reduced and could be tuned and lowered along certain directions depending on the applied voltage. See FIGS.9B-F. For example, for a southern-facing window, the sun moves from east (left) to south (top) to west (right). To block sunlight from the east (left), the liquid crystal cell could be switched using a voltage V = 2-3 volts to reduce transmittance in that direction. To block sunlight from the southeast or southwest, a switching voltage V = 4-5 volts could be used. Sunlight from the south could be blocked using a switching voltage V = 8 volts or greater. [00146] Tables X and XI show the transmittance (Trans) and contrast ratio (CR) of the first liquid crystal cell, respectively, at three wavelengths O § 450, 550, 650 nm, at (T=0q, M=0q), (T=80q, M=0q), (T=80q, M=90q), (T=80q, M=180q), and (T=0q, M=270q), and when V = 0, 1, 2, 3, 4, 5, 5.5, 5.7, 6, and 8 volts. The contrast ratio is calculated as the ratio between the transmittance at 0 volt and the transmittance at another voltage. Table X: Transmittance
Figure imgf000056_0001
Attorney Docket No. SP22-232PCT Table XI: Contrast Ratio
Figure imgf000057_0001
[00147] In each of the five directions (T=0q, M=0q), (T=80q, M=0q), (T=80q, M=90q), (T=80q, M=180q), and (T=0q, M=270q), a contrast ratio of more than 5 was achieved at polar angle of T=80q at a certain voltage. For example, along the direction (T=0q, M=0q), a contrast ratio of more than 20 was achieved when V ^ 3 volts. Along the direction (T=80q, M=0q), a contrast ratio of more than 10 was achieved when V = 4 volts. Along the direction (T=80q, M=180q), a contrast ratio of more than 5 was achieved when V = 6 or 8 volts. Along the direction (T=80q, M=90q) or (T=80q, M=270q), a contrast ratio of more than 5 was achieved when V = 2 or 3 volts. [00148] [00149] Tables XII and XIII show the transmittance (Trans) and contrast ratio (CR) of a similar liquid crystal cell in which the components are rotated by 45 degrees relative to the first liquid crystal cell, respectively, at three wavelengths O § 450, 550, 650 nm, at (T=80q, M=45q), (T=80q, M=225q), (T=80q, M=135q), and (T=0q, M=315q), and when V = 0, 1, 2, 3, 4, 5, 5.5, 5.7, 6, and 8 volts. The alignment layers have perpendicular alignment directions of 0o and -90o (270o) relative to the horizontal axis of the liquid crystal window. The polarizer transmission axes are also perpendicular to each other and at 0o and -90o relative to the horizontal axis. The optic axes of the compensation films are also oriented perpendicular to each other at 0o and -90o relative to the horizontal axis. Upon application of voltage, the liquid crystal molecules are oriented to face downward. The contrast is calculated as the ratio between the transmittance at 0 volt and the transmittance at another voltage. Attorney Docket No. SP22-232PCT Table XII: Transmittance
Figure imgf000058_0001
Table XIII: Contrast Ratio
Figure imgf000058_0002
[00150] In each of the four directions (T=80q, M=45q), (T=80q, M=225q), (T=80q, M=135q), and (T=0q, M=315q), a contrast ratio of more than 10 was achieved at polar angle of T=80q when the voltage is between 5 and 6 volts, and a contrast ratio of more than 5 was achieved at polar angle of T=80q when the voltage is between 4 and 8 volts. [00151] It will be appreciated that the various disclosed embodiments may involve particular features, elements or steps that are described in connection with that particular embodiment. It will also be appreciated that a particular feature, element or step, although described in relation to one particular embodiment, may be interchanged or combined with alternate embodiments in various non-illustrated combinations or permutations. [00152] While various features, elements or steps of particular embodiments may be disclosed using the transitional phrase “comprising,” it is to be understood that alternative embodiments, including those that may be described Attorney Docket No. SP22-232PCT using the transitional phrases “consisting” or “consisting essentially of,” are implied. Thus, for example, implied alternative embodiments to a device that comprises A+B+C include embodiments where a device consists of A+B+C and embodiments where a device consists essentially of A+B+C. [00153] It will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the spirit and scope of the disclosure. Since modifications combinations, sub- combinations and variations of the disclosed embodiments incorporating the spirit and substance of the disclosure may occur to persons skilled in the art, the disclosure should be construed to include everything within the scope of the appended claims and their equivalents.

Claims

Attorney Docket No. SP22-232PCT WHAT IS CLAIMED IS: 1. A liquid crystal window comprising: (a) a first polarizer having a first transmission axis; (b) a first glass substrate; (c) a first electrode; (d) a first alignment layer having a first alignment direction; (e) a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; (f) a second alignment layer having a second alignment direction; (g) a second electrode; (h) a second glass substrate; and (i) a second polarizer having a second transmission axis; wherein: the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; the twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a dark state in the absence of applied voltage, and the liquid crystal window is in a transparent state when voltage is applied across the first and second electrodes; the twisted nematic liquid crystal layer has a retardation Re = (ne-no)*d of greater than or equal to 1.4 μm for visible light wavelengths ^ from 400 nm to 700 nm; and the first and second transmission axes are parallel to each other. 2. The liquid crystal window of claim 1, further comprising a first compensation layer disposed between the first glass substrate and the first polarizer, a second compensation layer disposed between the second glass substrate and the second polarizer, or both. 3. A liquid crystal window comprising: (a) a first polarizer having a first transmission axis; (b) a first compensation layer; Attorney Docket No. SP22-232PCT (c) a first glass substrate; (d) a first electrode; (e) a first alignment layer having a first alignment direction; (f) a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; (g) a second alignment layer having a second alignment direction; (h) a second electrode; (i) a second glass substrate; (j) a second compensation layer; and (k) a second polarizer having a second transmission axis; wherein: the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; the twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a dark state in the absence of applied voltage, and the liquid crystal window is in a transparent state when voltage is applied across the first and second electrodes; the twisted nematic liquid crystal layer has a retardation Re = (ne-no)*d ranging from about 0.39 μm to about 1.26 μm for visible light wavelengths ^ from 400 nm to 700 nm; and the first and second transmission axes are parallel to each other. 4. The liquid crystal window of any of claims 1-3, wherein a first substrate assembly comprises the first glass substrate, the first electrode, and the first alignment layer, wherein a second substrate assembly comprises the second glass substrate, the second electrode, and the second alignment layer, wherein the first and second substrate assemblies are disposed between the first and second polarizers, and wherein the twisted nematic liquid crystal layer is disposed between the first and second substrate assemblies and in physical contact with the first and second alignment layers. Attorney Docket No. SP22-232PCT 5. The liquid crystal window of any of claims 1-4, wherein the first and second electrodes comprise interdigitated electrodes disposed on an interior surface of the first glass substrate or on an interior surface of the second glass substrate. 6. The liquid crystal window of any of claims 1-5, further comprising a third glass substrate and a first interlayer disposed between the first glass substrate and the third glass substrate, a fourth glass substrate and a second interlayer disposed between the second glass substrate and the fourth glass substrate, or both. 7. The liquid crystal window of any of claims 1-6, wherein the cell gap d of the twisted nematic liquid crystal layer ranges from about 3 μm to about 30 μm. 8. The liquid crystal window of any of claims 1-7, wherein one or both of the first and second polarizers are independently chosen from iodine-based polarizers and dye-based polarizers. 9. The liquid crystal window of any of claims 1-8, wherein a transmittance of normally incident visible light in the dark state is less than 0.5%. 10. The liquid crystal window of any of claims 1-9, wherein a transmittance of normally incident visible light in the transparent state is greater than 30%. 11. The liquid crystal window of any of claims 1-10, wherein a transmittance of incident light having a wavelength ^ of 550 nm and an incident angle of up to 80o is less than 1% in the dark state. 12. The liquid crystal window of any of claims 1-11, wherein a transmittance of incident light having a wavelength ^ of 500 nm and an incident angle of up to 80o is greater than 30% in the transparent state. 13. A method for switching the liquid crystal window of any of claims 1-12 from a dark state to a transparent state, the method comprising applying voltage to the first and second electrodes, the voltage ranging from about 10 volts to about 24 volts. Attorney Docket No. SP22-232PCT 14. The method of claim 13, wherein a response time of the liquid crystal window for switching from the dark state to the transparent state is greater than about 100 milliseconds. 15. A liquid crystal window comprising: (a) a first polarizer having a first transmission axis; (b) a first compensation layer; (c) a first glass substrate; (d) a first electrode; (e) a first alignment layer having a first alignment direction; (f) a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; (g) a second alignment layer having a second alignment direction; (h) a second electrode; (i) a second glass substrate; (j) a second compensation layer; and (k) a second polarizer having a second transmission axis; wherein: the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; the twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a transparent state in the absence of applied voltage, and the liquid crystal window is in a dark state when voltage is applied across the first and second electrodes; and the first and second transmission axes are orthogonal to each other. 16. The liquid crystal window of claim 15, wherein the twisted nematic liquid crystal layer has a retardation Re = (ne-no)*d ranging from about 0.46 μm to about 0.49 μm for a wavelength ^, or from about 1.05 μm to about 1.08 μm for wavelength ^ of 550 nm. 17. The liquid crystal window of claim 15 or 16, wherein a first substrate assembly comprises the first glass substrate, the first electrode, and the first alignment layer, Attorney Docket No. SP22-232PCT wherein a second substrate assembly comprises the second glass substrate, the second electrode, and the second alignment layer, wherein the first and second substrate assemblies are disposed between the first and second polarizers, and wherein the twisted nematic liquid crystal layer is disposed between the first and second substrate assemblies and in physical contact with the first and second alignment layers. 18. The liquid crystal window of any of claims 15-17, wherein the first and second electrodes comprise interdigitated electrodes disposed on an interior surface of the first glass substrate or on an interior surface of the second glass substrate. 19. The liquid crystal window of any of claims 15-18, further comprising a third glass substrate and a first interlayer disposed between the first glass substrate and the third glass substrate, a fourth glass substrate and a second interlayer disposed between the second glass substrate and the fourth glass substrate, or both. 20. The liquid crystal window of any of claims 15-19, wherein the cell gap d of the twisted nematic liquid crystal layer ranges from about 3 μm to about 10 μm. 21. The liquid crystal window of any of claims 15-20, wherein one or both of the first and second polarizers are independently chosen from iodine-based polarizers and dye-based polarizers. 22. The liquid crystal window of any of claims 15-21, wherein (a) the first transmission axis is parallel to a horizontal direction of the first and second glass substrates and the second transmission axis is orthogonal to the horizontal direction of the first and second glass substrates or (b) the first transmission axis is parallel to a vertical direction of the first and second glass substrates and the second transmission axis is orthogonal to the vertical direction of the first and second glass substrates. 23. The liquid crystal window of any of claims 15-22, wherein a transmittance of normally incident visible light having a wavelength ^ of 400 nm to 700 nm in the dark state is less than 0.5%. Attorney Docket No. SP22-232PCT 24. The liquid crystal window of any of claims 15-23, wherein a transmittance of incident light having a wavelength ^ of 550 nm and an incident angle of up to 80o is less than 3% in the dark state. 25. A method for switching the liquid crystal window of any of claims 15-24 from a transparent state to a dark state, the method comprising applying voltage to the first and second electrodes, the voltage ranging from about 3 to about 10 volts. 26. The method of claim 25, wherein a response time of the liquid crystal window for switching from the transparent state to the dark state ranges from about 20 milliseconds to about 200 milliseconds. 27. A liquid crystal window comprising: (a) a first polarizer having a first transmission axis, (b) a first glass substrate, (c) a first electrode, (d) a first alignment layer having a first alignment direction, (e) a first twisted nematic liquid crystal layer having a first extraordinary refractive index ne1, a first ordinary refractive index no1, a first cell gap d1, a first rotation direction R1, a first birefringence distribution B1, and a first retardation Re1 = (ne1-no1)*d1 for a wavelength ^ ranging from 400 nm to 700 nm; (f) a second alignment layer having a second alignment direction; (g) a second electrode; (h) an interstitial glass substrate; (i) a third alignment layer having a third alignment direction; (j) a second twisted nematic liquid crystal layer having a second extraordinary refractive index ne2, a second ordinary refractive index no2, a second cell gap d2, a second rotation direction R2; a second liquid crystal orientation distribution B2, and a second retardation Re2 = (ne2-no2)*d2 for a wavelength ^ ranging from 400 nm to 700 nm; (k) a fourth alignment layer having a fourth alignment direction; (l) a second glass substrate; (m) a second polarizer having a second transmission axis; Attorney Docket No. SP22-232PCT wherein: the first twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a dark state in the absence of applied voltage, and the liquid crystal window is in a transparent state when voltage is applied across the first and second electrodes; the first twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; the second twisted nematic liquid crystal layer is disposed between the third and fourth alignment layers and the third alignment direction is orthogonal to the fourth alignment direction; the first rotation direction R1 is opposite to the second rotation direction R2; the first retardation Re1 is substantially equal to the second retardation Re2; and the first and second transmission axes are orthogonal to each other. 28. The liquid crystal window of claim 27, wherein a first orientation of the first liquid crystal adjacent to the second alignment layer and a second orientation of the second liquid crystal adjacent to the third alignment layer are orthogonal to each other, parallel to each other, or at an angle between 0 and 90 degrees relative to each other, in the absence of applied voltage. 29. A liquid crystal window comprising: (a) a first polarizer having a first transmission axis, (b) a first glass substrate, (c) a first electrode, (d) a first alignment layer having a first alignment direction, (e) a first twisted nematic liquid crystal layer having a first extraordinary refractive index ne1, a first ordinary refractive index no1, a first cell gap d1, a first rotation direction R1, a first liquid crystal orientation distribution B1, and a first retardation Re1 = (ne1-no1)*d1 for a wavelength ^ ranging from 400 nm to 700 nm; (f) a second alignment layer having a second alignment direction; (g) a second electrode; (h) an interstitial glass substrate; Attorney Docket No. SP22-232PCT (i) a third alignment layer having a third alignment direction; (j) a second twisted nematic liquid crystal layer having a second extraordinary refractive index ne2, a second ordinary refractive index no2, a second cell gap d2, a second rotation direction R2; a second liquid crystal orientation distribution B2, and a second retardation Re2 = (ne2-no2)*d2 for a wavelength ^ ranging from 400 nm to 700 nm; (k) a fourth alignment layer having a fourth alignment direction; (l) a second glass substrate; (m) a second polarizer having a second transmission axis; wherein: the first twisted nematic liquid crystal layer is in electrical contact with the first and second electrodes, the liquid crystal window is in a transparent state in the absence of applied voltage, and the liquid crystal window is in a dark state when voltage is applied across the first and second electrodes; the first twisted nematic liquid crystal layer is disposed between the first and second alignment layers and the first alignment direction is orthogonal to the second alignment direction; the second twisted nematic liquid crystal layer is disposed between the third and fourth alignment layers and the third alignment direction is orthogonal to the fourth alignment direction; the first rotation direction R1 is opposite to the second rotation direction R2; the first retardation Re1 is substantially equal to the second retardation Re2; and the first and second transmission axes are parallel to each other. 30. The liquid crystal window of claim 29, wherein a first orientation of the first liquid crystal adjacent to the second alignment layer and a second orientation of the second liquid crystal adjacent to the third alignment layer are orthogonal to each other, parallel to each other, or at an angle between 0 and 90 degrees relative to each other, in the absence of applied voltage. 31. The liquid crystal window of claim 29 or 30, wherein the first and second electrodes comprise interdigitated electrodes disposed on an interior surface of the first glass substrate or on an interior surface of the second glass substrate. Attorney Docket No. SP22-232PCT 32. The liquid crystal window of any of claims 29-31, wherein the cell gap d1 of the first twisted nematic liquid crystal layer ranges from about 3 μm to about 30 μm, or the cell gap d2 of the second twisted nematic layer ranges from about 3 μm to about 30 μm, or both. 33. The liquid crystal window of any of claims 29-32, wherein one or both of the first and second polarizers are independently chosen from iodine-based polarizers and dye-based polarizers. 34. The liquid crystal window of any of claims 29-33, wherein a transmittance of normally incident visible light having a wavelength ^ of 400 nm to 700 nm in the dark state is less than 0.5%. 35. The liquid crystal window of any of claims 29-34, wherein a transmittance of normally incident visible light having a wavelength ^ of 400 nm to 700 nm is greater than 30% in the transparent state. 36. The liquid crystal window of any of claims 29-35, wherein a transmittance of incident light having a wavelength ^ of 550 nm and an incident angle of up to 80o is less than 1% in the dark state. 37. The liquid crystal window of any of claims 29-36, wherein a transmittance of incident light having a wavelength ^ of 550 nm and an incident angle of up to 80o is greater than 30% in the transparent state. 38. A liquid crystal window comprising: (a) a first polarizer having a first absorption axis; (b) a first compensation layer having a first optical axis varying in a first optical plane; (c) a first glass substrate; (d) a first electrode; (e) a first alignment layer having a first alignment direction; Attorney Docket No. SP22-232PCT (f) a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d; (g) a second alignment layer having a second alignment direction; (h) a second electrode; (i) a second glass substrate; (j) a second compensation layer having a second optical axis varying in a second optical plane; and (k) a second polarizer having a second absorption axis; wherein: the liquid crystal window comprises vertical and horizontal directions in a viewing plane of the liquid crystal window and a normal viewing direction perpendicular to the viewing plane; the first absorption axis, a first normal direction of the first optical plane, and the first alignment direction are aligned along a first vector; the second absorption axis, a second normal direction of the second optical plane, and the second alignment direction are aligned along a second vector that is orthogonal to the first vector; the first electrode continuously covers at least about 80% of the first glass substrate and the second electrode continuously covers at least about 80% of the second glass substrate; the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and is in electrical contact with the first and second electrodes; and the liquid crystal window is in a transparent state in the absence of applied voltage across the first and second electrodes. 39. The liquid crystal window of claim 38, wherein the first vector is 45o or 315o relative to the horizontal direction of the liquid crystal window and the second vector is 135o or 225o relative to the horizontal direction of the liquid crystal window. 40. The liquid crystal window of claim 38, wherein the first vector is 0o or 270o relative to the horizontal direction of the liquid crystal window and the second vector is 90o or 0o relative to the horizontal direction of the liquid crystal window. Attorney Docket No. SP22-232PCT 41. The liquid crystal window of any of claims 38-40, wherein the first and second electrodes form a single pixel across the entire liquid crystal window. 42. The liquid crystal window of any of claims 38-41, wherein one or both of the first and second polarizers are dye-based polarizers. 43. The liquid crystal window of any of claims 38-42, wherein the window has a contrast ratio of greater than 5 for a viewing angle of up to 80o relative to the normal viewing direction of the liquid crystal window when voltage is applied across the first and second electrodes. 44. The liquid crystal window of any of claims 38-43, wherein the cell gap of the twisted nematic liquid crystal layer is greater than 5 μm. 45. A method for switching the liquid crystal window of any of claims 38-44 from the transparent state, the method comprising applying a first voltage V1, a second voltage, V2, a third voltage V3, or a fourth voltage V4 across the first and second electrodes to switch the liquid crystal window into a first, second, third, or fourth state, respectively. 46. The method of claim 45, wherein the liquid crystal is switched between the first state and second state by applying first voltage V1 and second voltage V2, respectively, and wherein a first light transmittance along an upper viewing direction is lower than a second light transmittance along a lower viewing direction in the first state, and the first light transmittance is higher than the second light transmittance in the second state. 47. The method of claim 46, wherein the upper viewing direction is +80o relative to the normal direction of the liquid crystal window and the lower viewing direction is -80o relative to the normal viewing direction of the liquid crystal window. 48. The method of claim 45, wherein the liquid crystal is switched between the third state and fourth state by applying third voltage V3 and fourth voltage V4, respectively, and wherein a third light transmittance along an upper-right viewing Attorney Docket No. SP22-232PCT direction is lower than a fourth light transmittance along a lower-left viewing direction in the third state, and the third light transmittance is higher than the fourth light transmittance in the fourth state. 49. The method of claim 48, wherein the upper-right viewing direction is +80o relative to the normal direction of the liquid crystal window and the lower-left viewing direction is -80o relative to the normal viewing direction of the liquid crystal window. 50. A liquid crystal window comprising: (a) a first polarizer having a first absorption axis; (b) a first compensation layer having a first optical axis varying in a first optical plane; (c) a first glass substrate; (d) a first electrode; (e) a first alignment layer having a first alignment direction; (f) a twisted nematic liquid crystal layer having an extraordinary refractive index ne, an ordinary refractive index no, and a cell gap d greater than 5μm; (g) a second alignment layer having a second alignment direction; (h) a second electrode; (i) a second glass substrate; (j) a second compensation layer having a second optical axis varying in a second optical plane; and (k) a second polarizer having a second absorption axis; wherein: the first absorption axis, a first normal direction of the first optical plane, and the first alignment direction are aligned along a first vector; the second absorption axis, a second normal direction of the second optical plane, and the second alignment direction are aligned along a second vector that is orthogonal to the first vector; the twisted nematic liquid crystal layer is disposed between the first and second alignment layers and is in electrical contact with the first and second electrodes; and the liquid crystal window is in a transparent state in the absence of applied voltage across the first and second electrodes. Attorney Docket No. SP22-232PCT 51. A method for switching the liquid crystal window of claim 50 from the transparent state to a dark state, the method comprising applying voltage across the first and second electrodes. 52. The method of claim 51, wherein the voltage ranges from about 3 volts to about 8 volts. 53. The method of claim 51, wherein the first and second electrodes are configured to drive no more than 25 pixels. 54. The method of clam 51, wherein the first and second electrodes are configured to drive a single pixel.
PCT/US2023/037229 2022-11-14 2023-11-14 Liquid crystal windows comprising at least one twisted nematic liquid crystal layer and at least one polarizer WO2024107415A1 (en)

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Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4483700A (en) 1983-08-15 1984-11-20 Corning Glass Works Chemical strengthening method
US5674790A (en) 1995-12-15 1997-10-07 Corning Incorporated Strengthening glass by ion exchange
US20040036821A1 (en) * 2002-08-22 2004-02-26 Optiva, Inc. Liquid crystal shutter
EP0835475B1 (en) * 1995-06-26 2004-09-01 Minnesota Mining And Manufacturing Company Optical panel capable of switching between reflective and transmissive states
US7666511B2 (en) 2007-05-18 2010-02-23 Corning Incorporated Down-drawable, chemically strengthened glass for cover plate
US20110242462A1 (en) * 2006-02-28 2011-10-06 Fujifilm Corporation Polarizing plate and liquid crystal display
US20170115527A1 (en) * 2014-06-13 2017-04-27 Sharp Kabushiki Kaisha Liquid crystal display device
US20220349246A1 (en) * 2019-07-02 2022-11-03 Merck Patent Gmbh Switchable optical device and switchable glazing unit

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4483700A (en) 1983-08-15 1984-11-20 Corning Glass Works Chemical strengthening method
EP0835475B1 (en) * 1995-06-26 2004-09-01 Minnesota Mining And Manufacturing Company Optical panel capable of switching between reflective and transmissive states
US5674790A (en) 1995-12-15 1997-10-07 Corning Incorporated Strengthening glass by ion exchange
US20040036821A1 (en) * 2002-08-22 2004-02-26 Optiva, Inc. Liquid crystal shutter
US20110242462A1 (en) * 2006-02-28 2011-10-06 Fujifilm Corporation Polarizing plate and liquid crystal display
US7666511B2 (en) 2007-05-18 2010-02-23 Corning Incorporated Down-drawable, chemically strengthened glass for cover plate
US20170115527A1 (en) * 2014-06-13 2017-04-27 Sharp Kabushiki Kaisha Liquid crystal display device
US20220349246A1 (en) * 2019-07-02 2022-11-03 Merck Patent Gmbh Switchable optical device and switchable glazing unit

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
HIROYUKI MORI ET AL., JPN. J. APPL. PHYS., vol. 36, 1997, pages 143

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