CN117406498A - Composite photoalignment layer - Google Patents
Composite photoalignment layer Download PDFInfo
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- CN117406498A CN117406498A CN202311122049.XA CN202311122049A CN117406498A CN 117406498 A CN117406498 A CN 117406498A CN 202311122049 A CN202311122049 A CN 202311122049A CN 117406498 A CN117406498 A CN 117406498A
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- 239000002131 composite material Substances 0.000 title claims abstract description 84
- 239000000463 material Substances 0.000 claims abstract description 67
- 239000000987 azo dye Substances 0.000 claims abstract description 57
- 239000000178 monomer Substances 0.000 claims abstract description 56
- 239000004973 liquid crystal related substance Substances 0.000 claims abstract description 31
- 238000000034 method Methods 0.000 claims abstract description 23
- 239000003999 initiator Substances 0.000 claims abstract description 20
- 239000000758 substrate Substances 0.000 claims abstract description 16
- 239000007787 solid Substances 0.000 claims abstract description 14
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- LODHFNUFVRVKTH-ZHACJKMWSA-N 2-hydroxy-n'-[(e)-3-phenylprop-2-enoyl]benzohydrazide Chemical compound OC1=CC=CC=C1C(=O)NNC(=O)\C=C\C1=CC=CC=C1 LODHFNUFVRVKTH-ZHACJKMWSA-N 0.000 claims description 4
- YGSDEFSMJLZEOE-UHFFFAOYSA-N Salicylic acid Natural products OC(=O)C1=CC=CC=C1O YGSDEFSMJLZEOE-UHFFFAOYSA-N 0.000 claims description 4
- 239000002253 acid Substances 0.000 claims description 4
- 229960004889 salicylic acid Drugs 0.000 claims description 4
- QAOWNCQODCNURD-UHFFFAOYSA-L sulfate group Chemical group S(=O)(=O)([O-])[O-] QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 claims description 4
- 239000012956 1-hydroxycyclohexylphenyl-ketone Substances 0.000 claims description 2
- QSVOWVXHKOQYIP-UHFFFAOYSA-N 2-dodecylsulfanylcarbothioylsulfanyl-2-methylpropanenitrile Chemical group CCCCCCCCCCCCSC(=S)SC(C)(C)C#N QSVOWVXHKOQYIP-UHFFFAOYSA-N 0.000 claims description 2
- -1 3-acryloxypropoxy Chemical group 0.000 claims description 2
- MQDJYUACMFCOFT-UHFFFAOYSA-N bis[2-(1-hydroxycyclohexyl)phenyl]methanone Chemical group C=1C=CC=C(C(=O)C=2C(=CC=CC=2)C2(O)CCCCC2)C=1C1(O)CCCCC1 MQDJYUACMFCOFT-UHFFFAOYSA-N 0.000 claims description 2
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- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 description 9
- 239000000203 mixture Substances 0.000 description 8
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Classifications
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- 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
- G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
- G02F1/133711—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by organic films, e.g. polymeric films
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F120/00—Homopolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride, ester, amide, imide or nitrile thereof
- C08F120/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
- C08F120/52—Amides or imides
- C08F120/54—Amides, e.g. N,N-dimethylacrylamide or N-isopropylacrylamide
- C08F120/58—Amides, e.g. N,N-dimethylacrylamide or N-isopropylacrylamide containing oxygen in addition to the carbonamido oxygen, e.g. N-methylolacrylamide, N-acryloyl morpholine
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L101/00—Compositions of unspecified macromolecular compounds
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K19/00—Liquid crystal materials
- C09K19/52—Liquid crystal materials characterised by components which are not liquid crystals, e.g. additives with special physical aspect: solvents, solid particles
- C09K19/54—Additives having no specific mesophase characterised by their chemical composition
- C09K19/56—Aligning agents
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- 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
- G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
- G02F1/13378—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by treatment of the surface, e.g. embossing, rubbing or light irradiation
- G02F1/133788—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by treatment of the surface, e.g. embossing, rubbing or light irradiation by light irradiation, e.g. linearly polarised light photo-polymerisation
-
- 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
- G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
- G02F1/133711—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by organic films, e.g. polymeric films
- G02F1/133715—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by organic films, e.g. polymeric films by first depositing a monomer
-
- 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
- G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
- G02F1/133711—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by organic films, e.g. polymeric films
- G02F1/133726—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers by organic films, e.g. polymeric films made of a mesogenic material
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- Physics & Mathematics (AREA)
- Chemical & Material Sciences (AREA)
- Nonlinear Science (AREA)
- Crystallography & Structural Chemistry (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Mathematical Physics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Health & Medical Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Medicinal Chemistry (AREA)
- Polymers & Plastics (AREA)
- Liquid Crystal (AREA)
Abstract
A composite photoalignment layer for aligning liquid crystal molecules, comprising: a monomer material, a photoinitiator or a thermal initiator, and an azo dye material. A method of preparing a composite photoalignment layer for aligning liquid crystal molecules, comprising: mixing the monomer material, the photoinitiator or thermal initiator, and the azo dye material in solution; coating the mixed solution on a substrate to form a film; exposing the film to polarized light; and heating the film to polymerize the monomer material and form a solid film with the thermal initiator.
Description
Cross-reference to related applications
This patent application claims priority from U.S. provisional patent application Ser. No.62/285,435, filed on 29 th 10 months 2015, and U.S. provisional patent application Ser. No.62/493,840, filed on 7 months 2016, the entire contents of both applications being incorporated herein by reference.
Background
Recently, flat panel conversion displays, fringe field switching displays, and ferroelectric liquid crystal based field sequential color displays have become popular because they provide relatively high optical performance and resolution, and idealized display cells have fast response times, wide viewing angles, and high resolution. For example, the use of an electrically suppressed helix ferroelectric liquid crystal provides excellent optical properties (like nematic liquid crystals) while also having a relatively fast switching response and a relatively low driving voltage.
Liquid crystal display cells with fast response, high resolution and high optical contrast are for example applicable to fast response optics such as modulators, filters, attenuators, and to displays with high resolution requirements such as micro projectors, 3D displays, micro displays, high Definition Televisions (HDTVs), ultra High Definition (UHDs) displays etc.
Summary of The Invention
In one exemplary embodiment, the present invention provides a composite photoalignment layer for aligning liquid crystal molecules, comprising: a monomer material, a photoinitiator, and an azo dye material.
In another exemplary embodiment, the present invention provides a method of preparing a composite photoalignment layer for aligning liquid crystal molecules, the method comprising: mixing the monomer material, photoinitiator and azo dye material in solution; coating the mixed solution on a substrate to form a film; the film is exposed to polarized light to form a solid film.
In another exemplary embodiment, the present invention provides a composite photoalignment layer for aligning liquid crystal molecules, comprising: monomer materials, thermal initiators, and azo dye materials.
In another exemplary embodiment, the present invention provides a method of preparing a composite photoalignment layer for aligning liquid crystal molecules, the method comprising: mixing the monomer material, the thermal initiator and the azo dye material in solution; coating the mixed solution on a substrate to form a film; exposing the film to polarized light to effect single domain or multi-domain alignment; the film is heated to polymerize the monomer material and form a solid film.
Brief description of the drawings
Fig. 1 is an illustration of an exemplary method of preparing a composite photoalignment layer for aligning liquid crystal molecules according to a first exemplary embodiment.
Fig. 2A-2B show transmittance versus voltage curves (TVCs) of an exemplary Twisted Nematic (TN) display cell before and after heat exposure.
Fig. 3A-3B illustrate TVCs of an exemplary Electrically Controlled Birefringence (ECB) nematic display cell before and after thermal exposure.
Fig. 4A-4B illustrate TVCs of exemplary TN display cells before and after light exposure.
Fig. 5A-5B illustrate TVCs of exemplary ECB nematic display cells before and after light exposure.
Fig. 6 depicts an optical structure illustration of a multi-domain alignment.
Fig. 7 is an illustration of an exemplary method of preparing a composite photoalignment layer for aligning liquid crystal molecules according to a second exemplary embodiment.
Fig. 8 illustrates TVC of an exemplary TN display cell before and after heat exposure.
Fig. 9 illustrates TVCs of exemplary ECB nematic display cells before and after thermal exposure.
Fig. 10 illustrates TVCs of exemplary TN display cells before and after light exposure.
Fig. 11 illustrates TVCs of an exemplary ECB nematic display cell before and after light exposure.
Fig. 12 is a graph showing the time dependence of Residual Direct Current (RDC) voltage after a display cell made of the composite photoalignment layer is applied with 10V for 1 hour.
FIG. 13 depicts an exemplary optical structure representation of multi-domain alignment.
Detailed Description
For electro-optic mode and pixel structure modulation required for certain liquid crystal display cells with fast responsiveness, high resolution, and high optical contrast, highly optimized photoalignment may be required to provide zero degree pretilt angle, large surface uniformity, and multi-domain alignment (multi-domain alignment in a pixel improves visual presentation and viewing characteristics).
Conventional photoalignment materials do not provide all of the above characteristics. The conventional azo dye alignment layer can provide good alignment (high anchoring energy, small pretilt angle and relatively large area uniformity) for the liquid crystal display unit, so that the liquid crystal display unit can obtain very high pixel resolution. However, conventional azo dye alignment layers are unstable to chemical, thermal and light exposure.
In an exemplary embodiment of the present invention, a composite photoalignment layer for liquid crystals is provided, which comprises a composite formed by mixing at least one monomer ("monomer material"), a thermal radical initiator ("thermal initiator") or a photoinitiator, and an azo dye material (e.g., SD1 azo dye). By incorporating a polymer network into the azo material (via thermally or photo-initiated polymerization), exemplary embodiments of the present invention provide a stable complex azo dye photoalignment layer that is stable against ultraviolet light, heat, and other environmental conditions.
The composite photoalignment layer provides good alignment properties (e.g., low pretilt angle, high polarity and azimuthal anchoring energy, low Residual Direct Current (RDC) voltage, high Voltage Holding Ratio (VHR), low image retention parameters) that are comparable to conventional polyimide films and meet industry and consumer requirements (e.g., RDC voltage, VHR, and anchoring energy). Thus, the composite photoalignment layer is suitable for use in various optoelectronic devices and displays, including but not limited to in-plane switching displays (IPS) and Ferroelectric Liquid Crystal (FLC) displays.
In a first exemplary embodiment, starting with a mixture of monomers, photoinitiator and azo dye material (which provides stability to the azo dye material at the formulation concentration but does not affect the alignment provided by the photoalignment layer), a single exposure simultaneously achieves photoinitiated redirection (photoalignment) of the azo dye material and polymerization of the monomers, resulting in a composite photoalignment layer with good alignment characteristics (such as high anchoring energy, small pretilt angle and relatively large area uniformity). The composite photoalignment layer is thus formed in a single irradiation/exposure step, providing good and stable photoalignment of the liquid crystal.
In a second exemplary embodiment, the process begins with mixing the monomer, the thermal initiator, and the azo dye material (at a configured concentration that provides stability to the azo dye material but does not affect the alignment provided by the photoalignment layer). Then, in a first step, a preferred alignment of the easy axis of magnetization of the azo dye photoalignment layer is achieved. In the second step, thermal polymerization is carried out.
In one-step irradiation/exposure, photoalignment enables single-domain or multi-domain alignment with very small pretilt angles. With a single photo-alignment method, such as a patterned wave plate, a multi-domain photo-alignment layer with a highly uniform alignment over a large size range can be obtained. Furthermore, since azo dye materials only provide planar molecular dispersion from one direction to the other, and do not go out of plane, the pretilt angle produced is very small.
Further, according to an exemplary embodiment of the present invention, the anchoring energy of the composite photoalignment layer may be adjusted by controlling the exposure amount. Thus, exemplary embodiments of the present invention are suitable for applications requiring precise control of anchoring energy, including, but not limited to, ferroelectric liquid crystal displays, for example.
After irradiation with polarized light having a sufficiently high irradiation energy of a specific wavelength (polarized light exerts an alignment direction on the photoalignment layer), the liquid crystal photoalignment layer will show a preferred alignment direction. Photoalignment offers several advantages over conventional rubbing alignment techniques. For example, friction may cause mechanical damage or static electricity, which reduces manufacturing yield. Photoalignment avoids mechanical contact with the alignment layer, thereby minimizing mechanical damage and static electricity (particularly advantageous for FLC devices). For large substrates, photoalignment is easier to implement and can provide better uniformity for high resolution displays. Furthermore, photoalignment enables multi-domain alignment on the micrometer scale, even on the nanometer scale. Furthermore, photoalignment may be applied to non-planar surfaces, such as curved surfaces or surfaces with microscopic limitations.
Photoalignment has several pathways, including, for example, the following: (1) photoalignment of azo molecules by cis-trans isomerisation; (2) photocrosslinking the monomers into a polymer; (3) photodegradation of the polymer film; and (4) light-induced redirection of azo dye molecules. Among other things, light-induced redirection of azo dye molecules provides certain advantages, such as sufficiently high polarity and azimuthal anchoring energy for liquid crystal alignment, which is as strong as commercial polyimide films based on conventional rubbing; high Voltage Holding Ratio (VHR) and low Residual Direct Current (RDC) voltage are low, which is advantageous for liquid crystal alignment; and very small pretilt angles (e.g., less than 1 degree), which is advantageous for display modes requiring such low pretilt angles, such as in-plane switching (IPS) mode and its derivatives, such as Fringe Field Switching (FFS) mode. Furthermore, polarized light of a wide range of wavelengths may enable light-induced redirection of azo dyes, including for example 450nm blue light. This allows the use of high power Light Emitting Diodes (LEDs) as light sources in order to reduce the equipment costs for photoalignment.
Thus, photoalignment of azo dye molecules based on light-induced redirection enables sufficiently high polar and azimuthal anchoring energy, high VHR, proper pretilt angle and uniform alignment. In addition, photoalignment of azo dye molecules based on photoinduced redirection can be easily rotated using blue light and provide anchoring energy comparable to commercial polyimide films with very low pretilt angles. Photoalignment of azo dye molecules based on photoinduced redirection can be used in a wide range of LC devices, including for example IPS and FLC displays. The photoalignment of azo dye molecules based on photoinduced redirection is adjustable based on controlling the irradiation energy dose. Photoalignment of azo dye molecules based on photoinduced redirection can further provide multi-domain alignment with well-defined easy axis alignment. In addition, photoalignment of azo dye molecules based on photoinduced redirection can provide alignment in the nanometer domain, which can provide better viewing angle, optics and other characteristics for liquid crystal displays.
However, as described above, photodegradation and instability of conventional azo dye photoalignment layers have prevented development of azo dye photoalignment layers in certain real world applications. In particular, if the photoaligned display unit is exposed to light, the easy axis of magnetization of the photoalignment layer of azo dye may change and damage alignment quality of the display unit. Furthermore, the light flux from the backlight of the display system is strong enough to deteriorate the alignment characteristics of the photoalignment layer within several hours of operation.
In a first exemplary embodiment, the present invention provides a composite photoalignment layer for liquid crystals comprising monomers, photoinitiators and azo dye materials in optimal relative concentration ratios. The composite photoalignment layer provides good, uniform alignment and is stable after irradiation with a light source. The concentrations of photoinitiator and monomer were adjusted to achieve both alignment and stabilization in a single irradiation.
In one exemplary embodiment, the monomer has liquid crystalline properties and is a liquid crystal reactive moiety; the azo dye is the acid sulfate dye tetrasodium 5,5' - ((1 e,1' e) - (2, 2' -disulfonic acid- [1,1' -biphenyl ] -4,4' -diyl) bis (diazene-2, 1-diyl)) bis (2-hydroxybenzoic acid) ("SD 1"); the photoinitiator is 1-hydroxycyclohexyl phenyl ketone. It should be appreciated that in other exemplary embodiments, other materials may be used.
In one example, the process of preparing the composite photoalignment layer begins with mixing the monomer and azo dye at an optimal relative concentration of 50:50 (because the molecular lengths of the azo dye and monomer are approximately the same). Then, a photoinitiator was added to the mixture at 10% wt/wt of the monomers. It should be understood that other relative concentrations of materials may be used in other exemplary embodiments and when other materials are used.
The concentration of the photoinitiator is adjusted to optimize the polymerization rate (e.g., to ensure that polymerization is not completed before photoalignment, which would otherwise affect optical quality). In various exemplary embodiments, the concentration of photoinitiator added to the mixture relative to the monomer material may be varied between 1% wt/wt and 10% wt/wt to optimize the balance between alignment rate (to achieve a specific amount of liquid crystal anchoring energy) and polymerization rate. Further, based on the relationship between the absorption band of the photoinitiator and the absorption band of the azo dye, a different balance between the alignment rate and the polymerization rate can be obtained. In one example, the appropriate photoinitiator absorption band is selected to match the absorption band of the azo dye (e.g., SD1 azo dye has absorption peaks at 365nm and 450 nm). In other examples, the absorption band of the photoinitiator is different from the absorption band of the azo dye.
In addition, the azimuthal anchoring energy of the composite photoalignment layer can be tuned by varying the irradiation energy and by balancing the alignment rate and the polymerization rate.
A method of preparing a composite photoalignment layer for aligning liquid crystal molecules, comprising: mixing the monomer material, the photoinitiator and the azo dye material in solution; coating the mixed solution on a substrate to form a film; the film is exposed to polarized light to form a solid film. The film is exposed in one step while providing alignment and polymerization to the composite photoalignment layer. The composite photoalignment layer may be coated on the substrate surface based on a variety of coating techniques including, but not limited to, spin coating, doctor blade, and screen printing, for example. Polarized light may come from a polarized light source having one or more primary wavelength components (e.g., such that different illumination bands may be used for alignment and polymerization).
Fig. 1 depicts a legend for the method. As shown in fig. 1, at stage 101, a mixture of SD1 azo dye, monomer and photoinitiator in solution mixed in a solvent such as Dimethylformamide (DMF) is coated on a substrate to form a film at stage 102. Then, in stage 103, the film is exposed in one step to simultaneously provide a ligand for the composite photoalignment layerAnd (3) to and polymerize to form a solid film in stage 104, wherein the solid film contains a polymer network formed by SD1 molecules and monomers. In particular, polymerization of the monomer material in the composite photoalignment layer enables the composite photoalignment layer to form a solid film, and the polymerization of the monomer material provides a high liquid crystal anchoring energy (e.g., -10 -3 J/m 2 ). It should be understood that the monomer material may be completely polymerized according to exemplary embodiments of the present invention.
The specific level of anchoring energy may be adjusted based on the dose of radiation. In one example, 10 can be obtained -4 J/m 2 To 10 -2 J/m 2 Anchoring energy within a range (e.g., about 10 -4 J/m 2 Or 10 -3 J/m 2 On the order of magnitude of (c). Further, it should be appreciated that the anchoring energy may be adjusted to a dose of 10 -4 J/m 2 To 10 -2 J/m 2 Is adjusted within the range of (2).
In an exemplary embodiment, the composite photoalignment layer exhibits a low RDC voltage, for example, less than 10mV.
In one exemplary embodiment, the composite photoalignment layer provides the same or similar electro-optic characteristics as conventional polyimide alignment layers. In one example, the voltage holding ratio of a planar aligned nematic liquid crystal cell with the composite photoalignment layer is higher than 99% for a 60Hz frame rate.
In one exemplary embodiment, the composite photoalignment layer has alignment quality comparable to conventional and commercially available alignment layers.
In one exemplary embodiment, the fully polymerized monomer composite photoalignment layer provides an image retention parameter ("ISP") ratio of 1.01, which is comparable to conventional alignment layers. The image retention parameter defines the behavior of the display panel competing with the residual image of the previous frame. In one example, the 6V voltage is applied for 6 hours to one of the two pixels in one cell, the other pixel is held at 0V, and the transmittance of the two pixels at 2V voltage is compared, and based on this application, the ISP ratio is proved to be 1.01.
In one exemplary embodiment, the composite photoalignment layer proved to be thermally stable, as it showed no signs of degradation after 24 hours of heat exposure in an oven at 100 ℃. As shown in fig. 2A-2B and fig. 3A-3B, the transmittance versus voltage curve (TVC) of an exemplary display cell having the composite photoalignment layer is unaffected after thermal exposure. Fig. 2A-2B illustrate TVCs of exemplary Twisted Nematic (TN) display cells before and after thermal exposure. Fig. 3A-3B illustrate TVCs of an exemplary Electrically Controlled Birefringence (ECB) nematic display cell before and after thermal exposure. The alignment quality of the exemplary display unit is also unaffected by the thermal exposure, as is evident from visual inspection.
It was also confirmed that the composite photoalignment layer was optically stable and exposed to an intensity of 100mW/cm 2 Without any degradation after 1 hour of the light source of (c). As shown in fig. 4A-4B and fig. 5A-5B, the TVC of the exemplary display cell having the composite photoalignment layer is unaffected after exposure. Fig. 4A-4B illustrate TVCs of an exemplary TN display cell before and after exposure. Fig. 5A-5B illustrate TVCs of an exemplary ECB nematic display cell before and after exposure. The alignment quality of the exemplary display unit is also unaffected by the exposure, as is evident from visual inspection.
In one exemplary embodiment, during one exposure of stage 103 of fig. 1, a phase mask is used to provide two or more alignment domains for the composite photoalignment layer. In one example, a dual domain patterned half wave plate with a feature size of 20 μm is used as a phase mask. The phase mask rotates the plane of incident light, after which the substrate coated with the composite photoalignment layer is irradiated with incident light of a degraded polarization plane. As a result, the irradiated substrate provides stable and heat and light resistant multi-domain alignment, which has both high quality optical and electrical parameters. An illustration of the optical texture of multi-domain alignment is depicted in fig. 6.
In a second exemplary embodiment, the present invention provides a composite photoalignment layer for liquid crystals comprising monomers, thermal initiators and azo dye materials at optimal relative concentrations. The composite photoalignment layer provides good, uniform alignment after being irradiated by a light source and is stable after heating (e.g. heating at 230 ℃ for 30 minutes, although it will be appreciated that other times and temperatures may be used). The concentrations of thermal initiator and monomer are adjusted to provide good alignment and alignment stability at the same time.
In one exemplary embodiment, the monomer has liquid crystalline properties, which is 4- (3-acryloxypropoxy) -benzoic acid-2-methyl-1, 4-phenyl ester; the azo dye material is the acid sulfate dye tetrasodium 5,5' - ((1 e,1' e) - (2, 2' -disulfonic acid- [1,1' -biphenyl ] -4,4' -diyl) bis (diazene-2, 1-diyl)) bis (2-hydroxybenzoic acid) ("SD 1"); the thermal initiator is 2-cyano-2-propyl dodecyl trithiocarbonate. It should be appreciated that in other exemplary embodiments, other materials may be used.
In one example, the process of preparing the composite photoalignment layer begins with mixing the monomer and azo dye at an optimal relative concentration of 50:50 (because the molecular lengths of the azo dye and monomer are approximately the same). Then, a thermal initiator accounting for 5% wt/wt of the monomer was added to the mixture. The mixture is further dissolved in a solvent (e.g., dimethylformamide or other polar solvent). It should be appreciated that other relative concentrations of materials may be used in other exemplary embodiments or for other materials.
In one exemplary embodiment, the azo dye and the combined monomer concentration is 1% wt/wt of the solvent and the thermal initiator concentration is 5% wt/wt of the monomer. It should be appreciated that other relative concentrations of materials may be used in other exemplary embodiments or for other materials.
A method of preparing a composite photoalignment layer for aligning liquid crystal molecules, comprising: mixing the monomer material, the thermal initiator and the azo dye material in solution; coating the mixed solution on a substrate to form a thin film; exposing the film to polarized light to perform single domain or multi domain alignment; the film is heated to form a solid film. The exposing and heating of the film may be performed simultaneously as part of one step or in a separate sequence of steps. The alignment characteristics (such as anchoring energy and surface uniformity) of the composite photoalignment layer are not affected by thermal polymerization initiated by heating the film.
FIG. 7 depicts a legend for the method. As shown in fig. 7, at stage 701, a mixture of SD1 azo dye, monomer and thermal initiator in solution is spin coated onto a substrate to form a film at stage 702. Then, in stage 703, the film is exposed in one step to provide alignment to the composite photoalignment layer, and in stage 704, the film is heated at 230 ℃ for 30 minutes to form a solid film having a polymer network formed of SD1 molecules and monomers in stage 705. In particular, polymerization of the monomer material in the composite photoalignment layer forms the composite photoalignment layer into a solid film, the polymerization of the monomer material providing a high liquid crystal anchoring energy (e.g., -10 - 3 J/m 2 ). It should be understood that the monomer material may be fully polymerized according to exemplary embodiments of the present invention.
The specific level of anchoring energy may be adjusted based on the dose of radiation. For example, 10 can be obtained -4 J/m 2 To 10 -2 J/m 2 Anchoring energy within a range (e.g., about 10 -4 J/m 2 Or 10 -3 J/m 2 On the order of magnitude of (c). In another example, about 3x10 may be obtained -3 J/m 2 Is used for anchoring. Further, it should be appreciated that the anchoring energy may be adjusted to 10 by adjusting the dose of the radiation -4 J/m 2 To 10 -2 J/m 2 Is adjusted within the range of (2).
In one exemplary embodiment, the composite photoalignment layer provides the same or similar electro-optic characteristics as conventional polyimide alignment layers. In one example, the voltage holding ratio of a planar aligned nematic liquid crystal cell with the composite photoalignment layer is higher than 99% for a 60Hz frame rate.
In one exemplary embodiment, the composite photoalignment layer has alignment quality comparable to conventional and commercially available alignment layers.
In one exemplary embodiment, the composite photoalignment layer proved to be thermally stable, as it did not show any signs of deterioration after 24 hours of heat exposure in an oven at 100 ℃. As shown in fig. 8 and 9, the TVC of the exemplary display unit having the composite photoalignment layer is not affected after the thermal exposure. Fig. 8 shows TVC of an exemplary TN display cell before and after heat exposure. Fig. 9 shows TVC of an exemplary ECB nematic display cell before and after thermal exposure. The alignment quality of the exemplary display unit is also unaffected by the thermal exposure, as is evident from visual inspection.
It was also confirmed that the composite photoalignment layer was optically stable and was subjected to 400J/cm at a wavelength of 450nm 2 The energy source does not show any degradation after exposure. As shown in fig. 10 and 11, the TVC of the exemplary display unit having the composite photoalignment layer is not affected after exposure. Fig. 10 illustrates TVC of an exemplary TN display cell before and after exposure. Fig. 11 illustrates TVC of an exemplary ECB nematic display cell before and after exposure. The alignment quality of the exemplary display unit is also unaffected by the exposure, as is evident from visual inspection.
In an exemplary embodiment, the composite photoalignment layer exhibits a low RDC voltage, e.g., less than 10mV, after 1 hour loading with a 10V dc voltage, e.g., at 60 °. FIG. 12 shows RDC over time after an exemplary composite photoalignment layer was pressurized at 10V for 1 hour.
In one exemplary embodiment, during one exposure of stage 703 of fig. 7, a phase mask is used to provide the composite photoalignment layer with two or more alignment domains having different alignment directions in adjacent regions. As a result, the irradiated substrate provides stable and heat and light resistant multi-domain alignment, which has both high quality optical and electrical parameters. An illustration of the optical texture with multi-domain alignment of a checkerboard pattern with a feature size of 20 μm is shown in fig. 13.
Thus, exemplary embodiments of the present invention provide a composite photoalignment layer with monomers fully polymerized while providing acceptable residual DC voltage, image retention parameters, and voltage retention values. In one example, the monomer fully polymerized composite photoalignment layer provides a minimum and acceptable residual DC voltage value of 0.008V, a minimum and acceptable image-to-residual parameter ratio of 1.01, and a minimum and acceptable voltage holding ratio above 99% at 60 ℃ and 60Hz frame frequency.
All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein.
The use of the terms "a" and "an" and "the" and "at least one" and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term "at least one" followed by one or more items (e.g., "at least one of a and B") should be interpreted as a selection of one item from the list of items (a or B) or any combination of two or more of the list of items (a and B), unless otherwise indicated herein or clearly contradicted by context. The terms "comprising," "having," "including," and "containing" are to be construed as open-ended terms (i.e., meaning "including, but not limited to,") unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., "such as") provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.
Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.
Claims (20)
1. A composite photoalignment layer for aligning liquid crystal molecules, comprising:
a monomer material;
a photoinitiator; and
azo dye materials.
2. The composite photoalignment layer according to claim 1, wherein the composite photoalignment layer is exposed to a polarized light source to perform single domain or multi-domain alignment on the composite photoalignment layer, and a monomer material is polymerized to form a solid film.
3. The composite photoalignment layer of claim 1, wherein the composite photoalignment layer is coated on a surface of a substrate.
4. A composite photoalignment layer according to claim 3, wherein the composite photoalignment layer is coated on the substrate surface via spin coating, doctor blade or screen printing.
5. The composite photoalignment layer according to claim 1, wherein the photoinitiator is 1-hydroxycyclohexyl phenyl ketone.
6. The composite photoalignment layer according to claim 1, wherein the monomeric material is a liquid crystal reactive primitive.
7. The composite photoalignment layer according to claim 1, wherein the azo dye material is the acid sulfate group azo dye tetrasodium 5,5' - ((1 e,1' e) - (2, 2' -disulfonic acid- [1,1' -biphenyl ] -4,4' -diyl) bis (diazene-2, 1-diyl)) bis (2-hydroxybenzoic acid).
8. The composite photoalignment layer according to claim 1, wherein the photoinitiator has a concentration of about 1% wt/wt to about 10% wt/wt of the monomer material.
9. A method of preparing a composite photoalignment layer for aligning liquid crystal molecules, comprising:
mixing the monomer material, the photoinitiator and the azo dye material in solution;
coating the mixed solution on a substrate to form a film; and
the film is exposed to polarized light to form a solid film.
10. The method of claim 9, wherein exposing the thin film is a one-step exposure while providing alignment and polymerization to the composite photoalignment layer.
11. The method of claim 9, wherein the polarized light is from a polarized light source having one or more primary wavelength components.
12. A composite photoalignment layer for aligning liquid crystal molecules, comprising:
a monomer material;
a thermal initiator; and
azo dye materials.
13. The composite photoalignment layer according to claim 12, wherein the composite photoalignment layer is exposed to a polarized light source to perform single domain or multi-domain alignment on the composite photoalignment layer, and the monomer material is thermally polymerized to form a solid film.
14. The composite photoalignment layer according to claim 12, wherein the thermal initiator is 2-cyano-2-propyldodecyl trithiocarbonate.
15. The composite photoalignment layer according to claim 12, wherein the monomer material is 4- (3-acryloxypropoxy) -benzoic acid-2-methyl-1, 4-phenyl ester.
16. The composite photoalignment layer according to claim 12, wherein the azo dye material is the acid sulfate group azo dye tetrasodium 5,5' - ((1 e,1' e) - (2, 2' -disulfonic acid- [1,1' -biphenyl ] -4,4' -diyl) bis (diazene-2, 1-diyl)) bis (2-hydroxybenzoic acid).
17. The composite photoalignment layer according to claim 12, wherein the monomer material, thermal initiator and azo dye material are dissolved in a solvent.
18. The composite photoalignment layer according to claim 17, wherein the concentration of the azo dye material and the bound monomer material is 1% wt/wt of the solvent.
19. The composite photoalignment layer according to claim 12, wherein the concentration of the thermal initiator is about 5% wt/wt of the monomer material.
20. A method of preparing a composite photoalignment layer for aligning liquid crystal molecules, comprising:
mixing the monomer material, the thermal initiator and the azo dye material in solution; coating the mixed solution on a substrate to form a film;
exposing the film to a polarized light source to effect single domain or multi-domain alignment; and
the film is heated to polymerize the monomer material to form a solid film.
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| US62/493,840 | 2016-07-19 | ||
| CN201680033894.1A CN107710058A (en) | 2015-10-29 | 2016-10-28 | Compound photo-alignment layer |
| PCT/CN2016/103739 WO2017071637A1 (en) | 2015-10-29 | 2016-10-28 | Composite photoalignment layer |
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| CN201680033894.1A Division CN107710058A (en) | 2015-10-29 | 2016-10-28 | Compound photo-alignment layer |
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| CN110716352B (en) * | 2018-07-12 | 2022-11-15 | 香港科技大学 | Composition for preparing liquid crystal photoalignment layer and application method thereof |
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| EP2159611B1 (en) * | 2003-11-06 | 2018-01-03 | Sumitomo Chemical Company, Limited | Polymerizable liquid crystal and oriented polymer film |
| TWI406061B (en) * | 2005-11-10 | 2013-08-21 | Dainippon Ink & Chemicals | Composition for photoalignment film, optically anisotropic body and method of producing same |
| US9791743B2 (en) * | 2013-07-26 | 2017-10-17 | Nano And Advanced Materials Institute Limited | Stabilized photo-alignment layer for liquid crystal |
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