KR102555663B1 - Optical film capable of controlling the order of liquid crystal by UV and heat sensitivity, and smart windows including the same - Google Patents

Abstract

The present invention relates to an active smart window capable of controlling the degree of order of liquid crystals by responding to ultraviolet light and heat. According to this method, it is possible to actively determine the shielding of light, and by diversifying the type of dispersion material used, it is possible to manufacture a smart window that actively responds to various temperature ranges and UV intensities.

Description

Optical film capable of controlling the order of liquid crystal by UV and heat sensitivity, and smart windows including the same}

The present invention relates to an active smart window capable of controlling the order of liquid crystals by sensing ultraviolet light and heat.

The smart window optical film is an optical film that can actively or passively adjust the scattering and reflection of light in response to changes in the surrounding environment or artificial environment. In particular, the liquid crystal-based smart window optical film can reversibly control transmission and scattering by applying an electric field to an optical cell, and based on this, it can perform functions such as indoor temperature control and privacy protection. As a representative example, there is a PDLC (Polymer-Dispersed Liquid Crystal) mode in which liquid crystals are dispersed in fine pores of a certain size in a polymer matrix, scattering occurs, and arranged through application of an electric field to transmit light. In the case of PSCT (Polymer Stabilized Cholesteric Texture), the cholesteric phase is an optical film that uses the fact that it can selectively reflect incident light according to the direction of the rotation axis of the phase. It stabilizes the phase through polymer polymerization and exhibits bistability under specific conditions It is an optical film that can implement light scattering, transmission, selective color reflection, etc. by using properties with In the case of such a typical liquid crystal smart window optical device, it is an optical device that has a scattering state in an initial state and transmits light by external stimuli such as voltage and temperature.

In this regard, Korean Patent Registration No. 2154513 consists of a base unit and a PDLC unit laminated on the rear surface of the base unit, and the base unit is formed by laminating a first polarizing film on the front surface of a transparent substrate, and the PDLC unit is a polymer dispersed liquid crystal. Disclosed is a smart window with improved transparency and visibility comprising a (Polymer Dispersed Liquid Crystal: PDLC) film and a conductive transparent film laminated on both sides of the PDLC film.

However, in the case of current smart windows, when they are actively operated by external stimuli, rather than blocking light in the initial state, they block light according to external stimuli in the state of transmitting light in the initial state, thereby controlling the amount of light, blocking ultraviolet rays, and temperature. It is being developed in a form of regulation. Therefore, types such as the existing PDLC and PSCT are not suitable for active smart windows.

Korean Registered Patent No. 2154513

The present invention controls the phase transition temperature and domain size of the host liquid crystal by maximizing the difference in optical transmittance between transmission and scattering states through changes in external temperature and intensity of an external light source, and diversifying the types of dispersing materials used to provide smart windows. It is intended to provide usable optical films.

In order to solve the above problem,

In one embodiment, the present invention provides a first conductive substrate and a second conductive substrate positioned opposite to each other; and a crystalline host liquid crystal formed between the first conductive substrate and the second conductive substrate, in which an amphiphilic photoisomerization material including mesogen and a photoisomerization material including three isomerizable mesogens are dispersed. Provides an optical film capable of controlling the order of liquid crystals comprising a.

The amphiphilic photoisomerization material including the mesogen may be present at interfaces between the crystalline host liquid crystal and the first conductive substrate and the second conductive substrate.

The optical isomerization material including the three isomerizable mesogens may be present in the bulk of the crystalline host liquid crystal.

The amphiphilic optical isomerization material including the mesogen and the optical isomerization material including the three isomerizable mesogens may each contain 0.1 to 1 wt%.

The crystalline host liquid crystal may include a mixture of a smectic liquid crystal and a chiral dopant.

The crystalline host liquid crystal may include 90% or more of the smectic liquid crystal and 10% or less of the chiral dopant.

The first conductive substrate or the second conductive substrate may be a polymer substrate.

In addition, a smart window including the optical film according to the above and actively determining light shielding according to external temperature and ultraviolet light concentration of an external light source is provided.

Although the conventional smart window optical film has a problem of relying only on passive conversion by an external stimulus such as an electric or magnetic field, the optical film capable of controlling the order of liquid crystals according to the present invention and the smart window including the optical film Depending on the intensity and temperature of the external light source, light shielding can be actively determined. In addition, it is possible to manufacture a smart window that actively responds to various temperature ranges and UV intensities by diversifying the types of dispersion materials used.

In addition, the optical film capable of controlling the order of liquid crystal according to the present invention and the smart window including the optical film convert the liquid crystal into a physical gel so that the driving voltage does not increase significantly even after stabilization. Therefore, it can be used in a variety of ways, such as automobiles, ships, airplanes, etc. in the transportation field, which cannot be used due to problems such as power, and can be applied to various fields due to easy processability.

1 shows the structural formula of the optical isomerization material of the optical film according to the present invention [(a) an amphiphilic optical isomerization material containing mesogen and (b) an optical isomerization material containing three isomerizable mesogens. nitriding material].
Figure 2 is a schematic diagram showing the operating principle of the smart window according to the present invention.
3 illustrates a smart window according to transmission or scattering of light according to an embodiment of the present invention.

Since the present invention can make various changes and have various embodiments, specific embodiments will be illustrated in the drawings and described in detail in the detailed description.

However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

In the present invention, the term "comprises" or "has" is intended to designate that there is a feature, number, step, operation, component, part, or combination thereof described in the specification, but one or more other features It should be understood that the presence or addition of numbers, steps, operations, components, parts, or combinations thereof is not precluded.

Currently, smart window technology is subdivided based on various process methods or principles. Among them, active and passive smart window technologies are divided according to the driving method. Active smart window is a technology that transmits or blocks light through artificial manipulation, and passive smart window is a technology that automatically transmits or blocks light according to the surrounding environment (amount of light, temperature, humidity, etc.). Both technologies have advantages and disadvantages, and are currently used in various ways such as windows and interiors of buildings. However, in the case of passive smart windows, energy consumption is very high, and active smart window technology has a disadvantage that artificial manipulation is impossible. Therefore, the present invention combines the advantages of the following technologies, and is an active smart window that changes by the surrounding environment when not operated, but can be operated like a passive smart window, as well as liquid crystal in the case of a polymer dispersed liquid crystal in an existing passive smart window. There was a phenomenon in which the driving voltage rose very high due to the interaction between the polymer and the polymer, but in the present invention, the driving voltage does not increase significantly even after stabilization by converting the liquid crystal into a physical gel instead of the polymer, which is the above problem. may not be Therefore, it can be used in a variety of ways, such as automobiles, ships, airplanes, etc. in the transportation field, which cannot be used due to problems such as power, and can be applied to various fields due to easy processability.

Hereinafter, the present invention will be described in detail.

The present invention, a first conductive substrate and a second conductive substrate positioned opposite to each other; and a crystalline form formed between the first conductive substrate and the second conductive substrate, in which an amphiphilic photoisomerization material including mesogen and a photoisomerization material including three isomerizable mesogens are dispersed. It provides an optical film capable of controlling the order of the liquid crystal including; host liquid crystal.

Specifically, the present invention includes a crystalline host liquid crystal formed between a first conductive substrate and a second conductive substrate, a photo-isomerization material dispersed in the crystalline host liquid crystal, and a crystalline host liquid crystal and a conductive substrate (first conductive substrate). The optical isomerization material present at the interface between the conductive substrate and the second conductive substrate) controls the degree of order of the liquid crystal through isomerization of the optical isomerization materials by external ultraviolet rays or heat, so that the transmission and scattering of light can be controlled. there is.

In the optical film, the host liquid crystal uses a liquid crystal having a crystalline phase as a host liquid crystal, and a photoisomerization material capable of inducing vertical alignment by moving to an interface between the host liquid crystal and the conductive substrate and optical isomerism in the host liquid crystal It may be a dispersion of another type of optical isomerization material capable of changing the order of the host liquid crystal through nitration.

The first conductive substrate or the second conductive substrate may be a polymer substrate.

The first conductive substrate or the second conductive substrate can be freely used by selecting a substrate according to the purpose of use among glass, metal, carbon fiber, silicon, and polymer substrates, but in the present invention, a large-area optical film, especially used for smart windows It is preferable to use a polymer substrate for use in the optical film, and more preferably, it may be polyethylene terephthalate, polyacrylate, or polyethylene.

The crystalline host liquid crystal may include a mixture of smectic liquid crystal and a chiral dopant. The smectic liquid crystal and chiral dopant may include a liquid crystal and a chiral dopant having various phase transition temperatures and helical twist power (HTP) according to a desired phase transition temperature range. For example, the smectic liquid crystal may include 4-cyano-4'-octylbiphenyl (8CB), and the chiral dopant is S-(+)-2-octyl 4-(4-hexyloxybenzoyloxy)benzoate (S811 ) may be included.

The crystalline host liquid crystal may include 90% or more of the smectic liquid crystal and 10% or less of the chiral dopant. For example, the crystalline host liquid crystal may include 90 to 99% of a smectic liquid crystal and 1 to 10% of a chiral dopant.

When the surface material and the dispersed material in the liquid crystal are isomerized in the host liquid crystal by external ultraviolet light, the order degree of the crystalline host liquid crystal is greatly changed, making the domain size of the liquid crystal small and changing the phase to a liquid crystal phase, thereby generating strong light It is possible to manufacture an optical film that can be used in a variable light transmission device capable of controlling transmission and scattering of light by inducing scattering.

The optical isomerization material dispersed in the crystalline host liquid crystal and present at the interfaces of the crystalline host liquid crystal and the first conductive substrate and the second conductive substrate to induce homeotropic alignment is an amphiphilic light containing mesogen. It may be an isomerizing material.

The optical isomerization material dispersed in the crystalline host liquid crystal and present in the bulk of the crystalline host liquid crystal to change the order degree of the crystalline host liquid crystal may be an optical isomerization material containing three isomerizable mesogens. can

The amphiphilic optical isomerization material including the mesogen and the optical isomerization material including the three isomerizable mesogens may each contain 0.1 to 1 wt%.

1 shows the structural formula of the optical isomerization material of the optical film according to the present invention.

(a) of FIG. 1 is a structural formula of the amphiphilic optical isomerization material containing the mesogen, and the mesogen moiety (M) is not limited to its type as long as it is a material capable of optical isomerization, but, for example, azobenzene ( azobenzene) may be included.

1(b) is a structural formula of the optical isomerization material including the three isomerizable mesogens, has a C3 symmetric structure, and each branch includes an isomerizable mesogen moiety. For example, the mesogen moiety M may include various optical isomers according to external light source conditions of the region where the optical film is used, and may include azobenzene, but is not limited thereto.

The amphiphilic photoisomerization material containing the mesogen moves to the surface of the crystalline host liquid crystal (the interface between the crystalline host liquid crystal and the first conductive substrate and the second conductive substrate) to induce homeotropic alignment of the liquid crystal phase. When isomerization is caused by external ultraviolet rays, it is a material that can change the surface energy and change back to horizontal orientation. When this material is used, monodomains are formed because the initial crystalline liquid crystals are vertically arranged in the entire area, and optically, light scattering is not caused, so that a transparent state is maintained. At this time, when the amphiphilic photoisomerization material including mesogen is isomerized by an external light source, the surface energy changes and the liquid crystal becomes horizontally aligned. do. However, at this time, the degree of light scattering is not very large because the optical axis of the liquid crystal is randomly formed in a two-dimensional plane.

Therefore, in order to form the optical axis of the crystalline host liquid crystal in a disorderly manner in a three-dimensional space, light including the three isomerizable mesogens as another type of light-reactive material capable of changing the orientation of the liquid crystal in the bulk Isomerization materials can be mixed.

The photoisomerization material including the three isomerizable mesogens is mixed in the liquid crystal without moving to the surface, and when photoisomerization occurs by external ultraviolet rays, the order of the surrounding liquid crystal layer is reduced. The optical axis of the multi-domain liquid crystal, which exists disorderly in a two-dimensional plane, can be disordered in a three-dimensional space. Based on this, the host liquid crystal forms multi-domains that are randomly distributed in a three-dimensional space, and thus has a characteristic that light scattering is very high. Therefore, it is possible to manufacture an optical film capable of actively controlling the amount of light entering from the outside by changing the degree of order of the liquid crystal according to the amount of external ultraviolet light.

In addition, the thermotropic liquid crystal used as the host liquid crystal may cause a phase transition from a smectic liquid crystal phase having high crystallinity to a nematic liquid crystal having a lower crystallinity as the temperature rises, and at this time, the chiral liquid crystal contained in the host liquid crystal A degree of disorder is generated by the dopant and the photoisomerization material to form multi-domains, so that multi-domains can be formed by temperature even in the absence of light. Based on this, the degree of light scattering can be adjusted not only with an external light source but also with external temperature changes.

Since the optical film according to the present invention is a mechanism for adjusting the degree of light scattering by adjusting the size of the domain by controlling the degree of order of the host liquid crystal, the type of usable dispersion material is not limited to the liquid crystal system, and the process process is very Since it is simple, it is possible to easily proceed with process optimization and large-area expansion.

In addition, a smart window including the optical film according to the above and actively determining light shielding according to external temperature and ultraviolet light concentration of an external light source is provided.

The smart window according to the present invention includes the optical film, so that transmission and blocking of light can be controlled.

Specifically, the amount of light can be controlled by changing the degree of order of the liquid crystal by causing isomerization of light-reactive materials dispersed in the host liquid crystal. In addition, a degree of disorder is generated by the chiral dopant and the photoisomerization material included in the host liquid crystal, thereby forming a multi-domain by temperature even in the absence of light, so that not only the external light source but also the external temperature The degree of light scattering can be adjusted even with the change.

The smart window may be a smart window that actively determines the shielding of light according to the type and light sensitivity of the dispersion material used in the optical film and the concentration of ultraviolet light of an external light source, and transmits light in the initial state. You can make smart windows.

Figure 2 is a schematic diagram showing the operating principle of the smart window according to the present invention.

As shown in FIG. 2, the smart window is an active smart window that determines transmission and shielding of light by simultaneously adjusting the phase shift and orientation characteristics of liquid crystals. At room temperature, which is a general condition, at an appropriate level of ultraviolet light, the external light can be transmitted, and the internal temperature can be controlled.

In an initial state, a chiral smectic liquid crystal, which is a host liquid crystal, forms a monodomain in a vertically aligned state by an amphiphilic photoisomerization material containing a mesogen for controlling the orientation of the liquid crystal on the substrate surface. It transmits light without scattering and maintains a transparent state. The condition at this time is when an external light source does not include a large amount of ultraviolet rays and the external temperature is within 25 to 30 ° C. so that the isomerization of the amphiphilic photoisomerization material containing mesogen does not occur. In this initial state, when the external ultraviolet rays become stronger while the external temperature is maintained at 25 to 30 ° C, the amphiphilic photoisomerization material including mesogen contained in the liquid crystal substrate and the 3 A photo-isomerization material containing two isomerizable mesogens causes isomerization, and the host liquid crystal, which was oriented in a monodomain in a fixed state (chiral smectic) of the liquid crystal, is formed into a small multi-domain to reduce light scattering. By induction, it becomes an opaque state (right figure in Fig. 2).

Again, in the initial state, external ultraviolet rays are not strong, but when the temperature rises and exceeds 30 ° C, the host liquid crystal in the chiral smectic state undergoes a phase transition and is converted to a focal state, thereby forming a cholesteric liquid crystal domain. It is randomly formed, and the external light source becomes a state in which scattering occurs. Therefore, it is possible to block the external light source in an opaque state and prevent the temperature inside the room from rising (left drawing of FIG. 2).

The mesogen-containing amphiphilic optical isomerization material may include a material represented by Chemical Formula 1 below.

[Formula 1]

The optical isomerization material including the three isomerizable mesogens may include a material represented by Chemical Formula 2 below.

[Formula 2]

In Formula 2, R includes a substance represented by Formula 3 below.

[Formula 3]

Hereinafter, the present invention will be described in more detail through examples and the like according to the present invention, but the scope of the present invention is not limited by the examples presented below.

[Example]

A host liquid crystal mixture was prepared by mixing a chiral dopant (S811) and smectic liquid crystal (8CB) in a weight ratio of 9:1. In addition, 0.1 to 1 wt% of the amphiphilic azobenzene alignment material (Formula 1 above) for adjusting the alignment of liquid crystals on the surface of the substrate, isomerization for adjusting the alignment of liquid crystals in the bulk of the liquid crystal and stabilizing the phase A mixture was prepared by mixing an azobenzene material (Formula 2) in an amount of 0.1 to 1 wt% of the host liquid crystal.

When the prepared liquid crystal mixture is injected into an optical cell formed with a cell gap of 10 to 30 μm and stabilized, the chiral smectic liquid crystal is vertically aligned at room temperature, and at this time, light is transmitted [Fig. see a)]. When the temperature rises in the absence of external ultraviolet rays, the smectic liquid crystal phase undergoes a phase transition to the chiral nematic liquid crystal phase and forms a focal conic phase. At this time, light is scattered by the disorderly located liquid crystal domains [ See (b) of FIG. 3]. In addition, when only ultraviolet rays are irradiated at a low temperature, azobenzene compounds inside the cell are isomerized by ultraviolet rays, increasing the order of the chiral smectic liquid crystal phase, forming small domains, and inducing scattering of light. state [see (c) of FIG. 3].

Claims (8)

a first conductive substrate and a second conductive substrate positioned opposite to each other; and
A crystalline host liquid crystal formed between the first conductive substrate and the second conductive substrate and in which an amphiphilic photoisomerization material including mesogen and a photoisomerization material including three isomerizable mesogens are dispersed; include,
The crystalline host liquid crystal includes a mixture of a smectic liquid crystal and a chiral dopant,
The amphiphilic optical isomerization material including the mesogen and the optical isomerization material including the three isomerizable mesogens are isomerized by external ultraviolet rays to disorder the optical axis of the crystalline host liquid crystal, thereby increasing the light scattering degree. As it rises, it becomes opaque,
A phase change occurs from the smectic liquid crystal having high crystallinity to a nematic liquid crystal having a lower crystallinity by external heat, and at this time, the degree of disorder is generated by the chiral dopant and the optical isomerization materials, thereby increasing the degree of light scattering. As a result, it becomes opaque,
An optical film capable of controlling the order of liquid crystals that actively controls the amount of light coming from the outside by controlling the order of liquid crystals through isomerization of photo-isomerization materials by external ultraviolet light or heat.
According to claim 1,
The amphiphilic optical isomerization material containing the mesogen,
An optical film capable of controlling the order of the liquid crystal, characterized in that present at the interface between the crystalline host liquid crystal and the first conductive substrate and the second conductive substrate.
According to claim 1,
The optical isomerization material containing the three isomerizable mesogens,
An optical film capable of controlling the order of the liquid crystal, characterized in that present in the bulk of the crystalline host liquid crystal.
According to claim 1,
The amphiphilic optical isomerization material including the mesogen and the optical isomerization material including the three isomerizable mesogens each contain 0.1 to 1 wt% of an optical film capable of controlling the order of liquid crystal. .
delete According to claim 1,
The crystalline host liquid crystal comprises 90% or more of the smectic liquid crystal and 10% or less of the chiral dopant.
According to claim 1,
The first conductive substrate or the second conductive substrate is an optical film capable of controlling the order of liquid crystal, characterized in that the polymer substrate.
Including the optical film according to any one of claims 1 to 4, 6 and 7,
A smart window that actively determines the shielding of light according to the outside temperature and the UV concentration of the external light source.