A method for preparing a liquid crystal polarization holographic device

Abstract

The application provides a preparation method of a liquid crystal polarization holographic device, and the method comprises the step of forming a liquid crystal film on a substrate by vacuum evaporation. The step of vacuum evaporation comprises: liquefying and atomizing an evaporation material, then gasifying the evaporation material to obtain an evaporation material mixed gas; introducing the evaporation material mixed gas into a film plating cavity, so that the evaporation material mixed gas condenses on the substrate to form a liquid crystal film, and then irradiating the liquid crystal film with ultraviolet light for curing. The application adopts vacuum film plating, and the method does not need a solvent, can form a liquid crystal polarization holographic device based on optical orientation with a multi-layer structure and a continuous gradient structure, and eliminates the crosstalk problem between the multi-layer liquid crystal films.

Description

Technical Field

[0001] This invention relates to the field of optical experimental technology, and in particular to a method for fabricating a liquid crystal polarization holographic device. Background Technology

[0002] Liquid crystal polarization holographic devices are optical devices formed using a photoalignment layer and liquid crystal self-assembly. The photoalignment layer is composed of a photoalignment material, typically elongated photoalignment molecules based on azo groups. These molecules absorb specific wavelengths of light and rearrange themselves to the direction of lowest energy, generally perpendicular to the long axis of linearly or ellipsometrically polarized light. After the photoalignment layer records a pattern, liquid crystal molecules are placed on top of it using various methods. Due to the interaction between the liquid crystal molecules and the photoalignment molecules, the liquid crystal molecules in direct contact with the photoalignment layer align according to the pattern of the photoalignment layer. The liquid crystal molecules further up align according to the self-assembly characteristics of the liquid crystal itself. Generally, if the liquid crystal is nematic and chiral, the resulting polarization holographic device is transmissive; if the liquid crystal is chiral nematic and its spontaneously formed liquid crystal pitch is close to the wavelength of visible light, a reflective polarization holographic device will be formed.

[0003] Existing liquid crystal coating methods for liquid crystal polarization holographic devices are basically divided into two types: directly filling the empty cell with liquid crystal material using capillary action, or coating a liquid crystal polymer monomer solution onto a photoalignment layer. After the solvent evaporates, since the ambient temperature is generally lower than the crystallization temperature of the heating process but higher than the crystallization temperature of the cooling process, the remaining liquid crystal will briefly form a liquid crystal phase. Solidifying this phase before it crystallizes can form a stable liquid crystal film. However, filling the empty cell is completely impractical for fabricating multilayer liquid crystal structures. Furthermore, solution-based coating methods have a fatal flaw: coating a new layer of solution onto the solidified liquid crystal film causes partial dissolution of the original liquid crystal film, resulting in crosstalk and making the final product uncontrollable. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for fabricating a liquid crystal polarization holographic device.

[0005] The present invention provides a method for fabricating a liquid crystal polarization holographic device, including the step of forming a liquid crystal thin film on a substrate by vacuum evaporation.

[0006] This invention employs vacuum deposition, a method that does not require solvents and can form optically oriented liquid crystal polarization holographic devices with multilayer and continuously gradient structures, while eliminating crosstalk problems between multilayer liquid crystal films.

[0007] In some embodiments of the present invention, the vacuum evaporation step includes:

[0008] The vapor deposition material is liquefied and atomized, and then vaporized to obtain a vapor deposition material mixed gas.

[0009] The vapor deposition material mixture gas is introduced into the coating chamber, causing it to condense on the substrate to form a liquid crystal film, and then the liquid crystal film is cured by irradiating it with ultraviolet light.

[0010] More preferably, the liquefaction and atomization are performed in a liquid ultrasonic atomizing device.

[0011] This invention uses a liquid ultrasonic atomization device to improve the gas production rate and eliminate crosstalk problems caused by solvents.

[0012] The above method is suitable for preparing single-layer liquid crystal films if the composition of the vapor deposition material is not changed.

[0013] When the objective is to prepare a liquid crystal thin film with a multilayer structure, the preparation method includes: after forming a thin film using the vacuum deposition method, placing a substrate covered with a thin film in another deposition chamber, performing vacuum deposition again to form a second thin film, and repeating this method until the target multilayer structure is obtained.

[0014] Alternatively, in some embodiments of the present invention, a liquid crystal thin film with a multilayer structure is prepared by means of: after forming a thin film by vacuum deposition, changing the atomization rate of one or more components in the vapor deposition material, performing vacuum deposition again to form thin films with different compositions, and repeating this method until the target multilayer structure is obtained.

[0015] When the objective is to prepare a liquid crystal thin film with a continuously gradient structure, the preparation method includes:

[0016] By placing the same vapor deposition material in multiple vaporization devices, the vaporization rate in the multiple vaporization devices is continuously varied, thereby continuously and dynamically adjusting the gas composition of the vapor deposition material, and forming a continuous gradient structure by vacuum coating.

[0017] In the above technical solution, the vapor deposition material can be any material useful in the preparation of liquid crystal thin films by vapor deposition method, including but not limited to liquid crystal polymers, chiral materials, photoinitiators, solvents that enhance vaporization rate, polymerization inhibitors, and mixtures of the above materials.

[0018] Liquid crystal polymers are formed by polymer monomers through a polymerization process. The polymer monomers can be liquid crystal polymer monomers with terminal diene groups, such as 1,4-di[4'-(3-acryloyloxy-propoxy)-benzoyloxy]-2-methyl-benzene (CAS No. 174063-87-7), benzoic acid-4-[[6-(acetoxy)hexyl]oxy]-2-chloro-4-[[4-[[6-[(1-oxo-2-propen-1-yl)oxy]hexyl]oxy]benzoyl]phenyl ester (CAS No. 335380-15-9), 2-methyl-1,4-phenylene bis(4-(4-(acryloyloxy)butoxy)benzoate (CAS No. 132900-75-5), and p-phenylene bis[4-[6-(acryloyloxy)hexyloxy]benzoate] ester (CAS No. 123864-17-5). 1,4-Bis-[4-(6-Acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (CAS No. 125248-71-7), (4-(((4-(acryloyloxy)butoxy)carbonyl)oxy)benzoic acid 2-methyl-1,4-diphenol ester (CAS No. 187585-64-4); or a mixture of isotropic materials with terminal divinyl groups for forming network polymers (such as ethylene glycol diacrylate) and liquid crystal polymer monomers with terminal monovinyl groups (such as 4-cyanophenyl 4'-(6-acryloyloxyhexyloxy)benzoate (CAS No. 83847-14-7)); or liquid crystal polymer monomers with terminal mercapto and vinyl groups respectively; and other polymer monomers capable of forming polymers and possessing a liquid crystal phase.

[0019] Chiral materials can induce helical structures in liquid crystals. Typical examples include 4-[4-(hexyloxy)benzoyloxy]benzoic acid (R)-2-octyl ester (CAS No. 133676-09-2) and 4-(4-hexyloxybenzoyloxy)benzoic acid-S-(+)-2-octyl ester (CAS No. 87321-20-8). Any other chiral materials capable of inducing spontaneous helices in liquid crystal materials are also included.

[0020] Photoinitiators are used to generate free radicals under UV light to promote the polymerization of liquid crystal polymer materials. Typical examples include α,α-dimethoxy-α-phenylacetophenone (CAS No. 24650-42-8), as well as any substance and mixture that can promote the polymerization of liquid crystal polymer materials.

[0021] Solvents that enhance vaporization rate are used to increase the vaporization rate of vapor-deposited materials and reduce their vaporization temperature. These include toluene, xylene, propylene glycol methyl ether acetate, and any solvent that has good solubility in the solid material of the vapor-deposited material.

[0022] Polymerization inhibitors are used to prevent spontaneous polymerization of vapor-deposited materials during heating. These include 2,5-bis(1,1-dimethylethyl)-1,4-benzenediol, t-butyl-1,4-benzenediol, and 2,6-di-tert-butyl-p-methylphenol.

[0023] The present invention also provides an apparatus for vapor deposition of liquid crystal thin film, comprising a vaporization chamber and a coating chamber connected to each other. The vaporization chamber is provided with a liquid ultrasonic atomizing device at the top and a gas homogenizing device at the bottom. The mixed gas after passing through the gas homogenizing device enters the coating chamber through a connecting device. The coating chamber is provided with a substrate and an ultraviolet light source capable of irradiating the substrate.

[0024] Furthermore, a gas flow rate controller is disposed between the vaporization chamber and the coating chamber to adjust the speed at which gas enters the coating chamber (i.e., the transmission speed).

[0025] Furthermore, both the vaporization chamber and the coating chamber are in a vacuum environment.

[0026] Furthermore, after passing through the gas homogenization device, the mixed gas enters the coating chamber and is then sprayed out by the uniform jetting device onto the substrate.

[0027] This invention provides a method for fabricating liquid crystal polarization holographic devices. By using a solvent-free vapor deposition method, light-oriented liquid crystal polarization holographic devices can be prepared. This method facilitates the formation of thin films with complex structures, improves gas production rate through ultrasonic atomization, eliminates crosstalk problems caused by solvents, and can be used to fabricate liquid crystal polarization holographic devices with multilayer structures and liquid crystal polarization holographic devices with continuously gradient structures.

[0028] This invention provides a method for fabricating a liquid crystal polarization holographic device. Unlike traditional methods that involve filling a cell with liquid crystal material or coating a liquid crystal polymer monomer solution onto a photoalignment layer, this invention uses vacuum evaporation, which does not require solvents. By adjusting the evaporation method, a photoalignment-based liquid crystal polarization holographic device with a multilayer structure and a continuously gradient structure can be formed, and the crosstalk problem between multilayer liquid crystal films can be eliminated. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the apparatus and method for preparing a single-layer liquid crystal film provided by the present invention;

[0030] Figure 2 This is a schematic diagram of the method for preparing multilayer liquid crystal films of different materials provided by the present invention;

[0031] Figure 3 This is a schematic diagram of the method for forming multilayer liquid crystal films with different structures using materials with different ratios provided by the present invention;

[0032] Figure 4 This is a schematic diagram of the method for forming a continuous gradient liquid crystal film provided by the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0034] In this article, the terms "substrate" and "substrate" are used interchangeably.

[0035] Example 1

[0036] This embodiment provides an apparatus for preparing a single-layer liquid crystal thin film, including a vaporization chamber and a coating chamber, such as... Figure 1 As shown, the vaporization chamber is connected to the coating chamber, allowing the vaporized liquid crystal material to pass through.

[0037] The vaporization chamber is a vacuum environment with controllable wall temperature, maintaining a constant temperature during the vaporization of the liquid crystal material. A liquid ultrasonic atomizing device is installed at the top of the vaporization chamber, with controllable and constant temperature, aiming to increase the gas production rate during the liquid crystal material vaporization process. The heated and liquefied liquid crystal material is atomized into small droplets by the ultrasonic atomizing device. A gas homogenizing device is located at the bottom of the vaporization chamber; the vaporized liquid crystal material gas passes through this device and is then fed into the coating chamber via a connecting device.

[0038] After the liquid crystal material gas in the vaporization chamber enters the coating chamber, it is ejected by a uniform jetting device. The coating chamber is a vacuum environment, and the substrate is placed inside (specifically, on a rotatable sample stage) and kept at a constant temperature. The gas contacts the low-temperature substrate and condenses into a liquid crystal film on the substrate. Finally, it is cured by ultraviolet light to complete the preparation of the liquid crystal film.

[0039] Based on the above embodiments, a gas flow rate controller is configured between the vaporization chamber and the coating chamber to adjust the speed at which gas enters the coating chamber (i.e., the transmission speed).

[0040] Example 2

[0041] A liquid crystal polarization holographic device based on optical orientation was fabricated using a vacuum evaporation method, wherein the specific method for forming a single-layer liquid crystal thin film is as follows: Figure 1 As shown, it includes:

[0042] 1. Liquefaction and atomization of vapor deposition materials

[0043] The vapor-deposited material is placed in an ultrasonic atomizing device, which heats the material to liquefy it. The heating temperature is generally greater than 40℃ but less than 200℃. The liquefied vapor-deposited material is then atomized into fine droplets by the atomizing device.

[0044] 2. Directly heat the walls of the vaporization chamber to generate a liquid crystal material mixture gas.

[0045] The vaporization chamber is a low-pressure environment, with a pressure generally less than 100 Pa. The chamber wall is temperature-controlled and is used to rapidly heat the atomized droplets into gas. The temperature is generally higher than 200℃, but should be lower than the decomposition temperature of the vapor-deposited material, generally below 500℃.

[0046] 3. A thin film is formed inside the coating cavity.

[0047] The vaporization mixture in the vaporization chamber enters the coating chamber via a uniform jetting device; the coating chamber should be a vacuum environment. The vaporization mixture contacts a low-temperature substrate, where it condenses to form a thin film. The substrate temperature should be significantly lower than the vaporization temperature of the vaporization material, but it should also be sufficient to ensure that the thin film formed on it possesses a liquid crystal state.

[0048] In some embodiments, a gas flow rate controller may be configured between the vaporization chamber and the coating chamber to adjust the speed at which gas enters the coating chamber.

[0049] 4. UV curable liquid crystal film

[0050] After the film is formed, it is irradiated with ultraviolet light, which enables the film to polymerize and form a stable polymer film.

[0051] Example 3

[0052] Based on the above method for forming a single-layer liquid crystal thin film by vapor deposition, multi-layer thin film structures can be formed using different materials. Specific implementation methods are as follows: Figure 2 As shown (each vaporization chamber contains only one type of vapor deposition material), including:

[0053] According to the method of forming a single-layer liquid crystal film by vapor deposition in Example 2, a thin film 1 (the vapor deposition material is material 1) is first formed on a substrate. Then, the substrate with the thin film 1 is placed in another coating chamber. According to the method of forming a single-layer liquid crystal film by vapor deposition in Example 2, the vapor deposition material 2 is vapor deposited onto the thin film 1, and a multilayer thin film structure with thin film 1 and thin film 2 covered on the substrate is obtained.

[0054] Those skilled in the art will understand that if a substrate covered with thin film 1 and thin film 2 is placed in a new coating chamber, and vaporization material 3 is transferred from the corresponding vaporization chamber, a multilayer thin film structure covered with thin film 1, thin film 2 and thin film 3 can be formed on the substrate. This process can be repeated sequentially.

[0055] Example 4

[0056] Based on the above method for forming a single-layer liquid crystal film by vapor deposition, multilayer film structures with different structures can be formed by adjusting the material ratio. Specific implementation methods are as follows: Figure 3 As shown (the vaporization chamber contains multiple liquid ultrasonic atomizing devices), including:

[0057] According to the method of forming a single-layer liquid crystal film by vapor deposition in Example 2, a film 1 is first formed on a substrate (the vapor deposition materials are mixed in ratio 1), and then the atomization rate of one or more liquid ultrasonic atomizing devices is changed to adjust the ratio of liquid crystal materials after atomization or even vaporization, so that a film 2 is formed on the substrate on which film 1 has been formed in ratio 2.

[0058] Similarly, if the ratio is adjusted to ratio 3, film 3 can continue to be formed, and so on.

[0059] Example 5

[0060] Based on the above method for forming a single-layer liquid crystal film by vapor deposition, a continuous gradient film structure can be formed. The specific implementation method is as follows: Figure 4 As shown.

[0061] In this embodiment, the coating device in Embodiment 1 needs to be improved. After improvement, one coating chamber is connected to multiple gasification devices arranged side by side, and the gas inside the coating chamber is formed by mixing the gases output from the multiple gasification devices. A multi-layer homogenizing device is provided outside the outlet of the gasification device, including multiple perforated plates and a stirring device, which is used to mix the gases output from the multiple gasification devices to make them uniform.

[0062] During the thin film formation process, the gasification rate ratio in each gasification chamber is dynamically changed by altering parameters within the gasification device, such as the frequency and power of the ultrasonic atomizing device and the gasification heating temperature, thereby continuously and dynamically adjusting the gas composition. As the gas composition ratio of the liquid crystal material changes dynamically, the thin film structure changes accordingly, forming a gradient structure thin film.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for fabricating a liquid crystal polarization holographic device, characterized in that, This includes the step of forming a liquid crystal thin film on a substrate using vacuum evaporation; The vacuum evaporation process includes: The vapor deposition material is liquefied and atomized, and then vaporized to obtain a vapor deposition material mixed gas. The vapor deposition material mixture gas is introduced into the coating chamber, causing it to condense on the substrate to form a liquid crystal film, and then the liquid crystal film is cured by irradiating it with ultraviolet light. The liquefaction and atomization are performed in a liquid ultrasonic atomizing device; The vapor deposition material includes a liquid crystal polymer monomer; The liquid crystal polymer monomers are polymerized to form a liquid crystal polymer, wherein the polymer monomers are selected from: liquid crystal polymer monomers with terminal divinyl groups; a mixture of isotropic materials with terminal divinyl groups for forming network polymers and liquid crystal polymer monomers with terminal monovinyl groups; liquid crystal polymer monomers with terminal thiol groups and vinyl groups respectively; and other polymer monomers capable of forming polymers and having a liquid crystal phase.

2. The method for fabricating a liquid crystal polarization holographic device according to claim 1, characterized in that, The liquid crystal thin film has a multilayer structure, and the preparation method includes: after forming a thin film by vacuum deposition, placing a substrate covered with a thin film in another deposition chamber, performing vacuum deposition again to form a second thin film, and repeating this method until the target multilayer structure is obtained.

3. The method for fabricating a liquid crystal polarization holographic device according to claim 1, characterized in that, The liquid crystal film has a multilayer structure, and the preparation method includes: after forming a thin film by vacuum deposition, changing the atomization rate of one or more components in the vapor deposition material, performing vacuum deposition again to form thin films with different compositions, and repeating this method until the target multilayer structure is obtained.

4. The method for fabricating a liquid crystal polarization holographic device according to claim 1, characterized in that, The liquid crystal film has a continuous gradient structure, and the preparation method includes: By placing the same vapor deposition material in multiple vaporization devices, the vaporization rate in the multiple vaporization devices is continuously varied, thereby continuously and dynamically adjusting the gas composition of the vapor deposition material, and forming a continuous gradient structure by vacuum coating.

5. The method for fabricating a liquid crystal polarization holographic device according to any one of claims 1-4, characterized in that, The vapor deposition material also includes one or more of the following: chiral material, photoinitiator, solvent that enhances vaporization rate, and polymerization inhibitor.

6. The method for fabricating a liquid crystal polarization holographic device according to claim 5, characterized in that, The chiral material is a chiral material that enables liquid crystal polymers to generate spontaneous helices.

7. The method for fabricating a liquid crystal polarization holographic device according to claim 5, characterized in that, The chiral material is 4-[4-(hexyloxy)benzoyloxy]benzoic acid (R)-2-octyl ester or 4-(4-hexyloxy)benzoyloxy)benzoic acid-S-(+)-2-octyl ester; And / or, the photoinitiator is α,α-dimethoxy-α-phenylacetophenone; And / or, the solvent for increasing the vaporization rate is one or more of toluene, xylene, and propylene glycol methyl ether acetate; And / or, the polymerization inhibitor is one or more of 2,5-bis(1,1-dimethylethyl)-1,4-benzenediol, t-butyl-1,4-benzenediol, and 2,6-di-tert-butyl-p-methylphenol.

8. An apparatus for vapor deposition of liquid crystal thin films, characterized in that, It includes a vaporization chamber and a coating chamber that are interconnected. The top of the vaporization chamber is equipped with a liquid ultrasonic atomizing device and the bottom is equipped with a gas homogenizing device. The mixed gas after passing through the gas homogenizing device enters the coating chamber through a connecting device. The coating chamber is equipped with a substrate and an ultraviolet light source that can irradiate the substrate. Evaporation materials include liquid crystal polymer monomers; The liquid crystal polymer monomers are polymerized to form a liquid crystal polymer, wherein the polymer monomers are selected from: liquid crystal polymer monomers with terminal divinyl groups; a mixture of isotropic materials with terminal divinyl groups for forming network polymers and liquid crystal polymer monomers with terminal monovinyl groups; liquid crystal polymer monomers with terminal thiol groups and vinyl groups respectively; and other polymer monomers capable of forming polymers and having a liquid crystal phase.

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