Method for preparing microstructure of liquid crystal elastomer based on photopolymerization phase separation

Abstract

The present application relates to a liquid crystal elastomer microstructure preparation method based on photopolymerization phase separation, the method comprising S1, for a first liquid crystal cell with a specified thickness, filling a mixture of photopolymer monomers and liquid crystals between the first substrate and the second substrate of the first liquid crystal cell, the first substrate being a substrate without an alignment layer, and the second substrate being coated with an alignment layer; S2, covering a gray-tone mask on the first surface of the first substrate of the first liquid crystal cell; the first surface of the first substrate being the surface away from the mixture; S3, performing ultraviolet exposure on the gray-tone mask to separate the photopolymer monomers and the liquid crystals, and obtaining a composite structure; S4, based on a pre-configured liquid crystal elastomer prepolymer, processing the composite structure according to a preset liquid crystal elastomer microstructure preparation strategy, and obtaining a liquid crystal elastomer microstructure. The liquid crystal elastomer microstructure film prepared by the method has a thickness ranging from several microns to tens of microns, good alignment, and simple manufacturing process, low cost and high precision.

Description

Technical Field

[0001] This invention relates to the field of liquid crystal elastomer microstructure preparation technology, and in particular to a method for preparing liquid crystal elastomer microstructures based on photopolymerization phase separation. Background Technology

[0002] In recent years, with the development of science and technology, liquid crystal elastomers, as a smart material that combines the orderliness of liquid crystals and the elasticity of elastomers, can respond to various external stimuli such as heat, light, electricity, magnetism, and humidity. They can be miniaturized, remotely controlled without contact, and their deformation can be arbitrarily set based on orientation, making them promising for applications.

[0003] Currently, common methods for fabricating liquid crystal elastomer (LCD) microstructures include soft lithography combined with magnetic field alignment, 4D printing, and self-assembly. Soft lithography combined with magnetic field alignment involves fabricating silicon microstructure arrays using photolithography and etching techniques. After molding, the LCD prepolymer is poured into a PDMS mold, and orientation is achieved using a magnetic field. Photopolymerization occurs at its nematic phase temperature, and finally, the PDMS is peeled off to obtain the LCD microstructure. This method requires photolithography and etching, as well as a large magnetic field for alignment, resulting in bulky equipment, complex steps, high costs, and limited finished product orientation, failing to achieve complex orientations. 4D printing utilizes the shear force during LCD extrusion for alignment or uses lasers and ultraviolet light for point-by-point and layer-by-layer printing. It primarily fabricates individual LCD microactuators and rarely fabricates surface microstructure arrays. It suffers from slow printing speeds, making mass production and large-area sample fabrication impossible, large and expensive equipment, long processing times, and limited applications. Self-assembly includes self-assembled structures formed on the surface of liquid crystal elastomer materials and soft imprinting using other self-assembly materials. However, it suffers from the drawback of having a single morphology of microstructures, which is limited by the materials and structures of self-assembly and cannot be arbitrarily designed. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a method for preparing liquid crystal elastomer microstructures based on photopolymerization phase separation, which solves the technical problems of high cost, low precision, difficulty in mass production, and difficulty in large-area preparation of liquid crystal elastomer microstructures in the prior art.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing liquid crystal elastomer microstructures based on photopolymerization phase separation, comprising:

[0008] S1. For a first liquid crystal cell of a specified thickness, a mixture of photopolymer monomer and liquid crystal is filled between a first substrate and a second substrate of the first liquid crystal cell. The first substrate is an upper substrate without an alignment layer, the second substrate is a lower substrate, and an alignment layer is coated on the first surface of the second substrate facing the mixture.

[0009] S2. A grayscale mask is applied to the first surface of the first substrate of the first liquid crystal cell; the first surface of the first substrate is the surface away from the mixture.

[0010] S3. Expose the grayscale mask to ultraviolet light until the photopolymer monomers and liquid crystals are completely separated, and the photopolymer monomers are aggregated on the second side of the first substrate to form a polymer microstructure film, and the liquid crystals are aggregated on the first side of the second substrate to obtain a composite structure.

[0011] S4. Based on the pre-configured liquid crystal elastomer prepolymer, the composite structure is processed according to the preset liquid crystal elastomer microstructure preparation strategy to obtain the liquid crystal elastomer microstructure.

[0012] Optionally, S4 includes:

[0013] S41. A first substrate in which a polymer microstructure film is aggregated in a composite structure is pretreated to obtain a third substrate, wherein the polymer microstructure film aggregated on the second side of the third substrate has an orientation layer.

[0014] S42. A second liquid crystal cell is formed using a third substrate and a fourth substrate; a liquid crystal elastomer prepolymer is filled between the third substrate and the fourth substrate of the second liquid crystal cell; an alignment layer is provided on the first side of the fourth substrate facing the liquid crystal elastomer prepolymer, and the second side of the third substrate faces the liquid crystal elastomer prepolymer.

[0015] S43. Expose the first surface of the third substrate of the second liquid crystal cell to ultraviolet light until the liquid crystal elastomer prepolymer is polymerized and cured;

[0016] S44. The polymerized and cured liquid crystal elastomer prepolymer is peeled off from the second liquid crystal cell to obtain the liquid crystal elastomer microstructure.

[0017] Optionally, S41 includes:

[0018] S41-1. The first substrate in the composite structure is cleaned, dried and subjected to ultraviolet ozone hydrophilic treatment.

[0019] S41-2. Spin-coat the first substrate after hydrophilic treatment with a polyvinyl alcohol aqueous solution and dry it.

[0020] S41-3. The dried first substrate is rubbed to form an orientation layer on the surface of the polymer microstructure film on the first substrate, thus obtaining the third substrate.

[0021] Optionally, S4 includes:

[0022] S41' Clean the composite structure until all the liquid crystal in the composite structure is washed out;

[0023] S42' Fill the cleaned composite structure with a pre-configured liquid crystal elastomer prepolymer to obtain a third liquid crystal cell; the third liquid crystal cell includes a first substrate, a second substrate and a liquid crystal elastomer prepolymer filled between the first substrate and the second substrate;

[0024] S43', The first surface of the first substrate of the third liquid crystal cell is exposed to ultraviolet light until the liquid crystal elastomer prepolymer is polymerized and cured;

[0025] S44': The polymerized and cured liquid crystal elastomer prepolymer is peeled off from the second liquid crystal cell to obtain the liquid crystal elastomer microstructure.

[0026] Optionally, the pre-configured liquid crystal elastomer prepolymer includes a liquid crystal polymer monomer, a crosslinking agent, and a photoinitiator;

[0027] The molar fraction of the liquid crystal polymer monomer is 60 mol%-80 mol%.

[0028] The molar fraction of the crosslinking agent is 15 mol%-30 mol%.

[0029] The molar fraction of the photoinitiator is 1 mol-5 mol%.

[0030] Optionally, during the ultraviolet exposure of the grayscale mask in S3, the temperature of the mixture of photopolymer monomer and liquid crystal remains stable at 100±10℃.

[0031] Optionally, the ultraviolet light intensity for ultraviolet exposure of the grayscale mask is 0.4-0.8 mW / cm². 2 The exposure time is 20-40 minutes.

[0032] Secondly, the present invention also provides another method for preparing liquid crystal elastomer microstructures based on photopolymerization phase separation, comprising:

[0033] A1. For a fourth liquid crystal cell of a specified thickness, a mixture of liquid crystal elastomer prepolymer and liquid crystal is filled between the fifth and sixth substrates of the fourth liquid crystal cell, and an alignment layer is coated on the second side of the fifth substrate and the first side of the sixth substrate; the fifth substrate is the upper substrate and the sixth substrate is the lower substrate; the second side of the fifth substrate and the first side of the sixth substrate both face the mixture.

[0034] A2. A grayscale mask is applied to the first surface of the fifth substrate of the fourth liquid crystal cell; the first surface of the fifth substrate is the surface away from the mixture.

[0035] A3. Expose the grayscale mask to ultraviolet light until the liquid crystal elastomer prepolymer and liquid crystal are completely separated, and the liquid crystal elastomer prepolymer is aggregated on the second side of the fifth substrate to form a liquid crystal elastomer microstructure, and the liquid crystal is aggregated on the first side of the sixth substrate.

[0036] A4. Peel the liquid crystal elastomer microstructure from the fourth liquid crystal cell to obtain the liquid crystal elastomer microstructure.

[0037] Optionally, in the mixture of liquid crystal elastomer prepolymer and liquid crystal, the mass ratio of liquid crystal elastomer prepolymer to liquid crystal is 1:1.

[0038] Thirdly, it also includes a liquid crystal elastomer microstructure formed by any of the preparation methods described in the first and second aspects above.

[0039] (III) Beneficial Effects

[0040] This invention proposes a method for preparing liquid crystal elastomer microstructures based on photopolymerization phase separation. It can combine photopolymerization phase separation technology with ultraviolet exposure to prepare liquid crystal elastomer microstructure arrays. The preparation method and equipment are simple, the steps are concise, and the cost is low.

[0041] By combining liquid crystal cell fabrication technology, well-aligned liquid crystal elastomer microstructure arrays with thicknesses ranging from a few micrometers to tens of micrometers can be fabricated with structural precision down to the micrometer level. By adjusting the sizes of the liquid crystal cell, grayscale mask, and ultraviolet exposure light source, large-area fabrication and mass production in multiple specifications can be achieved.

[0042] The method proposed in this invention can also adjust the polymer microstructure attached to the substrate by adjusting the grayscale gradient and distribution of the grayscale mask, thereby realizing various different surface morphologies such as lenses and gratings. It has broad application prospects and can be used in thermally / optically tunable optical devices. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of a method for preparing liquid crystal elastomer microstructures based on photopolymerization phase separation, according to an embodiment of the present invention.

[0044] Figure 2 This is a schematic diagram of another method for preparing liquid crystal elastomer microstructures based on photopolymerization phase separation, provided in an embodiment of the present invention.

[0045] Figure 3 for Figure 1 A schematic diagram of the liquid crystal elastomer microstructure fabrication process provided in one embodiment;

[0046] Figure 4 (a) is an optical microscopic image of a liquid crystal elastomer micropillar lens array prepared in one embodiment;

[0047] Figure 4 (b) is Figure 4 Polarization optical microscopy image of the liquid crystal elastomer micropillar lens array prepared in embodiment (a) with the analyzer oriented at a 0° angle;

[0048] Figure 4 (c) is Figure 4 Polarization optical microscopy image of the liquid crystal elastomer micropillar lens array prepared in embodiment (a) with the analyzer oriented at a 45° angle;

[0049] Figure 4 (d) is Figure 4 White light interference image and schematic diagram of the cross-sectional sagitta of the liquid crystal elastomer micropillar lens array prepared in embodiment (a);

[0050] Figure 5 (a) is a schematic diagram comparing the focusing effect of the liquid crystal elastomer micropillar lens array provided in one embodiment when the incident polarized light is parallel to the direction of the liquid crystal elastomer micropillar lens at 20°C and 260°C.

[0051] Figure 5 (b) is Figure 5 (a) A schematic diagram comparing the focusing effect of the liquid crystal elastomer micropillar lens array provided in embodiment (a) when the incident polarized light is perpendicular to the direction of the liquid crystal elastomer micropillar lens at 20°C and 260°C.

[0052] Figure 6 (a) is an optical micrograph of a liquid crystal elastomer microstructure provided in another embodiment;

[0053] Figure 6 (b) is Figure 6 Polarized optical microscopy image of the liquid crystal elastomer microstructure at a 0° angle provided in embodiment (a);

[0054] Figure 6 (c) is Figure 6 Polarized optical micrograph of the liquid crystal elastomer microstructure provided in embodiment (a) at a 45° angle;

[0055] Figure 6 (d) is Figure 6 The white light interference image of the liquid crystal elastomer microstructure and a schematic diagram of its cross-sectional sag provided in embodiment (a);

[0056] Figure 6 (e) is Figure 6 An optical micrograph of the liquid crystal elastomer microstructure and a schematic diagram of the focusing effect in the region provided in embodiment (a);

[0057] Figure 6 (f) is Figure 6 A schematic diagram of the incident light polarization parallel to the orientation direction provided in embodiment (a) of the liquid crystal elastomer microstructure;

[0058] Figure 6 (g) is Figure 6 A schematic diagram of the incident light polarization perpendicular to the orientation direction of the liquid crystal elastomer microstructure provided in one embodiment of (a);

[0059] Figure 7 for Figure 1 A schematic diagram of the liquid crystal elastomer microstructure fabrication process provided in another embodiment;

[0060] Figure 8 for Figure 2 A schematic diagram of the liquid crystal elastomer microstructure fabrication process provided in one embodiment. Detailed Implementation

[0061] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0062] In recent years, smart materials, due to their ability to sense and respond to external stimuli, have been widely used in fields such as sensors, actuators, artificial muscles, and soft robots. Liquid crystal elastomers, as a type of smart material that combines the orderliness of liquid crystals and the elasticity of elastomers, can respond to various external stimuli such as heat, light, electricity, magnetism, and humidity. They possess advantages such as miniaturization, remote contactless light control, and arbitrary design of deformation based on orientation. They show promising application prospects in biomimetic fields such as tunable structural colors and controllable hydrophilic / hydrophobic and adhesive smart surfaces, tunable optical devices, adaptive photonics, and intelligent soft robots.

[0063] Liquid crystal elastomers exhibit the anisotropy of liquid crystals. Their reversible deformation mechanism involves a temperature increase causing the molecular arrangement to change from a nematic phase to an isotropic state. Macroscopically, this manifests as the sample shrinking along the orientation direction and elongating perpendicular to it. Current technologies based on liquid crystal cell technology employ surface orientation methods such as rubbing and photo-orientation for liquid crystal elastomers. Their shapes are limited to films of tens of micrometers in diameter, mostly producing two-dimensional to three-dimensional stimulus-response deformation. While mechanically stretched liquid crystal elastomers can achieve three-dimensional structure fabrication, their dimensions are mostly in the millimeter or even centimeter range, resulting in low precision. For some special applications, such as light-controlled biomimetic aircraft or swimming robots whose mechanical behavior is influenced by surface microstructures, micrometer-scale three-dimensional liquid crystal elastomer microstructure arrays are typically required, which traditional processing techniques cannot meet. Emerging technologies such as soft lithography and 4D printing can fabricate micrometer-scale high-precision liquid crystal elastomer microstructure arrays, but these are costly to implement.

[0064] Existing technologies for preparing liquid crystal elastomer microstructures suffer from problems such as low fabrication precision, high manufacturing costs, and cumbersome processes, limiting the mass production of liquid crystal elastomer microstructure arrays. Therefore, this invention provides a method for preparing liquid crystal elastomer microstructures based on photopolymerization phase separation, such as... Figure 1 As shown, the methods mainly include:

[0065] S1. For a first liquid crystal cell of a specified thickness, a mixture of photopolymer monomer and liquid crystal is filled between a first substrate and a second substrate of the first liquid crystal cell. The first substrate is an upper substrate without an alignment layer, the second substrate is a lower substrate, and an alignment layer is coated on the first surface of the second substrate facing the mixture.

[0066] S2. A grayscale mask is applied to the first surface of the first substrate of the first liquid crystal cell; the first surface of the first substrate is the surface away from the mixture.

[0067] S3. Expose the grayscale mask to ultraviolet light (using the grayscale mask for gradient ultraviolet exposure) until the photopolymer monomers and liquid crystals are completely separated, and the photopolymer monomers are aggregated on the second side of the first substrate to form a polymer microstructure film, and the liquid crystals are aggregated on the first side of the second substrate to obtain a composite structure.

[0068] The composite structure does not include a grayscale mask, which is removed immediately after ultraviolet exposure in S3.

[0069] S4. Based on the pre-configured liquid crystal elastomer prepolymer, the composite structure is processed according to the preset liquid crystal elastomer microstructure preparation strategy to obtain the liquid crystal elastomer microstructure.

[0070] The grayscale mask is pre-set with grayscale information about the liquid crystal elastomer microstructure. This pre-set grayscale information directly affects the surface morphology of the resulting polymer. Different grayscale values ​​cause differences in light transmittance, which in turn affects the rate of photopolymerization at different locations, leading to lateral diffusion and accumulation of polymer monomers, thus forming different polymer microstructures. Therefore, various microstructure arrays such as lenses and gratings can be fabricated based on the mask design. Thus, the grayscale mask should be determined and designed according to actual needs.

[0071] In some embodiments, in step S3, a gradient ultraviolet exposure is performed on a first liquid crystal cell filled with a mixture using a grayscale mask pre-programmed with grayscale information of the target liquid crystal elastomer microstructure, so that a polymer microstructure film is formed on the substrate of the first liquid crystal cell near the ultraviolet light source. When performing ultraviolet exposure on the first liquid crystal cell filled with the mixture, the temperature of the mixture of photopolymer monomer and liquid crystal is preferably 100±10℃, and the ultraviolet light intensity is 0.4-0.8 mW / cm². 2 The optimal exposure time is 20-40 minutes.

[0072] In practical applications, the mixture filling the first liquid crystal cell can be liquid crystal E7 and UV-curable adhesive NOA65 in a mass ratio of 1:1, wherein the UV-curable adhesive NOA65 contains photopolymer monomers and photoinitiators.

[0073] During ultraviolet (UV) exposure, the substrate coated with the alignment layer is positioned away from the UV light source, while the substrate without the alignment layer is positioned closer to it. The photopolymer monomers gradually polymerize during UV exposure and move closer to the substrate without the alignment layer, causing phase separation between the polymer and the liquid crystal. The liquid crystal then aggregates on the substrate with the alignment layer, ultimately resulting in a composite structure where the polymer microstructure film and the liquid crystal phase are separated. Once polymerization is complete, the polymer microstructure film adheres to the inner surface of the liquid crystal cell substrate.

[0074] In one embodiment, the above method is specifically implemented as follows:

[0075] S31. A grayscale mask with grayscale information of the target liquid crystal elastomer microstructure is attached tightly to the outer surface of the substrate of the first liquid crystal cell without an alignment layer. Here, the outer surface is the substrate surface of the first liquid crystal cell without an alignment layer and far away from the mixture of photopolymer monomer and liquid crystal, i.e., the first surface of the first substrate.

[0076] In this embodiment, both substrates of the first liquid crystal cell are 2.5cm×2.5cm glass substrates. After ultrasonic cleaning, one of them is oriented and coated with an orientation layer. Specifically, after hydrophilic treatment, a 1% polyvinyl alcohol (PVA) aqueous solution is spin-coated as the orientation layer at a speed of 3000 rpm for 30 seconds. After baking at 70°C for 40 minutes, it is rubbed and oriented at a speed of 1000 rpm.

[0077] A first liquid crystal cell with a fixed unidirectional alignment thickness is formed by combining a substrate coated with an alignment layer and another substrate without alignment treatment. The cell thickness is controlled by microspheres with a diameter of 15 μm. In this application, the cell thickness of the liquid crystal cell should be determined by multiple identical microspheres according to the actual required thickness, and this is not a limitation.

[0078] S32. The first liquid crystal cell is placed under an ultraviolet light source for gradient ultraviolet exposure, with the side of the glass substrate coated with the alignment layer away from the ultraviolet light source, so that a polymer microstructure film is formed on the inner surface of the substrate of the first liquid crystal cell near the ultraviolet light source. Here, the inner surface is the surface of the substrate of the first liquid crystal cell that is not coated with the alignment layer and is in contact with the mixture of photopolymer monomers and liquid crystal.

[0079] In this embodiment, the photomask contains grayscale information of the target cylindrical lens array with a period of 200 μm. In step S32, when the first liquid crystal cell is placed under an ultraviolet light source for gradient ultraviolet exposure, the preferred temperature is 100°C and the preferred light intensity is 0.6 mW / cm². 2 The preferred exposure time is 30 minutes.

[0080] Figure 3 This is a flowchart illustrating one embodiment, such as... Figure 3 As shown, in this embodiment, S4 is specifically implemented as follows:

[0081] S41. A first substrate in which a polymer microstructure film is aggregated in a composite structure is pretreated to obtain a third substrate, wherein the polymer microstructure film aggregated on the second side of the third substrate has an orientation layer.

[0082] S42. A second liquid crystal cell is formed using a third substrate and a fourth substrate; a liquid crystal elastomer prepolymer is filled between the third substrate and the fourth substrate of the second liquid crystal cell; an alignment layer is provided on the first side of the fourth substrate facing the liquid crystal elastomer prepolymer, and the second side of the third substrate faces the liquid crystal elastomer prepolymer.

[0083] S43. Expose the first surface of the third substrate of the second liquid crystal cell to ultraviolet light until the liquid crystal elastomer prepolymer is polymerized and cured.

[0084] S44. The polymerized and cured liquid crystal elastomer prepolymer is peeled off from the second liquid crystal cell to obtain the liquid crystal elastomer microstructure.

[0085] Specifically, S41 can be implemented as follows:

[0086] S41-1, Disassemble the composite structure, and clean, dry and treat the first substrate with the grayscale mask removed with ultraviolet ozone hydrophilic treatment; in this embodiment, ethanol is used to wash away the residual liquid crystal.

[0087] S41-2. Spin-coat the first substrate after hydrophilic treatment with a polyvinyl alcohol aqueous solution and dry it; specifically, it can be implemented by spin-coating the first substrate with a 1% polyvinyl alcohol PVA aqueous solution, preferably at a rotation speed of 3000 rpm, preferably at a spin-coating time of 30 s, and baking at 70°C for 40 min.

[0088] S41-3. The dried first substrate is rubbed to align it, forming an alignment layer on the surface of the polymer microstructure film on the first substrate, thus obtaining the third substrate. To avoid damaging the surface structure, the rotation speed of the rubbing alignment is controlled at 600 rpm.

[0089] In one embodiment, a liquid crystal elastomer prepolymer is filled between the third and fourth substrates of the second liquid crystal cell. The liquid crystal elastomer prepolymer contains a mixture of liquid crystal polymer monomer RM006, crosslinking agent RM82, and photoinitiator 651 before being poured into the second liquid crystal cell. Specifically, the temperature is not lower than 90°C when the liquid crystal elastomer prepolymer is poured into the second liquid crystal cell.

[0090] In this embodiment, the thickness of the second liquid crystal cell is preferably 30 μm, the molar fraction of the liquid crystal polymer monomer RM006 is preferably 78.5 mol%, the molar fraction of the crosslinking agent RM82 is preferably 20 mol%, and the molar fraction of the photoinitiator 651 is preferably 1.5 mol%.

[0091] In practical applications, the molar fraction of liquid crystal polymer monomer RM006 can be 60-80 mol, the molar fraction of crosslinking agent RM82 can be 15-30 mol, and the molar fraction of photoinitiator 651 can be 1-5 mol, which can be adjusted according to actual needs.

[0092] After the liquid crystal elastomer prepolymer cools to room temperature, the second liquid crystal cell is subjected to ultraviolet (UV) exposure until the liquid crystal elastomer prepolymer polymerizes and solidifies. The temperature during UV exposure of the second liquid crystal cell is approximately 25°C to 30°C. The UV light intensity is preferably 4-6 mW / cm². 2 The exposure time is no less than 5 minutes. In this embodiment, the ultraviolet light intensity is preferably 5 mW / cm². 2 The preferred exposure time is 5 minutes.

[0093] The polymerized and cured liquid crystal elastomer prepolymer is peeled off from the second liquid crystal cell to obtain the target liquid crystal elastomer microstructure.

[0094] The liquid crystal elastomer microstructure film prepared by the method provided in this embodiment can have a thickness ranging from a few micrometers to tens of micrometers and exhibits good orientation. The orientation direction is determined by the orientation layers of the two substrates and directly affects the deformation state in response to thermal stimulation. The structural morphology of the liquid crystal elastomer microstructure can be arbitrarily designed based on a grayscale mask with precision down to the micrometer level. The resulting liquid crystal elastomer microstructure has high precision and can be used in high-precision equipment. Combined with liquid crystal cell fabrication processes, large-area, low-cost, and mass-producible liquid crystal elastomer microstructures can be fabricated.

[0095] Furthermore, since liquid crystals have the fluidity of liquids and are soluble in certain solvents, in another embodiment, a method is used to prepare liquid crystal elastomer microstructures by dissolving the liquid crystals with a solvent without damaging the polymer structure and alignment layer. Ethanol is preferred here, but not a limitation.

[0096] Figure 7 This is a flowchart illustrating one embodiment, such as... Figure 7As shown, in this embodiment, S4 is specifically implemented as follows:

[0097] S41' Clean the composite structure until all the liquid crystal in the composite structure is washed out.

[0098] Specifically, the composite structure with the grayscale mask removed can be immersed in an ethanol solution for 12 hours, and then dried after all the liquid crystal has been washed out.

[0099] In practical applications, the composite structure liquid crystal cell can also be disassembled, cleaned, and then reassembled into a cell.

[0100] S42'. The cleaned composite structure is filled with a pre-configured liquid crystal elastomer prepolymer to obtain a third liquid crystal cell; the third liquid crystal cell includes a first substrate, a second substrate and a liquid crystal elastomer prepolymer filled between the first substrate and the second substrate.

[0101] Specifically, during the filling process, the temperature of the liquid crystal elastomer prepolymer is preferably 90°C. S43' is then performed when the liquid crystal elastomer prepolymer temperature cools to room temperature.

[0102] S43', The first surface of the first substrate of the third liquid crystal cell is subjected to ultraviolet exposure until the liquid crystal elastomer prepolymer is polymerized and cured.

[0103] During ultraviolet exposure, the ultraviolet light intensity can be selected as 4-6 mW / cm². 2 The exposure time is no less than 5 minutes. In this embodiment, the ultraviolet light intensity is preferably 5 mW / cm². 2 The optimal exposure time is 5 minutes.

[0104] S44': The polymerized and cured liquid crystal elastomer prepolymer is peeled off from the second liquid crystal cell to obtain the liquid crystal elastomer microstructure.

[0105] In this embodiment, the upper and lower substrates in the first liquid crystal cell are two 2.5cm×2.5cm glass substrates that have been ultrasonically cleaned. One of them is hydrophilically treated and then spin-coated with polyimide (PI) as an alignment layer at a speed of 3000 rpm for 30 seconds. After baking at 200°C for 2 hours, it is rubbed to align after cooling to room temperature at a speed of 1000 rpm.

[0106] In this embodiment, the first liquid crystal cell is unidirectionally oriented, and the orientation direction of its orientation layer determines the orientation direction of the final liquid crystal elastomer. Due to the single-sided anchoring, the thickness that can achieve good orientation is limited.

[0107] Furthermore, such as Figure 2 and Figure 8As shown, one embodiment of the present invention also provides another method for preparing liquid crystal elastomer microstructures based on photopolymerization phase separation. Considering that the liquid crystal elastomer prepolymer also contains photopolymer monomers, which are the same as the polymer monomers in the aforementioned mixture of photopolymer monomers and liquid crystal, and can be used as a substitute, the filling layer filled in the liquid crystal cell is set as a liquid crystal mixture layer comprising the liquid crystal elastomer prepolymer and liquid crystal. The method includes:

[0108] A1. For a fourth liquid crystal cell of a specified thickness, a mixture of liquid crystal elastomer prepolymer and liquid crystal is filled between the fifth substrate and the sixth substrate of the fourth liquid crystal cell, and an alignment layer is coated on the second side of the fifth substrate and the first side of the sixth substrate; the fifth substrate is the upper substrate and the sixth substrate is the lower substrate; the second side of the fifth substrate and the first side of the sixth substrate both face the mixture.

[0109] Specifically, the second side of the fifth substrate and the first side of the sixth substrate are coated with an alignment layer. The alignment process involves ultrasonically cleaning the glass substrate, hydrophilic treatment, and then spin-coating a 1% PVA aqueous solution as the alignment layer at a speed of 3000 rpm for 30 seconds. After baking at 70°C for 40 minutes, the substrate is rubbed for alignment at a speed of 1000 rpm.

[0110] In one embodiment, the cell thickness of the fourth liquid crystal cell is controlled by microspheres of 15 μm.

[0111] A2. A grayscale mask is applied to the first surface of the fifth substrate of the fourth liquid crystal cell; the first surface of the fifth substrate is the surface away from the mixture.

[0112] A3. Expose the grayscale mask to ultraviolet light until the liquid crystal elastomer prepolymer and liquid crystal are completely separated, and the liquid crystal elastomer prepolymer is aggregated on the second side of the fifth substrate to form a liquid crystal elastomer microstructure, and the liquid crystal is aggregated on the first side of the sixth substrate.

[0113] In one embodiment, when the fourth liquid crystal cell undergoes ultraviolet exposure, the temperature of the liquid crystal elastomer prepolymer can be 65-75°C; the intensity of the ultraviolet light during ultraviolet exposure can be 0.4-0.8 mW / cm². 2 The exposure time can be 20-40 minutes. Specifically, the UV light intensity for the UV exposure is preferably 0.6 mW / cm². 2 The preferred exposure time is 30 minutes.

[0114] A4. Peel the liquid crystal elastomer microstructure from the fourth liquid crystal cell to obtain the liquid crystal elastomer microstructure.

[0115] In the mixture of liquid crystal elastomer prepolymer and liquid crystal, the mass ratio of liquid crystal elastomer prepolymer to liquid crystal is 1:1.

[0116] The liquid crystal polymer monomer RM006 in the liquid crystal elastomer prepolymer can have a molar fraction of 60-80 mol, the crosslinking agent RM82 can have a molar fraction of 15-30 mol, and the photoinitiator 651 can have a molar fraction of 1-5 mol, and is assembled according to actual needs.

[0117] This embodiment describes a double-sided oriented liquid crystal cell, exposed using only two glass substrates coated with alignment layers and a grayscale mask. During ultraviolet exposure, monomers in the liquid crystal elastomer prepolymer gradually polymerize, and the crosslinking agent gradually forms a crosslinked network, accumulating on the substrate near the light source and undergoing phase separation from the liquid crystal. After polymerization, a composite structure with phase separation of the liquid crystal elastomer and liquid crystal is obtained. This directly achieves phase separation of the liquid crystal elastomer and liquid crystal; after opening the cell and washing away the liquid crystal, a liquid crystal elastomer microstructure film is obtained. The structure is simple, the steps are streamlined, and the cost is low. Combined with the liquid crystal panel processing flow, it enables the preparation of large-area, low-cost, and mass-producible liquid crystal elastomer microstructures.

[0118] The present invention also provides a liquid crystal elastomer microstructure, which is prepared by the method described in any of the above embodiments.

[0119] The preset grayscale information of a grayscale mask directly affects the surface morphology of the resulting polymer. Different grayscale values ​​cause differences in light transmittance, which in turn affects the rate of photopolymerization at different locations, leading to the lateral diffusion and accumulation of polymer monomers, thus forming different polymer microstructures. By adjusting the preset grayscale information of the grayscale mask, various microstructure arrays such as lenses and gratings can be fabricated. In practical applications, the grayscale mask should be determined based on specific requirements and designed accordingly.

[0120] In one embodiment, a grayscale mask with grayscale information of a target cylindrical lens array, with a period of 200 μm, is used to fabricate the target cylindrical lens array. Optical inspection is then performed on the target cylindrical lens array, such as... Figure 4 As shown, Figure 4 These are multiple optical images of the target cylindrical lens array. The microstructure morphology can be characterized through these optical images. Figure 4 (a) is an optical microscopic image of a liquid crystal elastomer micropillar lens array; Figure 4 (b) is a polarization optical microscopy image of the liquid crystal elastomer micropillar lens array oriented at a 0° angle to the analyzer; Figure 4 (c) is a polarization optical microscopy image of the liquid crystal elastomer micropillar lens array oriented at a 45° angle to the analyzer; Figure 4 Image (d) shows the white light interference image and a schematic diagram of the cross-sectional sag of the liquid crystal elastomer micropillar lens array. Figure 4 It can be seen that the prepared liquid crystal elastomer microstructure has a good cylindrical lens array surface morphology and good orientation.

[0121] Liquid crystal elastomer microstructures have a fixed orientation, determined by the orientation layers of the two substrates, directly affecting the deformation state in response to thermal stimuli. Taking a single parallel orientation as an example, increasing temperature causes the liquid crystal elastomer microstructure array to shrink along the orientation direction and elongate perpendicular to it, thus altering its three-dimensional morphology and affecting optical properties and surface hydrophilicity / hydrophobicity. Taking a cylindrical lens array structure as an example, orientation along the cylindrical lens structure direction can achieve an optical response where the focal length increases with increasing temperature; orientation perpendicular to the structure direction can achieve an optical response where the focal length decreases with increasing temperature. Furthermore, by incorporating light-absorbing dyes or azobenzene into the liquid crystal elastomer prepolymer, photo-controlled microstructure devices can be realized based on photothermal or photochemical effects.

[0122] The liquid crystal elastomer microstructure array prepared by the method of the present invention can be used in thermally / optically tunable optical devices. Taking a cylindrical lens array as an example, different orientation directions can achieve bidirectional modulation of the lens focal length under temperature control.

[0123] like Figure 5 As shown, Figure 5 This is a schematic diagram illustrating the focusing effect of a liquid crystal elastomer micropillar lens array prepared in one embodiment at different temperatures. The incident light source is preferably a beam-expanded 532nm laser. Figure 5 (a) is a schematic diagram comparing the focusing effect of the liquid crystal elastomer micropillar lens array provided in one embodiment when the incident polarized light is parallel to the direction of the liquid crystal elastomer micropillar lens at 20°C and 260°C.

[0124] Figure 5 (b) is Figure 5 A schematic diagram comparing the focusing effect of the liquid crystal elastomer micropillar lens array provided in embodiment (a) with incident polarized light perpendicular to the direction of the liquid crystal elastomer micropillar lens at 20°C and 260°C. Figure 5 It can be seen that the prepared liquid crystal elastomer micropillar lens has a good focusing effect for incident light with a polarization direction parallel to the orientation direction, with a focal length of approximately 950 nm at room temperature; when the temperature is increased to 260℃, the focal length becomes 1450 nm. For incident light with a polarization direction perpendicular to the orientation direction, the focal length is approximately 1250 nm at room temperature; when the temperature is increased to 260℃, the focal length becomes 1600 nm.

[0125] The mechanism for adjustable focal length is that as the temperature increases, the liquid crystal molecules gradually change from an ordered nematic phase to a disordered isotropic state. Macroscopically, this manifests as the sample shrinking along the orientation direction, i.e., the direction of the cylindrical lens structure, and elongating perpendicular to the orientation direction. In this example, the cylindrical lens structure becomes wider and thicker, with the increase in width exceeding the increase in thickness. The surface of the cylindrical lens becomes smoother, and the focal length becomes longer.

[0126] In another embodiment, the grayscale mask is preset with grayscale information as a liquid crystal elastomer microlens array, with a lens period of 240 μm. The first liquid crystal cell used has a thickness of 25 μm, and the fabricated product is a liquid crystal elastomer microlens array. For example... Figure 6 As shown, see Figure 6 (a) is an optical microscopic image of the liquid crystal elastomer microlens array; Figure 6 (b) is a polarization optical microscopy image of the liquid crystal elastomer micro-lens array; Figure 6 (c) is a polarized optical microscopy image of the liquid crystal elastomer micro-lens array at a 45° angle; Figure 6 (d) is a white light interference image of the liquid crystal elastomer microstructure of the liquid crystal elastomer micro-circular lens array and a schematic diagram of its cross-sectional sagitta. Figure 6 (e) is an optical microscopic image of the liquid crystal elastomer microstructure of the liquid crystal elastomer micro circular lens array and a schematic diagram of the focusing effect in this region. Figure 6 (f) is a schematic diagram showing that the incident light polarization of the liquid crystal elastomer microstructure of the liquid crystal elastomer micro-circular lens array is parallel to the orientation direction. Figure 6 (g) is a schematic diagram of the incident light polarization perpendicular to the orientation direction of the liquid crystal elastomer microstructure of the liquid crystal elastomer microlens array.

[0127] Depend on Figure 6 As can be seen, the prepared liquid crystal elastomer microlens array has good orientation and a good microlens array morphology. It exhibits good focusing effect under conditions where the incident polarized light is parallel to and perpendicular to the orientation direction, with focal lengths of approximately 1600 μm and 2000 μm, respectively.

[0128] The present invention provides a method for fabricating liquid crystal elastomer microstructures based on photopolymerization phase separation. The method is simple and straightforward, achieving various surface morphologies such as lenses and gratings simply by adjusting the grayscale gradient and distribution of a grayscale mask. Furthermore, it can fabricate well-aligned liquid crystal elastomer microstructure arrays ranging from a few micrometers to tens of micrometers in thickness, with structural precision down to the micrometer level. This method effectively enables the fabrication of low-cost, high-precision, mass-producible, and large-area liquid crystal elastomer microstructures.

[0129] The liquid crystal elastomer microstructures prepared in the various embodiments provided by this invention have good orientation, and the prepared thickness can be between a few micrometers and tens of micrometers. The structural precision can reach the micrometer level. By adjusting the size of the liquid crystal cell, grayscale mask and ultraviolet exposure light source, large-area and multi-specification mass production is also possible, which has good application prospects.

[0130] In the description of this invention, it should be understood that "a plurality of" means two or more, unless otherwise explicitly specified.

[0131] In the description of this specification, the terms "one embodiment," "some embodiments," "embodiment," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0132] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make modifications, alterations, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for preparing liquid crystal elastomer microstructures based on photopolymerization phase separation, characterized in that, include: S1. For a first liquid crystal cell of a specified thickness, a mixture of photopolymer monomer and liquid crystal is filled between a first substrate and a second substrate of the first liquid crystal cell. The first substrate is an upper substrate without an alignment layer, the second substrate is a lower substrate, and an alignment layer is coated on the first surface of the second substrate facing the mixture. S2. A grayscale mask is applied to the first surface of the first substrate of the first liquid crystal cell; the first surface of the first substrate is the surface away from the mixture. S3. Expose the grayscale mask to ultraviolet light until the photopolymer monomers and liquid crystals are completely separated, and the photopolymer monomers are aggregated on the second side of the first substrate to form a polymer microstructure film, and the liquid crystals are aggregated on the first side of the second substrate to obtain a composite structure. S4. Based on the pre-configured liquid crystal elastomer prepolymer, the composite structure is processed according to the preset liquid crystal elastomer microstructure preparation strategy to obtain the liquid crystal elastomer microstructure. The S4 includes: S41. A first substrate in which a polymer microstructure film is aggregated in a composite structure is pretreated to obtain a third substrate, wherein the polymer microstructure film aggregated on the second side of the third substrate has an orientation layer. S42. A second liquid crystal cell is formed using a third substrate and a fourth substrate; a liquid crystal elastomer prepolymer is filled between the third substrate and the fourth substrate of the second liquid crystal cell; an alignment layer is provided on the first side of the fourth substrate facing the liquid crystal elastomer prepolymer, and the second side of the third substrate faces the liquid crystal elastomer prepolymer. S43. Expose the first surface of the third substrate of the second liquid crystal cell to ultraviolet light until the liquid crystal elastomer prepolymer is polymerized and cured; S44. The polymerized and cured liquid crystal elastomer prepolymer is peeled off from the second liquid crystal cell to obtain the liquid crystal elastomer microstructure.

2. The method for preparing liquid crystal elastomer microstructures as described in claim 1, characterized in that, S41 includes: S41-1. The first substrate in the composite structure is cleaned, dried and subjected to ultraviolet ozone hydrophilic treatment. S41-2. Spin-coat the first substrate after hydrophilic treatment with a polyvinyl alcohol aqueous solution and dry it. S41-3. The dried first substrate is rubbed to form an orientation layer on the surface of the polymer microstructure film on the first substrate, thus obtaining the third substrate.

3. The method for preparing liquid crystal elastomer microstructures as described in claim 1, characterized in that, The S4 includes: S41' Clean the composite structure until all the liquid crystal in the composite structure is washed out; S42' Fill the cleaned composite structure with a pre-configured liquid crystal elastomer prepolymer to obtain a third liquid crystal cell; the third liquid crystal cell includes a first substrate, a second substrate and a liquid crystal elastomer prepolymer filled between the first substrate and the second substrate; S43', The first surface of the first substrate of the third liquid crystal cell is exposed to ultraviolet light until the liquid crystal elastomer prepolymer is polymerized and cured; S44': The polymerized and cured liquid crystal elastomer prepolymer is peeled off from the second liquid crystal cell to obtain the liquid crystal elastomer microstructure.

4. The method for preparing liquid crystal elastomer microstructures as described in claim 1, characterized in that, The pre-configured liquid crystal elastomer prepolymer includes liquid crystal polymer monomers, crosslinking agents, and photoinitiators; The liquid crystal polymer monomer has a molar fraction of 60 mol%-80 mol%. The molar fraction of the crosslinking agent is 15 mol%-30 mol%. The molar fraction of the photoinitiator is 1 mol to 5 mol.

5. The method for preparing liquid crystal elastomer microstructures as described in claim 1, characterized in that, During the ultraviolet exposure of the grayscale mask in S3, the temperature of the mixture of photopolymer monomer and liquid crystal remains stable at 100±10℃.

6. The method for preparing liquid crystal elastomer microstructures as described in claim 5, characterized in that, The intensity of ultraviolet light used for ultraviolet exposure of the grayscale mask is 0.4-0.8 mW / cm². 2 The exposure time is 20-40 minutes.

7. A method for preparing liquid crystal elastomer microstructures based on photopolymerization phase separation, characterized in that, include: A1. For a fourth liquid crystal cell of a specified thickness, a mixture of liquid crystal elastomer prepolymer and liquid crystal is filled between the fifth and sixth substrates of the fourth liquid crystal cell, and an alignment layer is coated on the second side of the fifth substrate and the first side of the sixth substrate; the fifth substrate is the upper substrate and the sixth substrate is the lower substrate; the second side of the fifth substrate and the first side of the sixth substrate both face the mixture. A2. A grayscale mask is applied to the first surface of the fifth substrate of the fourth liquid crystal cell; the first surface of the fifth substrate is the surface away from the mixture. A3. Expose the grayscale mask to ultraviolet light until the liquid crystal elastomer prepolymer and liquid crystal are completely separated, and the liquid crystal elastomer prepolymer is aggregated on the second side of the fifth substrate to form a liquid crystal elastomer microstructure, and the liquid crystal is aggregated on the first side of the sixth substrate. A4. Peel the liquid crystal elastomer microstructure from the fourth liquid crystal cell to obtain the liquid crystal elastomer microstructure.

8. The method for preparing liquid crystal elastomer microstructures as described in claim 7, characterized in that, In the mixture of liquid crystal elastomer prepolymer and liquid crystal, the mass ratio of liquid crystal elastomer prepolymer to liquid crystal is 1:

1.

9. A liquid crystal elastomer microstructure, characterized in that, It is formed using the preparation method described in any one of claims 1 to 8.

Images