Single-domain liquid crystal elastomer, its preparation method and liquid crystal driving element

Abstract

The present invention provides a liquid crystal elastomer, a preparation method thereof, and a liquid crystal driving element. The liquid crystal elastomer is obtained by polymerizing a liquid crystal monomer, a chain extender, and a crosslinking agent. The liquid crystal monomer is selected from bis-end acrylate liquid crystal monomers. The chain extender is selected from dithiol monomers. The crosslinking agent is selected from one or more of trithiol monomers and tetrathiol monomers. The liquid crystal elastomer of the present invention can still further spontaneously elongate after being stretched at room temperature and fixing both ends. The liquid crystal elastomer after self-elongation can be further placed at room temperature to fix a single domain and obtain a single-domain liquid crystal elastomer.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid crystal materials, and particularly relates to a single-domain liquid crystal elastomer, a preparation method thereof, and a liquid crystal driving element. Background Art

[0002] Liquid crystal elastomers (LCEs) are a class of intelligent materials that possess both entropy elasticity and liquid crystallinity. LCEs can undergo reversible deformation under external stimuli, and thus can be used as driving devices, such as artificial muscles, valves in microfluidic systems, etc.

[0003] The prerequisite for LCEs to possess driving performance is to form single-domain liquid crystal elastomers. A single domain refers to the ordered arrangement of liquid crystal units within the crosslinked network to form a uniform orientation. Single-domain LCEs are in an anisotropic phase (liquid crystal phase) below the liquid crystal transition temperature (Ti), with the liquid crystal units being ordered, and in an isotropic phase above Ti, with the liquid crystal units being disordered. When subjected to external stimuli, the polymer chains undergo a phase change between the isotropic phase and the anisotropic phase, thereby undergoing reversible deformation. Currently, commonly used methods for fixing single domains include the two-step orientation method, the dynamic covalent bond method, etc. All of these methods invariably require external energy input, such as heating, ultraviolet light irradiation, solvent assistance, and external magnetic fields, etc. These methods have certain operational difficulties, relatively severe conditions, and require a large amount of energy consumption.

[0004] In addition, under unchanged external conditions, all currently known liquid crystal elastomers can only undergo elastic or plastic deformation after being stretched. Regardless of which type of deformation occurs, when they are stretched and the two ends are fixed, they can only maintain the current length and cannot further elongate without external stimuli. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a liquid crystal elastomer that can still further spontaneously elongate after being stretched and the two ends are fixed at room temperature, and this process does not require any change in external conditions or additional energy input. The liquid crystal elastomer after self-elongation can be further placed at room temperature to fix the single domain and obtain a single-domain liquid crystal elastomer.

[0006] The first aspect of the present invention provides a preparation method of a liquid crystal elastomer, which includes the following steps:

[0007] (a) Polymerize a liquid crystal monomer, a chain extender, and a crosslinking agent to obtain a liquid crystal elastomer, wherein the liquid crystal monomer is selected from the compound represented by formula (I), the chain extender is selected from dithiol monomers, and the crosslinking agent is selected from one or more of trithiol monomers and tetrathiol monomers,

[0008]

[0009] In formula (I), the R 1 、R2 , R 3 , R 4 Each independently represents hydrogen or methyl, and said R 5 and R 6 Each independently represents an alkylene group having 3 to 6 carbon atoms.

[0010] The second aspect of the present invention provides a liquid crystal elastomer, which is obtained by a polymerization reaction of a liquid crystal monomer, a chain extender, and a crosslinking agent. Among them, the liquid crystal monomer is selected from the compounds represented by formula (I), the chain extender is selected from dithiol monomers, and the crosslinking agent is selected from one or more of trithiol monomers and tetrathiol monomers.

[0011]

[0012] In formula (I), the R 1 , R 2 , R 3 , R 4 Each independently represents hydrogen or methyl, and said R 5 and R 6 Each independently represents an alkylene group having 3 to 6 carbon atoms.

[0013] The third aspect of the present invention provides a liquid crystal driving device, in which the liquid crystal elastomer according to the present invention is adopted.

[0014] The liquid crystal elastomer obtained by the polymerization reaction of the appropriate liquid crystal monomer, chain extender, and crosslinking agent according to the present invention can still further spontaneously elongate after being stretched and fixed at both ends at room temperature, and this process does not require any change in external conditions or additional energy input. The liquid crystal elastomer after self-elongation can be further placed under the same conditions to fix a single domain and obtain a single-domain liquid crystal elastomer. Moreover, the single-domain liquid crystal elastomer of the present invention has excellent stability. Therefore, by using the liquid crystal elastomer of the present invention, the liquid crystal driving element can have higher driving stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the drawings without creative efforts.

[0016] Figure 1 is a schematic diagram of the preparation process of a single-domain liquid crystal elastomer provided by an embodiment of the present invention.

[0017] Figure 2 is a test chart of the driving deformation rate of the single-domain liquid crystal elastomer of Example 1 of the present invention.

[0018] Figure 3 It is a schematic structural diagram of the liquid crystal elastomer of Embodiment 2 of the present invention. Detailed implementation manners

[0019] In order to make the invention object, technical solutions and beneficial technical effects of the present invention clearer, the present invention will be described in detail below in conjunction with specific embodiments. It should be understood that the embodiments described in this specification are only for explaining the present invention and not for limiting the present invention.

[0020] For simplicity, only some numerical ranges are explicitly disclosed herein. However, any lower limit can be combined with any upper limit to form a range not explicitly recited; and any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, although not explicitly recited, each point or single value between the range endpoints is included in the range. Thus, each point or single value can be used as its own lower or upper limit and combined with any other point or single value or combined with other lower or upper limits to form a range not explicitly recited.

[0021] In the description herein, it should be noted that unless otherwise specified, "above" and "below" include the recited number, and the meaning of "one or more" for "more than one" is more than two.

[0022] The above invention content of the present invention does not intend to describe every disclosed embodiment or every implementation manner of the present invention. The following description more specifically illustrates exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments, which can be used in various combinations. In each embodiment, the enumeration is only as a representative group and should not be construed as exhaustive.

[0023] The present invention provides a method for preparing a liquid crystal elastomer, and the method includes step (a) of obtaining a liquid crystal elastomer by subjecting a liquid crystal monomer, a chain extender and a crosslinking agent to a polymerization reaction.

[0024] In step (a), the liquid crystal monomer is selected from bis-end acrylate liquid crystal monomers. In some embodiments, both ends of the main chain of the bis-end acrylate liquid crystal monomer are acrylate groups. In some embodiments, preferably, the liquid crystal monomer is selected from the compounds represented by formula (I).

[0025]

[0026] In formula (I), R 1 , R 2 , R 3 , R 4 each independently represents hydrogen or methyl, R 5 and R 6Each independently represents an alkylene group having 3 to 6 carbon atoms.

[0027] In some embodiments, R 1 , R 2 , R 3 , R 4 One or more of them represent a methyl group. Optionally, one of R 1 , R 2 , R 3 , R 4 represents a methyl group, and the rest represent hydrogen. For example, R 1 represents a methyl group, and R 2 , R 3 and R 4 both represent hydrogen.

[0028] In any embodiment of the present invention, the alkylene group having 3 to 6 carbon atoms represents an alkylene group having 3 to 6 carbon atoms. Examples of the alkylene group having 3 to 6 carbon atoms may include n-propylene, isopropylidene, n-butylene, isobutylene, sec-butylene, tert-butylene, n-pentylene, isopentylene, n-hexylene, etc. One or several hydrogens in the alkylene group having 3 to 6 carbon atoms may be replaced by other elements or groups. Other elements may but are not limited to F, Cl, O, etc. Other groups may but are not limited to hydroxyl group, amino group, phenyl group, methoxy group, etc.

[0029] In some embodiments, R 5 and R 6 may each independently represent n-propylene, n-butylene, n-pentylene, or n-hexylene.

[0030] In some embodiments, the liquid crystal monomer may be selected from one or more of 1,4-bis[4-(3-acryloyloxypropoxy)-benzoyloxy]-2-methyl-benzene (RM257) and 1,4-bis[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methyl-benzene (RM82).

[0031]

[0032] In step (a), the chain extender is selected from dithiol monomers. In some embodiments, both ends of the main chain of the dithiol monomer are thiol groups. As an example, the chain extender may be selected from one or more of 2,2'-(1,2-ethylenedioxydioxy)bis(ethanethiol) (DODT), 3,6-dioxa-1,8-octanedithiol (EDDET), 1,3-propanedithiol, and 1,6-hexanedithiol.

[0033] In step (a), the crosslinking agent is selected from one or more of trithiol monomers and tetrathiols monomers. As an example, the crosslinking agent can be selected from one or more of 2-ethyl-2-[(3-mercapto-1-oxopropoxy)methyl]-1,3-propanediyl bis(3-mercaptopropionate) and pentaerythritol tetrakis(3-mercaptopropionate).

[0034] In some preferred embodiments, in step (a), the ratio of the total molar amount of acryloyloxy groups of the liquid crystal monomers to the total molar amount of mercapto groups of the chain extender and the crosslinking agent is 2:3 to 3:2. The total molar amount of acryloyloxy groups of the liquid crystal monomers refers to the total amount of acryloyloxy groups contained in all liquid crystal monomers in terms of moles. The total molar amount of mercapto groups of the chain extender and the crosslinking agent refers to the sum of the amount of mercapto groups contained in all chain extenders in terms of moles and the amount of mercapto groups contained in all crosslinking agents in terms of moles. When the ratio of the total molar amount of acryloyloxy groups of the liquid crystal monomers to the total molar amount of mercapto groups of the chain extender and the crosslinking agent is within an appropriate range, it is beneficial to make the reaction more complete and generate fewer impurities, thereby facilitating the obtaining of a monodomain liquid crystal elastomer with more excellent and stable driving performance. More preferably, the ratio of the total molar amount of acryloyloxy groups of the liquid crystal monomers to the total molar amount of mercapto groups of the chain extender and the crosslinking agent is 4:5 to 5:4, and further preferably 5:5 to 5:4.

[0035] In some preferred embodiments, in step (a), the molar ratio of the crosslinking agent to the chain extender is 1:2 to 1:20. When the molar ratio of the crosslinking agent to the chain extender is within an appropriate range, it is beneficial to make the reaction more complete and generate fewer impurities, thereby facilitating the obtaining of a monodomain liquid crystal elastomer with more excellent and stable driving performance. More preferably, the molar ratio of the crosslinking agent to the chain extender is 1:3 to 1:15, further preferably 1:3 to 1:12, further preferably 1:4 to 1:10, and even more preferably 1:6 to 1:10.

[0036] In some embodiments, in step (a), the liquid crystal monomers, the chain extender, and the crosslinking agent can undergo a polymerization reaction in a reaction solution. As an example, step (a) may include: (a1) providing a mixed solution containing the liquid crystal monomers, the chain extender, and the crosslinking agent; (a2) adding a catalyst to the mixed solution to catalyze the polymerization reaction of the liquid crystal monomers, the chain extender, and the crosslinking agent to generate a liquid crystal elastomer.

[0037] In step (a1), a liquid crystal monomer, a chain extender, and a crosslinking agent can be added to a solvent to form a mixed solution. The solvent can be an organic solvent. This organic solvent can dissolve the liquid crystal monomer, the chain extender, and the crosslinking agent. Preferably, this organic solvent is also easy to volatilize. For example, the boiling point of this organic solvent is below 120 °C, below 100 °C, below 80 °C, below 70 °C, or below 60 °C. In some embodiments, the boiling point of the organic solvent is 30 °C to 120 °C. In some embodiments, the boiling point of the organic solvent is 30 °C to 80 °C. In some embodiments, the boiling point of the organic solvent is 35 °C to 70 °C. As a specific example, the solvent can be selected from one or more of dichloromethane, tetrahydrofuran, and chloroform.

[0038] In some embodiments, preferably, in step (a1), the total mass percentage content of the liquid crystal monomer, the chain extender, and the crosslinking agent in the mixed solution is 20 wt% to 60 wt%, more preferably 30 wt% to 50 wt%. Keeping the total concentration of the liquid crystal monomer, the chain extender, and the crosslinking agent in the mixed solution within an appropriate range is beneficial for the single-domain liquid crystal elastomer obtained from the prepared liquid crystal elastomer to obtain higher driving performance.

[0039] In step (a2), the catalyst can be selected from the catalysts known in the art for catalyzing the polymerization reaction of acrylate liquid crystal monomers with mercapto chain extenders and mercapto crosslinking agents. For example, one or more of dipropylamine, triethylamine, and n-hexylamine. In some embodiments, based on the total mass of the liquid crystal monomer, the chain extender, and the crosslinking agent in the mixed solution, the usage amount of the catalyst is 0.1 wt% to 2 wt%, preferably 0.5 wt% to 1.5 wt%, such as 1 wt%.

[0040] Through the polymerization reaction in step (a2), the liquid crystal monomer is connected to the chain extender and the crosslinking agent to form a polymer. The temperature of the polymerization reaction can be selected as 20 °C to 30 °C, or 23 °C to 28 °C, such as 25 °C. The time of the polymerization reaction can be selected as 5 to 20 hours, or 10 to 15 hours, such as 12 hours.

[0041] In some embodiments, the polymerization reaction in step (a2) can be carried out in a mold so that the obtained liquid crystal elastomer can obtain the desired shape. The liquid crystal elastomer can be of any shape and can be selected according to actual needs. As an example, the liquid crystal elastomer can be in the shape of a thin film, a polyhedron (such as a cuboid, a cube, a cross shape, etc.), a cylinder, etc. Of course, the desired shape can also be obtained by subsequent processing such as cutting the liquid crystal elastomer.

[0042] The liquid crystal elastomer obtained by the present invention through the polymerization reaction of appropriate liquid crystal monomers, chain extenders and crosslinking agents can still further spontaneously elongate after being stretched at room temperature and fixing both ends, and this process does not require any change in external conditions or additional energy input. The liquid crystal elastomer after self-elongation can be further placed under the same conditions to fix a single domain and obtain a single-domain liquid crystal elastomer.

[0043] In some embodiments, the preparation method of the present invention further includes: (b) stretching the liquid crystal elastomer at 20°C to 30°C; (c) placing the stretched liquid crystal elastomer at 20°C to 30°C to enable the liquid crystal elastomer to undergo spontaneous elongation and fix the orientation, thereby obtaining a single-domain liquid crystal elastomer.

[0044] In some embodiments, the liquid crystal elastomer can be stretched at a deformation rate of 5% to 40%. Further optionally, the stretching deformation rate is 10% to 40%, 20% to 40%, or 25% to 35%, etc. The stretching deformation rate is the percentage of the increase in the size of the liquid crystal elastomer in the stretching direction to the original size of the liquid crystal elastomer in the stretching direction. The appropriate stretching deformation rate can be selected according to the reversible driving deformation rate of the desired single-domain liquid crystal elastomer. The larger the stretching deformation rate within an appropriate range, the correspondingly larger the reversible driving deformation rate of the single-domain liquid crystal elastomer.

[0045] In some embodiments, the stretching in step (b) can be uniaxial stretching or multi-directional stretching. If it is multi-directional stretching, the stretching deformation rate in each direction can be selected as 5% to 40%, 10% to 40%, 20% to 40%, or 25% to 35%, etc. Through multi-directional stretching, the driving performance in different direction orientations can be achieved on the same sample.

[0046] Step (b) can use methods known in the art to stretch the liquid crystal elastomer, such as applying a force along the stretching direction.

[0047] In some embodiments, preferably, the mass ratio of the solvent contained in the liquid crystal elastomer subjected to the stretching treatment in step (b) is 5% to 15%, and more preferably 5% to 8%. This mass ratio is the mass percentage of the solvent based on the total mass of the liquid crystal elastomer containing the solvent.

[0048] In some embodiments, after the polymerization reaction in step (a) and before the stretching in step (b), optionally, a step of pre-drying the liquid crystal elastomer is included. By pre-drying to remove the excessive solvent in the liquid crystal elastomer, the mass ratio of the solvent contained in the liquid crystal elastomer can be regulated within the desired range. Methods known in the art can be used to pre-dry the liquid crystal elastomer, such as vacuum drying. The drying temperature can be 20°C to 30°C.

[0049] In some embodiments, in step (c), the stretched liquid crystal elastomer can be placed at 20°C to 30°C. After observing the spontaneous elongation phenomenon, it can be further placed until the orientation of the liquid crystal elastomer is fixed, thus obtaining a single-domain liquid crystal elastomer. Spontaneous elongation means that the liquid crystal elastomer stretched in step (b) spontaneously elongates in length without any external stimulation.

[0050] In some embodiments, in step (c), the stretched liquid crystal elastomer can be placed at 20°C to 30°C for 10 to 16 hours to cause spontaneous elongation of the liquid crystal elastomer; then it can be further placed for 5 to 10 days to fix the orientation. Optionally, the placement temperature is 23°C to 28°C, such as 25°C. The time for the liquid crystal elastomer to be placed until spontaneous elongation occurs can be 10 to 16 hours, or 12 to 15 hours. The time for the liquid crystal elastomer to undergo spontaneous elongation to fixed orientation can be 5 to 10 days, or 6 to 8 days, such as 7 days.

[0051] In step (c), both ends in the stretching direction of the stretched liquid crystal elastomer can be fixed to keep its stretching deformation amount. Any method capable of fixing the deformation amount of the stretched liquid crystal elastomer can be used to fix its two ends, such as tape sticking or clamp clamping, etc.

[0052] Without wishing to be bound by any theory, the inventors believe that due to the isotropic state solution polymerization, the obtained liquid crystal elastomer is in a metastable state. After stretching, liquid crystal domains are gradually formed as the solvent volatilizes, thus spontaneously elongating. The elongated liquid crystal elastomer is in a stable state. The presence of a small amount of solvent reduces the activation energy of dynamic bond exchange, so that a single domain can ultimately be fixed. The single-domain liquid crystal elastomer obtained thereby has excellent stability, and does not require external energy input or external stimulation, and is simple and fast to prepare. The single-domain liquid crystal elastomer of the present invention can still maintain stable driving performance after 1000 thermal cycles in the temperature range of 20°C to 100°C.

[0053] The method for preparing the liquid crystal elastomer capable of spontaneous elongation at room temperature according to the present invention is simple, easy to operate, and highly practical, providing a new idea for preparing single-domain liquid crystal elastomers.

[0054] The present invention also provides a liquid crystal elastomer obtained according to the above preparation method.

[0055] The present invention also provides a liquid crystal driving device, in which the liquid crystal elastomer according to the present invention is adopted. The liquid crystal elastomer of the present invention can be applied to any field or device that requires a flexible driver, such as a blind display screen, a flexible robot, an artificial muscle, an artificial pupil, a bionic device, etc. In addition, the characteristic that the liquid crystal elastomer of the present invention can spontaneously elongate without external stimulation makes it have potential applications in the field of control systems without energy supply. Further, since the liquid crystal driving element adopts the liquid crystal elastomer of the present invention, it can have higher driving stability.

[0056] Example

[0057] The following examples more specifically describe the content disclosed by the present invention. These examples are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed by the present invention are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the examples are all commercially available.

[0058] In the following examples, an exemplary test method for the average driving deformation rate of the single-domain liquid crystal elastomer is as follows: Using a dynamic thermomechanical analyzer, the test temperature range is 20°C to 100°C, and it is cycled 1000 times. The driving deformation rate of each cycle = (the longest length at 20°C - the shortest length at 100°C) × 100% ÷ the shortest length at 100°C. The average value of 1000 cycles is recorded as the average driving deformation rate.

[0059] Example 1

[0060] At 25°C, 0.8 mmol of liquid crystal monomer RM257, 0.6 mmol of chain extender 2,2'-(1,2-ethylenedioxy)bis(ethanethiol), and 0.1 mmol of crosslinker pentaerythritol tetra(3-mercaptopropionate) were added to dichloromethane to obtain a mixed solution. The total mass fraction of the liquid crystal monomer, chain extender, and crosslinker in the mixed solution was 20 wt%. Based on the total mass of the liquid crystal monomer, chain extender, and crosslinker in the mixed solution, 1 wt% of the catalyst dipropylamine was added to the mixed solution. The mixed solution containing the catalyst was poured into a polytetrafluoroethylene mold and polymerized at 25°C for 12 hours. After the reaction, the polymer was demolded to obtain the liquid crystal elastomer.

[0061] Refer to Figure 1, the liquid crystal elastomer was cut into strips with a length of 15 mm, a width of 1.5 mm, and a thickness of 0.12 mm, uniaxially stretched along the length direction, and both ends were fixed, where the stretching deformation rate was 30%. The stretched liquid crystal elastomer was placed at 25 °C for 12 hours, and spontaneous elongation could be observed. After continuing to place for 7 days, a single domain could be fixed to obtain a single-domain liquid crystal elastomer.

[0062] From Figure 2 It can be seen that in this embodiment, the preparation method of the present invention is adopted, and the obtained single-domain liquid crystal elastomer has extremely high driving stability, and its average driving deformation rate is about 40%. Figure 2 Among them, the abscissa represents time (min), the left ordinate represents temperature (°C), and the right ordinate represents driving deformation rate (%).

[0063] Example 2

[0064] At 25 °C, 0.8 mmol of liquid crystal monomer RM257, 0.6 mmol of chain extender 2,2'-(1,2-ethylenedioxy) bis(ethyl mercaptan), and 0.1 mmol of crosslinker pentaerythritol tetra(3-mercaptopropionate) were added to dichloromethane to obtain a mixed solution. The total mass fraction of the liquid crystal monomer, chain extender, and crosslinker in the mixed solution was 20 wt%. Based on the total mass of the liquid crystal monomer, chain extender, and crosslinker in the mixed solution, 1 wt% of the catalyst dipropylamine was added to the mixed solution. The mixed solution containing the catalyst was poured into a polytetrafluoroethylene mold and polymerized at 25 °C for 12 hours. After the reaction, the polymer was demolded to obtain a liquid crystal elastomer.

[0065] The liquid crystal elastomer with a thickness of 0.15 mm was cut into a Figure 3 cross-shaped shape as shown, the four arms had equal dimensions, each arm had a length of 8 mm and a width of 1.2 mm. The four arms were simultaneously stretched and fixed along their respective length directions, where the stretching deformation rate of each arm was 30%. The stretched liquid crystal elastomer was placed at 25 °C for 12 hours, and spontaneous elongation of the four arms could be observed. After continuing to place for 7 days, a single domain could be fixed to obtain a single-domain liquid crystal elastomer.

[0066] In this embodiment, the preparation method of the present invention is adopted, and the obtained single-domain liquid crystal elastomer has extremely high driving stability in different orientations. In this cross-shaped single-domain liquid crystal elastomer, the average driving deformation rate of each arm is about 40%. This method realizes a flexible actuator with different orientation directions on the same sample, the preparation process is simple, and the success rate is high, providing a new idea for further preparing flexible actuators integrating multiple complex orientations.

[0067] Example 3

[0068] At 25 °C, 1.2 mmol of liquid crystal monomer RM257, 1.0 mmol of chain extender 2,2'-(1,2-ethylenedioxy)bis(ethanethiol), and 0.1 mmol of crosslinker pentaerythritol tetra(3-mercaptopropionate) were added to dichloromethane to obtain a mixed solution. The total mass fraction of the liquid crystal monomer, chain extender, and crosslinker in the mixed solution was 30 wt%. Based on the total mass of the liquid crystal monomer, chain extender, and crosslinker in the mixed solution, 1 wt% of the catalyst dipropylamine was added to the mixed solution. The mixed solution containing the catalyst was poured into a polytetrafluoroethylene mold and polymerized at 25 °C for 12 hours. After the reaction was completed, the polymer was demolded to obtain a liquid crystal elastomer.

[0069] The liquid crystal elastomer was cut into strips with a length of 15 mm, a width of 1.5 mm, and a thickness of 0.12 mm, uniaxially stretched along the length direction and the two ends were fixed, where the tensile deformation rate was 30%. The stretched liquid crystal elastomer was placed at 25 °C for 12 hours, and spontaneous elongation could be observed. After continuing to place it for 7 days, a single domain could be fixed to obtain a single-domain liquid crystal elastomer.

[0070] In this example, the preparation method of the present invention was adopted, and the obtained single-domain liquid crystal elastomer had extremely high driving stability, and its average driving deformation rate was about 48%.

[0071] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope determined by the claims.

Claims

1. A method for preparing a single-domain liquid crystal elastomer, characterized in that, Comprising the following steps: (a) Providing a mixed solution containing a liquid crystal monomer, a chain extender, and a crosslinking agent, wherein the total mass percentage content of the liquid crystal monomer, the chain extender, and the crosslinking agent in the mixed solution is 20 wt% to 60 wt%, and causing the liquid crystal monomer, the chain extender, and the crosslinking agent to undergo a polymerization reaction to obtain a liquid crystal elastomer, wherein the temperature of the polymerization reaction is 20°C to 30°C; (b) Stretching the liquid crystal elastomer at 20°C to 30°C with a deformation rate of 5% to 40%, wherein the deformation rate is the percentage of the increase in the size of the liquid crystal elastomer in the stretching direction to the original size of the liquid crystal elastomer in the stretching direction, and the mass ratio of the solvent contained in the stretched liquid crystal elastomer is 5% to 15%; (c) Placing the stretched liquid crystal elastomer at 20°C to 30°C for 10 to 16 hours to cause the liquid crystal elastomer to undergo spontaneous elongation, and the spontaneous elongation of the liquid crystal elastomer exceeds its deformation rate during stretching; then continuing to place it for 5 to 10 days to fix the orientation to obtain a single-domain liquid crystal elastomer; wherein, the liquid crystal monomer is selected from the compounds represented by formula (I), the chain extender is selected from dithiol monomers, and the crosslinking agent is selected from one or more of trithiol monomers and tetrathiol monomers, In formula (I), the R 1 , R 2 , R 3 , R 4 each independently represents hydrogen or methyl, and the R 5 and R 6 each independently represents an alkylene group having 3 to 6 carbon atoms.

2. The method according to claim 1, wherein The ratio of the total molar amount of acryloyloxy groups of the liquid crystal monomer to the total molar amount of mercapto groups of the chain extender and the crosslinking agent is 2:3 to 3:

2.

3. The method according to claim 1, characterized in that, The molar ratio of the crosslinking agent to the chain extender is 1:2 to 1:

20.

4. The method according to claim 1, wherein The liquid crystal monomer is selected from one or more of 1,4-bis[4-(3-acryloyloxypropoxy)-benzoyloxy]-2-methyl-benzene (RM257) and 1,4-bis[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methyl-benzene (RM82).

5. The method according to claim 1, characterized in that The chain extender is selected from one or more of 2,2'-(1,2-ethanediyldioxy)bis(ethanethiol) (DODT), 3,6-dioxa-1,8-octanedithiol (EDDET), 1,3-propanedithiol, and 1,6-hexanedithiol; and / or, The crosslinking agent is selected from one or more of 2-ethyl-2-[(3-mercapto-1-oxopropoxy)methyl]-1,3-propanediyl bis(3-mercaptopropionate) and pentaerythritol tetrakis(3-mercaptopropionate).

6. A single-domain liquid crystal elastomer prepared by the method according to any one of claims 1-5, wherein, The liquid crystal monomer is selected from the compounds represented by formula (I), the chain extender is selected from dithiol monomers, and the crosslinking agent is selected from one or more of trithiol monomers and tetrathiol monomers, In formula (I), the R 1 , R 2 , R 3 , R 4 each independently represents hydrogen or methyl, and the R 5 and R 6 each independently represents an alkylene group having 3 to 6 carbon atoms.

7. A liquid crystal driving device, wherein a single-domain liquid crystal elastomer obtained by the method according to any one of claims 1-5 or a single-domain liquid crystal elastomer according to claim 6 is used.

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