A reverse-driven liquid crystal elastomer and a method of making the same

Abstract

The application relates to the technical field of intelligent deforming polymer materials, and discloses a reverse-driven liquid crystal elastomer and a preparation method thereof. The preparation method comprises the following steps: (1) preparing a first heavy ordinary elastomer polymer; (2) swelling the first heavy ordinary elastomer polymer in a liquid crystal monomer precursor solution to obtain a gel material swollen with liquid crystal monomers; (3) applying external force to the gel material to program deformation, and simultaneously performing light irradiation to initiate polymerization to form a second heavy liquid crystal elastomer network, so that the reverse-driven liquid crystal elastomer is obtained. The liquid crystal elastomer base element is arranged along the direction perpendicular to the programmed external force, and macroscopic deformation is manifested as the material being elongated along the programmed external force direction when being heated and being contracted along the programmed external force direction when being cooled. The application provides a new method for orienting liquid crystal elastomers based on rebound force, the method has opposite driving characteristics compared with the reported liquid crystal elastomers oriented by mechanical force, and the method enriches the diversity of the deformation behavior of liquid crystal elastomers.

Description

Technical Field

[0001] This invention relates to the field of intelligent deformable polymer materials technology, and in particular to a reverse-driven liquid crystal elastomer and its preparation method. Technical Background

[0002] Liquid crystal elastomers (LCEs) are a class of intelligent polymer materials formed by the appropriate cross-linking of liquid crystal monomers, possessing both the orderliness of liquid crystals and the deformation properties of elastomers. This composite property allows LCEs to achieve precise and controllable reversible actuation under external stimuli, such as temperature, electric fields, or light fields, and they have broad application potential in fields such as soft robotics, artificial muscles, and biomedicine.

[0003] The key to achieving reversible actuation of liquid crystal elastomers (LCEs) is controlling the orientation of liquid crystal units within the polymer network to form single-domain liquid crystal elastomers. Existing orientation techniques include mechanical stretching, surface anchoring, and external field induction. Among these, mechanical stretching is currently the most widely used liquid crystal orientation method. An external force is applied to program the deformation of the prepared multi-domain liquid crystal elastomer, orienting the liquid crystal units along the programmed force direction. Fixing this orientation yields a single-domain liquid crystal elastomer. Reported mechanically stretched liquid crystal elastomers of this type all exhibit the same actuation mode: elongation along the programmed force direction upon cooling and contraction along the programmed force direction upon heating, resulting in a relatively simple actuation mode. Summary of the Invention

[0004] To address the limitations of existing alignment techniques and driving modes, the present invention aims to provide a reverse-driven liquid crystal elastomer and its preparation method. The liquid crystal elastomer units prepared by this invention are aligned perpendicular to the programmed external force direction, and the macroscopic deformation exhibits elongation along the programmed external force direction upon heating and contraction along the programmed external force direction upon cooling. This is the opposite of the driving behavior of mechanically stretched aligned liquid crystal elastomers, which exhibit cold elongation and thermal contraction.

[0005] The technical solution provided by this invention to achieve the above-mentioned technical objectives is as follows:

[0006] One objective of this invention is to provide a method for preparing a reverse-driven liquid crystal elastomer, comprising the following steps:

[0007] (1) Preparation of the first-order ordinary elastomer polymer;

[0008] (2) The first ordinary elastomer polymer obtained in step (1) is swollen in the liquid crystal monomer precursor liquid to obtain a gel material swollen with liquid crystal monomer.

[0009] (3) Apply external force to the gel material obtained in step (2) to program deformation, and simultaneously perform photo-induced polymerization to form a second liquid crystal elastomer network, thereby obtaining a reverse-driven liquid crystal elastomer.

[0010] In this invention, the first layer of ordinary elastomer polymer swells sufficiently in the liquid crystal monomer precursor solution. The swollen liquid crystal monomer precursor solution polymerizes under light irradiation, forming a second layer of liquid crystal elastomer network. After the external force is removed, a reverse-driven liquid crystal elastomer is obtained. After the external force is removed, the first layer of elastomer polymer tends to rebound. This rebound stress acts on the second layer of liquid crystal elastomer network, causing the liquid crystal cells to align perpendicular to the programmed external force direction. In contrast, the liquid crystal cells of liquid crystal elastomers oriented by conventional mechanical stretching methods are all oriented parallel to the programmed external force direction, thus exhibiting a driving mode opposite to the rebound force orientation method proposed in this invention.

[0011] Preferably, the first general-purpose elastomer polymer in step (1) is a thermosetting elastomer with good resilience, including one or more of polyurethane elastomers, polysiloxane elastomers, and polydiene rubbers. More preferably, the first general-purpose elastomer polymer is prepared by photocuring or thermocuring. More preferably, the polyurethane elastomer is a polyurethane containing acrylate-terminated groups, which can be polymerized by free radical initiation under a photoinitiator.

[0012] Preferably, the shape of the first ordinary elastomer polymer in step (1) is not limited; it can be a two-dimensional planar shape or a three-dimensional shape obtained by 3D printing or molding. More preferably, the shape of the first ordinary elastomer polymer can be obtained by photopolymerization 3D printing of polyurethane acrylate resin to obtain a complex three-dimensional shape.

[0013] Preferably, the liquid crystal monomer precursor solution in step (2) includes a liquid crystal monomer containing two-arm acrylate groups, a chain extender, and a photoinitiator.

[0014] More preferably, the liquid crystal monomer containing two-arm acrylate groups can be one or more of RM82, RM257, LC 756 and LC 242.

[0015] More preferably, the liquid crystal monomer content in the liquid crystal monomer precursor solution is 5%-80wt%.

[0016] More preferably, the chain extender is a chain extender monomer containing a two-arm thiol functional group or an amino functional group, more preferably 3,6-dioxa-1,8-octanedithiol or n-hexylamine.

[0017] More preferably, the reaction molar ratio of the liquid crystal monomer to the chain extender is not less than 1:1, and more preferably 1-2:1.

[0018] More preferably, the photoinitiator in the liquid crystal monomer precursor solution can be one or more of ultraviolet photoinitiators or visible photoinitiators, more preferably at least one of 2,2-dimethoxy-1,2-diphenylacetone (DMPA), phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (819) and diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and more preferably the photoinitiator is 0.05%-5 wt% of the total mass of liquid crystal monomer and chain extender.

[0019] Preferably, the liquid crystal monomer precursor solution in step (2) may further include a solvent, which may be one or more of toluene, chloroform, ethyl acetate, dimethylformamide and dimethyl sulfoxide.

[0020] Preferably, the swelling time in step (2) is not less than 30 min, more preferably 40 min to 3 h, so as to further ensure that the liquid crystal monomer can swell sufficiently.

[0021] Preferably, the external force used to program the deformation of the elastomeric gel material swollen with liquid crystal monomers in step (3) can be one or more of the following: stretching, rotation, compression, torsion, and bending.

[0022] More preferably, the external force for the programmed deformation can be combined with origami and paper-cutting structures to induce deformation.

[0023] Preferably, the light source in step (3) is at least one of ultraviolet light and visible light, and the illumination time is not less than 5s. More preferably, the illumination condition is 365nm ultraviolet light for 120s.

[0024] More preferably, step (3) may include a post-processing step after photopolymerization. When a solvent is present in the reaction system, the post-processing includes drying to remove the solvent.

[0025] Another object of the present invention is to provide a reverse-driven liquid crystal elastomer prepared by any of the above-described preparation methods.

[0026] Preferably, the macroscopic deformation of the liquid crystal elastomer is driven by temperature change, and the driving temperature is determined by the phase transition temperature of the liquid crystal elastomer.

[0027] More preferably, the temperature change may include one or more of direct heating drive, photothermal drive, and electrothermal drive.

[0028] Preferably, the liquid crystal elastomer units of the present invention are arranged along the direction perpendicular to the programmed external force. Under no external force, the macroscopic deformation is as follows: when heated above the liquid crystal phase transition temperature, the material elongates along the programmed external force direction; when cooled below the liquid crystal phase transition temperature, the material contracts along the programmed external force direction.

[0029] Preferably, the macroscopic deformation of the liquid crystal elastomer under external force depends on the relative magnitudes of the external force and the rebound internal stress. When the external force is greater than the internal stress, the material elongates when cooled and contracts when heated along the direction of the external force; when the external force is equal to the internal stress, the material does not undergo any driving force; when the external force is less than the internal stress, the material contracts when cooled and elongates when heated along the direction of the external force.

[0030] Preferably, the macroscopic deformation under the action of external force, combined with the geometric design of paper cutting or 3D printing, can control the relative magnitude of stress and external force in each region, thereby achieving multiple modes of driving cold extension and thermal contraction and cold contraction and thermal extension in the same material.

[0031] Compared with the prior art, the beneficial effects of the present invention are reflected in:

[0032] (1) The permanent shape preparation of the material in this invention is flexible and diverse. The synthesis and preparation of the first-stage ordinary elastomer polymer does not need to consider the orientation of the liquid crystal, and the polymerization molding method can be flexibly selected. The system can be either photocured or thermocured, and the molding method can be either molded or processed into various shapes by 3D printing.

[0033] (2) The driving modes of traditional mechanical stretching orientation liquid crystal elastomers are all cold extension and hot contraction along the programmed external force direction. In this invention, a new reverse driving mode of cold contraction and hot extension along the programmed external force direction is realized based on the spring-loaded internal stress orientation method.

[0034] (3) The present invention is based on a dual-network preparation method, which allows for diverse material system selection, simple orientation methods and preparation methods, and has a certain degree of universality.

[0035] (4) Based on the driving mode of cold contraction and thermal extension without external force in this invention, after applying an external force, the relative magnitude of stress and external force in each region can be controlled by combining the geometric design of paper cutting or 3D printing. Thus, multiple driving modes of cold extension and thermal contraction and cold contraction and thermal extension can be realized in the same material at the same time, which greatly enriches the diversity of liquid crystal elastomer deformation and has broad market application prospects. Attached Figure Description

[0036] Figure 1 This is a schematic diagram illustrating the process of preparing the reverse-driven liquid crystal elastomer in Example 1;

[0037] Figure 2 This is a schematic diagram illustrating the molecular network principle of the reverse-driven liquid crystal elastomer prepared in Example 1.

[0038] Figure 3 The strain curves of the reverse-driven liquid crystal elastomer prepared in Example 1 in a dynamic thermomechanical analyzer, and the WAXD two-dimensional diffraction pattern.

[0039] Figure 4 This is a schematic diagram of the deformation of the reverse-driven liquid crystal elastomer prepared in Example 1;

[0040] Figure 5 This is a schematic diagram comparing the deformation of the reverse-driven liquid crystal elastomer prepared in Example 2 and the conventional driven liquid crystal elastomer prepared in the comparative example.

[0041] Figure 6 This is a schematic diagram of the deformation of the 3D-printed reverse-driven liquid crystal elastomer in Example 3;

[0042] Figure 7 This is a schematic diagram of the deformation of the liquid crystal elastomer driven by multiple modes under the action of external force in Example 4. Detailed Implementation

[0043] The technical solution of the present invention will be further clearly and completely described below through specific embodiments and in conjunction with the accompanying drawings, so as to fully understand the purpose, solution and effect of the present invention. It should be understood that the embodiments described in the present invention are implemented under the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given, but they are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0044] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used in the examples are commercially available unless otherwise specified.

[0045] Example 1:

[0046] Raw materials: polyurethane acrylate EBCERYL 8413, 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (RM82), 3,6-dioxa-1,8-octanedithiol (EDDT), 2,2-dimethoxy-1,2-diphenylacetone (DMPA), and toluene.

[0047] The preparation method consists of the following steps:

[0048] Step 1) First, synthesize the polyurethane acrylate 8413 elastomer film material according to the following dosage ratio: Weigh 1g of 8413 and place it in a culture bottle, add 1g of toluene and 0.5wt% DMPA, and stir at 60℃ to dissolve into a clear liquid. Pour the solution into a silicone mold with glass as a clamp, and irradiate it under a UV lamp for 180s to obtain a polyurethane gel. Place it in a vacuum oven at 70℃ and dry for 12 hours to evaporate the solvent, obtaining a polyurethane film.

[0049] Step 2) Weigh 1g of RM82 and 0.27g of EDDT, add 3.73g of toluene and 0.5wt% DMPA, heat and stir at 60℃ to dissolve, and obtain a 20wt% concentration RM82 liquid crystal monomer precursor solution. Swell the prepared polyurethane film in this precursor solution for about 40 minutes to reach swelling equilibrium, and obtain a polyurethane gel swollen with liquid crystal monomers.

[0050] Step 3) The polyurethane gel is uniaxially stretched to 100% strain using a tensile jig, and then cured under ultraviolet light for 120 seconds to obtain a liquid crystal elastomer gel. The external force is removed, and the liquid crystal elastomer gel is dried in a vacuum oven at 70°C for 12 hours to obtain a reverse-driven liquid crystal elastomer.

[0051] Figure 1 This is a schematic diagram illustrating the process of preparing the reverse-driven liquid crystal elastomer in Example 1.

[0052] Figure 2 This is a schematic diagram illustrating the molecular network principle of the reverse-driven liquid crystal elastomer prepared in Example 1. The polyurethane elastomer film obtained in step 1 corresponds to... Figure 2 The molecular network I in step 2 corresponds to the polyurethane gel containing liquid crystal monomers obtained in step 2. Figure 2 The molecular network II in step 3 corresponds to the liquid crystal elastomer gel obtained after applying external force and photocuring. Figure 2 The molecular network III in the middle, the reverse-driven liquid crystal elastomer obtained after solvent evaporation corresponds to Figure 2 The molecular network IV in the polyurethane elastomer. Under the action of the rebound internal stress of the polyurethane elastomer, the liquid crystal units are oriented and aligned along the direction perpendicular to the programmed external force.

[0053] Figure 3 The strain curves and WAXD two-dimensional diffraction patterns of the reverse-driven liquid crystal elastomer prepared in Example 1 are shown in the dynamic thermomechanical analyzer. The WAXD two-dimensional diffraction pattern shows that the liquid crystal cells are oriented perpendicular to the direction of the programmed external force. Therefore, the strain curves show that the strain increases with increasing temperature and decreases with decreasing temperature.

[0054] Figure 4 This is a schematic diagram illustrating the deformation of the reverse-driven liquid crystal elastomer prepared in Example 1. When the temperature is raised above the liquid crystal phase transition temperature, such as 160°C, the sample elongates along the programmed direction of the external force; when the temperature is lowered below the phase transition temperature, such as 25°C, the sample contracts along the programmed direction of the external force. Through repeated heating and cooling, reversible driving of the sample's thermal elongation and cold contraction can be achieved.

[0055] Example 2:

[0056] The raw materials are the same as in Example 1.

[0057] The preparation method consists of the following steps:

[0058] Step 1) The polyurethane film is prepared using the same method as in Example 1. The polyurethane film is then further cut into flower-shaped pieces using a laser cutter.

[0059] Step 2) The preparation method of the liquid crystal monomer precursor solution is the same as in Example 1. The polyurethane film of the flower is swollen in the liquid crystal monomer precursor solution for about 40 minutes to reach swelling equilibrium, and a polyurethane gel with a flower appearance shape and swollen liquid crystal monomer is obtained.

[0060] Step 3) Apply external force to the polyurethane gel of the flower to bend its petals, and place it under ultraviolet light for 120 seconds to cure, thus obtaining the liquid crystal elastomer gel of the flower. Remove the external force and place the liquid crystal elastomer gel in a vacuum oven at 70°C for 12 hours to dry, thus obtaining the reverse-driven liquid crystal elastomer.

[0061] Comparative Example: Weigh 1g of RM82 and 0.27g of EDDT, add 3.73g of toluene and 0.5wt% DMPA, heat and stir at 60℃ to dissolve, obtaining a 20wt% concentration RM82 liquid crystal monomer precursor solution. Pour the precursor solution into a silicone mold with glass as a clamp, irradiate under a UV lamp for 120s to obtain a liquid crystal elastomer gel, and further cut the gel into a flower shape using a flower cutter. Apply external force to the flower liquid crystal elastomer gel to bend its petals, and dry it in a vacuum oven at 70℃ for 12 hours while maintaining the bent shape, to obtain a conventionally driven liquid crystal elastomer.

[0062] Figure 5 This diagram illustrates a deformation comparison between the reverse-driven liquid crystal elastomer prepared in Example 2 and the conventionally driven liquid crystal elastomer prepared in the comparative example. For the reverse-driven liquid crystal elastomer of this example, heating to above the liquid crystal phase transition temperature, such as 160°C, causes the petals to close; cooling to below the phase transition temperature, such as 25°C, causes the petals to open. Through repeated heating and cooling, reversible thermal elongation and cold contraction can be achieved; that is, heating causes deformation in the programmed direction, and cooling causes deformation in the opposite direction. For the conventionally driven liquid crystal elastomer of the comparative example, heating to 160°C causes the petals to open, and cooling to 25°C causes the petals to close. Through repeated heating and cooling, conventional thermal contraction and cold elongation are achieved; that is, cooling causes deformation in the programmed direction, and heating causes deformation in the opposite direction.

[0063] Example 3:

[0064] Raw materials: Polyurethane acrylate EBCERYL 8413, 1,4-bis-[4-(6-acryloyloxyhexyloxy)benzoyloxy]-2-methylbenzene (RM82), 3,6-dioxa-1,8-octanedithiol (EDDT), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (819), 2,2-dimethoxy-1,2-diphenyl ethyl ketone (DMPA), Sudan III, and toluene.

[0065] The preparation method consists of the following steps:

[0066] Step 1) Weigh 30g of 8413 and place it in a beaker. Add 30g of toluene, 0.5wt% of 819, and 0.5‰ of Sudan III. Stir at 60℃ to dissolve into a clear red liquid, thus obtaining the 3D printing photosensitive resin. Use a photopolymer 3D printer to print layer by layer into the designed Eiffel Tower or octopus shape. Place the polyurethane gel with the complex three-dimensional shape in a 70℃ vacuum oven for 24 hours to evaporate the solvent, obtaining the 3D printed polyurethane elastomer with the complex three-dimensional shape.

[0067] Step 2) The preparation method of the liquid crystal monomer precursor solution is the same as in Example 1. The polyurethane elastomer with a complex three-dimensional shape is swollen in the liquid crystal monomer precursor solution for about 1 hour to reach swelling equilibrium, resulting in a polyurethane gel with the shape of the Eiffel Tower or octopus swollen with liquid crystal monomers.

[0068] Step 3) Apply external force to the Eiffel Tower polyurethane gel to bend its top, and apply external force to the octopus polyurethane gel to flatten its legs. Curing is then performed under ultraviolet light for 120 seconds, yielding Eiffel Tower and octopus liquid crystal elastomer gels respectively. The external force is removed, and the liquid crystal elastomer gels are dried in a 70℃ vacuum oven for 24 hours to obtain a 3D-printed reverse-driven liquid crystal elastomer.

[0069] Figure 6 This is a schematic diagram illustrating the deformation of the 3D-printed reverse-drive liquid crystal elastomer in Example 3. For the Eiffel Tower liquid crystal elastomer, heating to 160°C causes the top to bend, while cooling to 25°C causes it to straighten. For the octopus liquid crystal elastomer, heating to 160°C causes the octopus legs to flatten, while cooling to 25°C causes them to retract. Through repeated heating and cooling, reversible extension and contraction due to heat can be achieved.

[0070] Example 4:

[0071] The raw materials and preparation steps 1, 2, and 3 are the same as in Example 1.

[0072] Step 4) Use a laser cutter to cut the obtained thin-film liquid crystal elastomer into the designed pattern. It is divided into three sections: the first section has the highest cutout density, the second section has a medium cutout density, and the third section is not cut. A 20g weight is hung along the programmed external force direction as a constant external force, thus obtaining a liquid crystal elastomer driven by multiple modes.

[0073] Figure 7 This is a schematic diagram illustrating the deformation of the liquid crystal elastomer under various modes of external force in Example 4. Under the same external force, the first segment exhibits normal cold elongation and thermal contraction deformation behavior because it has the highest perforation density, resulting in an external force per unit area greater than the rebound internal stress. The liquid crystal cells are oriented along the direction of the external force. The second segment exhibits normal cold elongation and thermal contraction deformation behavior because it has a medium perforation density, resulting in an external force per unit area almost equal to the rebound internal stress. The liquid crystal cells are not oriented, so the second segment does not exhibit any driven deformation behavior. The third segment exhibits reverse cold contraction and thermal elongation deformation behavior because it has no perforations, resulting in an external force per unit area less than the rebound internal stress. The liquid crystal cells are oriented along the direction perpendicular to the programmed external force.

[0074] Example 5:

[0075] Raw material: polydimethylsiloxane SYLGARD TM 184, 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM257), 3,6-dioxa-1,8-octanedithiol (EDDT), diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) and dimethylformamide.

[0076] Step 1) Weigh out SYLGARD TM 184 (precursor liquid: crosslinking agent mass ratio 10:1) was added to the culture bottle and stirred until homogeneous, then defoamed in a vacuum oven. The above precursor liquid was poured into an aluminum tray and heat-cured in an 80℃ oven for 2 hours to obtain polysiloxane elastomer.

[0077] Step 2) Weigh 1g of RM257 and 0.155g of EDDT, add 18.85g of dimethylformamide and 5wt% TPO, heat and stir at 60℃ to dissolve, and obtain a 5wt% concentration of RM257 liquid crystal monomer precursor solution. Swell the prepared polysiloxane elastomer in this precursor solution for about 2 hours to reach swelling equilibrium, and obtain a polysiloxane gel swollen with liquid crystal monomers.

[0078] Step 3) Twist the polysiloxane gel into a spiral using a stretching fixture and cure it under ultraviolet light for 120 seconds to obtain a liquid crystal elastomer gel. Remove the external force and dry the liquid crystal elastomer gel in a vacuum oven at 70°C for 24 hours to obtain a reverse-driven spiral liquid crystal elastomer. For this spiral liquid crystal elastomer, the number of spirals increases when the temperature is raised to 120°C, and decreases when the temperature is lowered to 25°C. By repeatedly raising and lowering the temperature, reversible driving of thermal elongation and cold contraction can be achieved.

[0079] Example 6:

[0080] Raw materials: Styrene-butadiene rubber, dicumyl peroxide, 2-methyl-1,4-phenylenebis(4-(((4-(acryloyloxy)butoxy)carbonyl)oxy)benzoate (LC242), n-hexylamine, 2,2-dimethoxy-1,2-diphenyl ethyl ketone (DMPA) and dimethyl sulfoxide.

[0081] Step 1) Mix 10g of styrene-butadiene rubber and 0.05g of dicumyl peroxide on a two-roll mill, and then hot press at 170°C in a hot press to obtain cross-linked polydiolefin rubber.

[0082] Step 2) Weigh 1g of LC242 and 0.096g of n-hexylamine, add 0.57g of dimethyl sulfoxide and 0.05wt% DMPA, heat and stir at 60℃ to dissolve, and obtain a 60wt% concentration LC242 liquid crystal monomer precursor solution. Swell the prepared polydiolefin rubber in this precursor solution for about 3 hours to reach swelling equilibrium, and obtain a polydiolefin gel swollen with liquid crystal monomers.

[0083] Step 3) The polydiene gel is uniaxially stretched to a strain of 200% using a stretching fixture. It is first reacted in an 80°C oven for 2 hours, then cured under UV light for 120 seconds to obtain a liquid crystal elastomer gel. The external force is removed, and the liquid crystal elastomer gel is dried in a 70°C vacuum oven for 24 hours to obtain a reverse-driven liquid crystal elastomer. For this liquid crystal elastomer, heating to 140°C causes the sample to elongate, and cooling to 25°C causes it to shorten. Through repeated heating and cooling, reversible thermal elongation and cold contraction can be achieved.

[0084] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications may be made without departing from the technical solutions described in the claims.

Claims

1. A reverse-driven liquid crystal elastomer, characterized in that, The liquid crystal elastomer units are arranged perpendicular to the programmed external force direction. Under no external force, their macroscopic deformation is characterized by elongation along the programmed external force direction upon heating and contraction along the programmed external force direction upon cooling. The preparation method of the liquid crystal elastomer includes the following steps: (1): Preparation of a first-stage common elastomer polymer; the first-stage common elastomer polymer in step (1) includes one or more of polyurethane elastomer, polysiloxane elastomer and polydiolefin rubber; (2): The first ordinary elastomer polymer is swollen in the liquid crystal monomer precursor solution to obtain a gel material swollen with liquid crystal monomer; the liquid crystal monomer precursor solution in step (2) includes liquid crystal monomer containing two-arm acrylate groups, chain extender and photoinitiator; (3): Apply external force to the gel material to program deformation, and simultaneously perform photo-induced polymerization to form a second liquid crystal elastomer network, thereby obtaining a reverse-driven liquid crystal elastomer.

2. A method for preparing a reverse-driven liquid crystal elastomer as described in claim 1, characterized in that, Includes the following steps: (1): Preparation of a first-stage common elastomer polymer; the first-stage common elastomer polymer in step (1) includes one or more of polyurethane elastomer, polysiloxane elastomer and polydiolefin rubber; (2): The first ordinary elastomer polymer is swollen in the liquid crystal monomer precursor solution to obtain a gel material swollen with liquid crystal monomer; the liquid crystal monomer precursor solution in step (2) includes liquid crystal monomer containing two-arm acrylate groups, chain extender and photoinitiator; (3): Apply external force to the gel material to program deformation, and simultaneously perform photo-induced polymerization to form a second liquid crystal elastomer network, thereby obtaining a reverse-driven liquid crystal elastomer.

3. The method for preparing a reverse-driven liquid crystal elastomer according to claim 2, characterized in that, The liquid crystal monomer containing two-arm acrylate groups can be one or more of RM82, RM257, LC 756 and LC 242.

4. The method for preparing a reverse-driven liquid crystal elastomer according to claim 2, characterized in that, The liquid crystal monomer precursor solution contains 5%-80wt% liquid crystal monomers.

5. The method for preparing a reverse-driven liquid crystal elastomer according to claim 2, characterized in that, The chain extender is a chain extender monomer containing a two-arm thiol functional group or an amino functional group, and the molar ratio of liquid crystal monomer to chain extender is not less than 1:

1.

6. The method for preparing a reverse-driven liquid crystal elastomer according to claim 2, characterized in that, The photoinitiator in the liquid crystal monomer precursor solution is one or more of ultraviolet photoinitiators and visible photoinitiators, and the photoinitiator accounts for 0.05%-5 wt% of the total mass of the liquid crystal monomer and chain extender.

7. The method for preparing a reverse-driven liquid crystal elastomer according to claim 2, characterized in that, The liquid crystal monomer precursor solution in step (2) also includes a solvent, which is one or more of toluene, chloroform, ethyl acetate, dimethylformamide and dimethyl sulfoxide.

8. The method for preparing a reverse-driven liquid crystal elastomer according to claim 2, characterized in that, In step (3), the external force that programs the deformation of the elastomeric gel material swollen with liquid crystal monomers is one or more of the following: stretching, rotation, compression, torsion, and bending.

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