Liquid crystal elastomers, their preparation methods and applications

Abstract

This invention provides a liquid crystal elastomer, its preparation method, and its applications. The liquid crystal elastomer comprises a liquid crystal polymer matrix and an MXene / nanocellulose / polydopamine composite material dispersed therein. The preparation method involves mixing the MXene / nanocellulose / polydopamine composite material with a liquid crystal elastomer precursor, followed by a Michael addition reaction to form a liquid crystal oligomer. The liquid crystal oligomer is then thermosetting, stretched, oriented, and subsequently polymerized under ultraviolet light to obtain the liquid crystal elastomer. The preparation method is simple and easy to control, and the resulting elastomer exhibits excellent light-driven and mechanical properties, making it suitable for applications such as light-driven actuators, soft robots, and artificial muscles, particularly in underwater applications.

Description

Technical Field

[0001] This invention relates to the field of biopolymer materials technology, and in particular to a liquid crystal elastomer, its preparation method, and its application. Background Technology

[0002] In nature, the stress responses of organisms to external stimuli have provided many new ideas for biomimetic researchers. Examples include chameleons and phototactic sunflowers. Materials that exhibit responsive changes in response to external stimuli such as light, temperature, and pH have been extensively studied. Currently, materials used in stimulus-responsive devices include liquid crystal elastomers, hydrogels, and shape memory polymers. Because these materials undergo macroscopic changes (such as size, shape, and surface morphology) upon stimulation, they are often used in soft actuators, sensors, and biological materials. Among them, liquid crystal elastomers, as a type of liquid crystal polymer, retain the anisotropy of liquid crystals while also possessing the elasticity of rubber. They can undergo reversible thermo-induced deformation by controlling temperature. Using the photothermal conversion effect to drive liquid crystal elastomers wirelessly, non-contactly, and remotely gives them the ability to adapt to various complex scenarios, making light-driven liquid crystal elastomers an excellent responsive material. However, liquid crystal elastomers are polymeric materials derived from liquid crystal monomers with slight cross-linking, and their insufficient mechanical properties limit their application in actuators and artificial muscles. Summary of the Invention

[0003] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a liquid crystal elastomer that possesses both good photoresponse and driving performance, as well as good mechanical properties, making it applicable in various environments. Furthermore, this invention also provides a method for preparing this liquid crystal elastomer and its applications.

[0004] Specifically, the present invention adopts the following technical solution:

[0005] A first aspect of the present invention is to provide a liquid crystal elastomer comprising a liquid crystal polymer matrix and an MXene / nanocellulose / polydopamine composite material dispersed therein; the liquid crystal polymer matrix is ​​formed by chemical bonds or crosslinking between liquid crystal polymer molecular chains; the MXene / nanocellulose / polydopamine composite material comprises MXene, nanocellulose and polydopamine coated on the MXene and nanocellulose.

[0006] The liquid crystal elastomer of the present invention is composed of a liquid crystal polymer filled with an MXene / nanocellulose / polydopamine composite material. The liquid crystal polymer, MXene, nanocellulose, and polydopamine interact through chemical crosslinking, entanglement, and physical interaction. The polymer molecular chains are connected or crosslinked by chemical bonds, MXene is crosslinked with each other by hydrogen bonds, MXene and nanocellulose are connected by van der Waals forces, and MXene and nanocellulose are crosslinked with polydopamine through the oxidative self-polymerization reaction of polydopamine. In addition, MXene and dopamine also have coordination bonds. The MXene, nanocellulose, polydopamine, and polymer molecular chains are also physically entangled and interact closely, which can improve the mechanical properties of the material.

[0007] Furthermore, MXene, as a novel two-dimensional material, exhibits a strong photothermal conversion effect due to its surface plasmon resonance, particularly in the near-infrared region. Using MXene as a photothermal dopant can drive the photo-stimulation of liquid crystal elastomers. In addition, MXene possesses strong intrinsic mechanical properties, and its addition can enhance the mechanical properties of liquid crystal elasticity. Nanocellulose, a biopolymer extracted from nature, can be used as a dispersant. Because nanocellulose and MXene exhibit both electrostatic repulsion and van der Waals forces, a micro-spacing exists between them, providing space for polydopamine to bind with MXene. This avoids direct cross-linking between MXene materials caused by the oxidative self-polymerization of dopamine, increasing the water dispersibility of the modified MXene. Simultaneously, nanocellulose also enhances mechanical properties, improving the mechanical properties of liquid crystals. Dopamine monomers can undergo oxidative self-polymerization in an aqueous environment with a pH of 8-9. The continuously formed polydopamine nanoparticles can form a film that encapsulates the surface of MXene and nanocellulose, reducing physical contact with water and occupying interaction sites between MXene and water, thereby slowing down the oxidation of MXene in aquatic environments or humid air. Simultaneously, polydopamine also possesses photothermal conversion properties, forming a synergistic photothermal conversion effect with MXene. Furthermore, the catechin groups on polydopamine have a certain hydrophobic effect, which can increase the dispersibility of the MXene / nanocellulose / polydopamine composite material within the liquid crystal polymer. Therefore, the liquid crystal elastomer of this invention has excellent photothermal response and mechanical properties, and has the potential to become an artificial muscle or actuator.

[0008] In some embodiments of the present invention, the amount of the MXene / nanocellulose / polydopamine composite material added to the liquid crystal elastomer is 0.1 to 1 wt%.

[0009] In some embodiments of the present invention, the liquid crystal polymer includes at least one of a low degree of polymerization liquid crystal oligomer, a low degree of crosslinking liquid crystal elastomer, and a high degree of crosslinking liquid crystal network.

[0010] In some embodiments of the present invention, the liquid crystal polymer includes at least one of a polyacrylate liquid crystal polymer, a liquid crystal polymer copolymerized from monoacrylate and diacrylate liquid crystals, and a liquid crystal polymer copolymerized from acrylate and thiol.

[0011] In some embodiments of the present invention, the mass ratio of MXene to nanocellulose is 1:4.5 to 10, the polydopamine is obtained by oxidative self-polymerization of dopamine monomer, and the mass ratio of dopamine monomer to MXene is 1:0.05 to 0.2, preferably 1:0.05 to 0.15, and more preferably 1:0.08 to 0.1.

[0012] In some embodiments of the present invention, the MXene / nanocellulose / polydopamine composite material is a complex formed by polydopamine on the surfaces of MXene and nanocellulose through its adhesive properties or chemical bonding. The catechin groups in polydopamine not only have adhesive properties but can also form hydrogen bonds and titanium coordination bonds with the MXene material, thus enabling it to adhere well to the MXene surface.

[0013] In some embodiments of the present invention, the chemical formula of the MXene includes M n+1 X n M is a transition metal, including at least one of Sc, Ti, Zr, Hf, V, Nb, Ta, Cr, and Mo; X is C or N; and n is an integer from 1 to 3. Preferably, M includes at least one of Ti, V, Nb, and V. More preferably, MXene includes at least one of Ti3C2, Ti2C, and Cr2C.

[0014] In some embodiments of the present invention, the M n+1 X n Obtained by acid etching of MAX material, wherein the chemical formula of MAX material is M n+1 AX n Where A is Al or Si. The acid includes at least one of hydrofluoric acid, concentrated hydrochloric acid, and a mixture of concentrated hydrochloric acid / fluoride salts. MAX material is a three-layer structure material that, after etching, forms M with a two-dimensional monolayer sheet structure. n+1 X n To streamline the process, the M... n+1 X nAlternatively, commercially available M can be used directly. n+1 X n .

[0015] In some embodiments of the present invention, the MXene / nanocellulose / polydopamine composite material contains at least one of cellulose nanocrystals (CNC), cellulose nanofibers (CNF), and bacterial cellulose (BC), preferably cellulose nanocrystals (CNC). In some examples of the present invention, the nanocellulose has a diameter of 5 nm to 20 nm and a length of 100 nm to 200 nm, and the mass ratio of MXene to nanocellulose is 1:4.5 to 10, preferably 1:4.5 to 7, and more preferably 1:4.5 to 5.5.

[0016] A second aspect of the present invention is to provide a method for preparing the above-mentioned liquid crystal elastomer, comprising the following steps:

[0017] S1 prepares MXene / nanocellulose / polydopamine composite materials;

[0018] S2 is used to prepare liquid crystal elastomers;

[0019] The MXene / nanocellulose / polydopamine composite material is mixed with an elastomer precursor, and a Michael addition reaction is carried out to form a liquid crystal oligomer. The elastomer precursor includes liquid crystal monomers and thiols.

[0020] The liquid crystal oligomer is thermosetting, stretched and oriented, and then polymerized under ultraviolet light to obtain the liquid crystal elastomer.

[0021] In some embodiments of the present invention, in step S1, a polydopamine layer formed after dopamine undergoes oxidative self-polymerization is coated onto the surface of MXene and nanocellulose to obtain an MXene / nanocellulose / polydopamine composite material.

[0022] In some embodiments of the present invention, the MXene dispersion is added to the nanocellulose dispersion by slow dripping and stirring for 10 min to 60 min, preferably 20 min to 30 min. By stirring for a certain period of time, the nanocellulose with a high aspect ratio opens the stacked two-dimensional MXene material layered structure through self-assembly intercalation behavior, forming a stable MXene / nanocellulose dispersion.

[0023] In some embodiments of the present invention, after the dopamine monomer is fully dissolved and mixed in the MXene / nanocellulose dispersion, the pH is adjusted to 7-10, preferably 8-9, and more preferably 8.4-8.7 using a Tris buffer. The alkaline conditions of the aqueous environment affect the polymerization rate of dopamine. If the rate of dopamine oxidative polymerization is too fast, it will self-polymerize and nucleate to form larger polydopamine particles. If the polymerization rate is moderate, the polydopamine will form a film coating on the MXene and nanocellulose. The polymerization rate is optimal under slightly alkaline conditions.

[0024] In some embodiments of the present invention, the reaction temperature of the polydopamine-coated MXene material is 15°C to 50°C, preferably 20°C to 40°C, and more preferably 25°C to 30°C. The oxidative self-polymerization of the dopamine monomer can be accelerated by slight heating; in practice, it can be carried out directly at ambient temperature.

[0025] In some embodiments of the present invention, the polydopamine coating time of the MXene material is 1h to 24h, preferably 6h to 24h.

[0026] In some embodiments of the present invention, the concentration of the dispersion of the MXene material is 0.75 mg / mL. -1 ~6mg / mL -1 Preferred dosage: 1.25 mg / mL -1 ~3mg mL -1 .

[0027] In some embodiments of the present invention, in step S2, the liquid crystal monomer in the elastomer precursor is an acrylate liquid crystal monomer, including at least one monoacrylate-terminated liquid crystal (such as RM23, RM105, etc.) and a diacrylate-terminated liquid crystal (such as RM82, RM257).

[0028] In some embodiments of the present invention, in step S2, the thiol in the elastomer precursor includes at least one of 2,2′-(1,2-ethylenedioxy)diethylthiol (EDDET) and pentaerythritol tetramercaptoacetate (PETMP).

[0029] In some embodiments of the present invention, in step S2, the step of mixing the MXene / nanocellulose / polydopamine composite material with the liquid crystal elastomer precursor specifically involves dispersing the powder obtained after freeze-drying the obtained MXene / nanocellulose / polydopamine composite material dispersion into a tetrahydrofuran solvent, and then mixing it evenly with the liquid crystal elastomer precursor.

[0030] In some embodiments of the present invention, the MXene / nanocellulose / polydopamine composite powder is dispersed in tetrahydrofuran by ultrasonic, homogenization or oscillation treatment for a dispersion time of 10 min to 60 min, preferably 10 min to 30 min, and more preferably 15 min to 30 min.

[0031] In some embodiments of the present invention, in step S2, the step of forming liquid crystal oligomers by reacting is specifically as follows: the mixed precursor dispersion is protected from light and placed on a hot plate for stirring and reaction; the liquid crystal monomer in the precursor undergoes a Michael addition reaction with the thiol; and the liquid crystal monomer and the thiol undergo polymerization or crosslinking to form liquid crystal oligomers.

[0032] In some embodiments of the present invention, the temperature of the addition reaction is 20°C to 60°C, preferably 35°C to 50°C, and more preferably 45°C to 50°C.

[0033] In some embodiments of the present invention, the addition reaction takes place for 1 to 8 hours, preferably 3 to 5 hours, and more preferably 4 to 4.5 hours.

[0034] In some embodiments of the invention, the addition reaction is carried out in a closed and light-protected reaction vessel.

[0035] In some embodiments of the present invention, the temperature of the addition reaction is 20°C to 60°C, and the reaction time is 1 to 8 hours.

[0036] In some embodiments of the present invention, the elastomer precursor contains the catalyst di-n-propylamine (DPA). In practice, the catalyst is added to the tetrahydrofuran dispersion of the composite material and then added together with the precursor mixture.

[0037] In some embodiments of the present invention, the mass of the catalyst is 0.5 wt.% to 2 wt.% of the liquid crystal monomer, preferably 0.5 wt.% to 1.5 wt.%, more preferably 0.8 wt.% to 1 wt.%.

[0038] In some embodiments of the present invention, in step S2, the specific steps of the thermosetting of the liquid crystal oligomer are as follows: pouring the liquid crystal oligomer dispersion into a polytetrafluoroethylene mold, placing it in an oven to remove the solvent, and then peeling it off to obtain a liquid crystal oligomer film.

[0039] In some embodiments of the present invention, the thermosetting reaction temperature is 40°C to 80°C, preferably 40°C to 60°C, and more preferably 40°C to 45°C.

[0040] In some embodiments of the present invention, the thermosetting reaction time is 4h to 12h, preferably 8h to 10h, and more preferably 8h to 8.5h.

[0041] In some embodiments of the present invention, the specific steps of ultraviolet light polymerization of the liquid crystal oligomer are as follows: after stretching the oligomer film to form a nematic liquid crystal orientation, the remaining unreacted liquid crystal monomers acrylic acid end groups in the liquid crystal oligomer are subjected to a free radical polymerization reaction initiated by ultraviolet light to completely polymerize the liquid crystal oligomer and obtain a liquid crystal elastomer.

[0042] In some embodiments of the present invention, a stretched film with parallel and uniform orientation is formed, with a stretching ratio of 100% to 600%, preferably 400% to 600%, and more preferably 450% to 500%.

[0043] In some embodiments of the present invention, in order to permanently fix the orientation, the liquid crystal monomer in the liquid crystal precursor needs to exceed the thiol by 8 mol% to 15 mol%, preferably 10 mol% to 15 mol%, more preferably 10 mol% to 13 mol%.

[0044] In some embodiments of the present invention, in step S2, the thermosetting temperature is 40°C to 80°C, the reaction time is 4 to 12 hours, and the elongation is 100 to 600%.

[0045] In some embodiments of the present invention, the ultraviolet photopolymerization reaction contains a photoinitiator (DMPA). In practice, the photoinitiator is added directly to the liquid crystal precursor mixture and stored away from light.

[0046] In some embodiments of the present invention, the photoinitiator is 0.5 wt.% to 2 wt.% of the precursor mixture, preferably 0.5 wt.% to 1.5 wt.%, more preferably 0.8 wt.% to 1 wt.%.

[0047] In some embodiments of the present invention, the light intensity during ultraviolet (337nm) polymerization is 15mW cm⁻¹. -2 ~25mW cm -2 15mW cm is preferred -2 ~20mW cm -2 More preferably 18mW cm -2 ~20mW cm -2 .

[0048] In some embodiments of the present invention, the photopolymerization time is 10 min to 60 min, preferably 15 min to 30 min, and more preferably 15 min to 20 min.

[0049] In some embodiments of the present invention, in step S2, the ultraviolet light polymerization conditions are: 15–25 mW cm⁻¹ -2 Irradiate with 337nm ultraviolet light for 10–60 minutes.

[0050] A third aspect of the present invention is to provide the above-described liquid crystal elastomer in light-driven actuators, soft robots, artificial muscles, and their applications in underwater scenarios.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] The liquid crystal elastomer of this invention utilizes MXene as a photothermal conversion filler and mechanical reinforcement material by filling a liquid crystal polymer matrix with an MXene / nanocellulose / polydopamine composite material. Modification of polydopamine improves the dispersibility and synergistic photothermal conversion performance of MXene within the liquid crystal polymer. Nanocellulose ensures that polydopamine is uniformly coated on the surface of the MXene material, simultaneously enhancing the mechanical properties of the liquid crystal elastomer. The dense structure of the liquid crystal elastomer film protects the MXene material from oxidation. The preparation method is simple and easy to control, resulting in an elastomer with excellent light-driven and mechanical properties, suitable for applications such as light-driven actuators, soft robots, and artificial muscles, especially for underwater applications. Attached Figure Description

[0053] Figure 1 Transmission electron microscopy image and elemental analysis of the MXene / nanocellulose / polydopamine composite material of Example 1;

[0054] Figure 2 The UV-Vis absorption spectra of the MXene / nanocellulose / polydopamine composite material and its different components in Example 1 are shown.

[0055] Figure 3 Photographs of the liquid crystal elastomer of Example 1 and its thermal response changes;

[0056] Figure 4 This is a cross-sectional scanning electron microscope image of the liquid crystal elastomer of Example 1;

[0057] Figure 5 The UV-Vis absorption spectra of the blank control and liquid crystal elastomer films with different doped composite materials in Example 1 are shown.

[0058] Figure 6 To process the liquid crystal elastomer film in Example 1 through 1.6W cm -2 Temperature changes under 808nm infrared laser irradiation and comparisons between different components;

[0059] Figure 7 A comparison of the mechanical properties of the liquid crystal elastomer of Example 1 and the undoped liquid crystal elastomer;

[0060] Figure 8The results and photographs of the weight lifting experiment of the liquid crystal elastomer film in Example 1 are shown.

[0061] Figure 9 The liquid crystal elastomer film of Example 1 was subjected to 700mW cm -2 Self-driven behavior under 808nm infrared laser irradiation for different durations;

[0062] Figure 10 Comparative images of liquid crystal oligomers obtained in Comparative Example 1 and Example 1. Detailed Implementation

[0063] In the description of this invention, unless otherwise explicitly defined, terms such as heating, cleaning, and weighing should be interpreted broadly. Those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0064] In the description of this invention, references to terms such as "some embodiments" and "examples" indicate that the specific methods or materials described in connection with that embodiment or example are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiments or examples. Furthermore, the specific methods and materials described may be combined in any suitable manner in one or more embodiments or examples.

[0065] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to specific embodiments and accompanying drawings, but this does not constitute a limitation on the scope of protection of the present invention.

[0066] Unless otherwise specified, the raw materials used in the following examples can be obtained from conventional commercial sources; unless otherwise specified, the processes used are conventional processes in the art; the room temperature refers to 20-25°C; the MXene material in the following examples is Ti3C2 monolayer nanosheets; and the nanocellulose is cellulose nanocrystals.

[0067] Example 1

[0068] I. Preparation of MXene / nanocellulose / polydopamine composite materials

[0069] Weigh 20 mg of MXene dispersion (3 mg / mL) 1 ), slowly add dropwise to 60 mL of cellulose nanocrystal aqueous dispersion (0.5 wt.%), stir for 30 min, add 5 mg of dopamine hydrochloride (DA), adjust the pH of the aqueous dispersion to 8.5 using Tris, react for 24 h to obtain a dispersion of MXene / nanocellulose / polydopamine composite material, wash the dispersion and freeze-dry for two days to obtain a powdered composite material.

[0070] Figure 1 The image shows a transmission electron microscope (TEM) image of the composite material, revealing two-dimensional sheet-like MXene material and rod-shaped cellulose nanocrystals. Nitrogen elemental scanning analysis indicates that dopamine is attached to the MXene surface. Figure 2 The light absorption spectrum of the composite material and its various components is shown in the ultraviolet-visible light absorption spectrum. The absorption peak at around 800 nm proves that the material has infrared light absorption properties.

[0071] II. Preparation of MXene / nanocellulose / polydopamine-filled liquid crystal elastomers

[0072] Weigh a certain amount of the composite material and add 1.8 mL of tetrahydrofuran and sonicate in a water bath for 15 min. Then add 6 μL of the catalyst dipropylamine (DPA) for later use.

[0073] 757 mg of liquid crystal monomer 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene (RM257), 191.8 mg of chain extender 2,2′-(1,2-ethylenedioxy)bis(ethylenedioxy)diethylthiol (EDDET), 30.5 mg of crosslinking agent pentaerythritol tetramercaptoacetate (PETMP), and 9.8 mg of photoinitiator benzoin dimethyl ether (DMPA) were weighed into a light-protected sample bottle. The above-mentioned tetrahydrofuran dispersion of the composite material was added to the bottle and stirred evenly. The mixture was then stirred at 50 °C for 4.5 h in a sealed state to obtain oligomers.

[0074] The oligomer dispersion was transferred to a polytetrafluoroethylene (PTFE) mold. After removing air bubbles by vacuuming in an oven, it was heat-cured at 40°C for 4.5 hours. The film was then peeled off the mold and dried under vacuum at 60°C for 8 hours. The completely solvent-free film passed a 500% stretch test and yielded a 19mW cm⁻¹ test result. -2 Irradiate with 337nm ultraviolet light for 15 minutes to obtain the desired liquid crystal elastomer.

[0075] like Figure 3 As shown, the prepared liquid crystal elastomer film is uniformly black and can be actuated by contraction under heating stimulation on a hot stage. This is illustrated by a scanning electron microscope image of its cross-section. Figure 4 It can be seen that the dense structure of the liquid crystal film enables the encapsulation of MXene material, protecting MXene from water and oxygen corrosion, and improving its stability as an actuator, making it particularly suitable for underwater environments.

[0076] Figure 5The images show the UV-Vis spectra of the liquid crystal film and its components (UV-Vis absorption spectra of the blank control and liquid crystal elastomer films doped with different components). Similarly, there is an absorption spectrum at the 800nm ​​peak, indicating that the film has the ability to absorb infrared light and is uniformly dispersed. In particular, the liquid crystal film of the composite material has a higher absorption than the liquid crystal film of the pure MXene material, which is due to the synergistic photothermal effect of PDA (polydopamine).

[0077] like Figure 6 In a liquid crystal elastomer film doped with 1 wt.% MXene / nanocellulose / polydopamine composite material, 1.6 W cm⁻¹ -2 When irradiated by 808nm infrared absorbed light, the liquid crystal elastomer converts the infrared light into heat, which can reach up to 150℃. Figure 7 The results showed that the fracture stress of the liquid crystal elastomer doped with 1 wt.% MXene / nanocellulose / polydopamine composite material was twice that of the undoped blank liquid crystal matrix, reaching approximately 12 MPa, significantly improving its mechanical properties. This enhanced mechanical property makes it possible for liquid crystal elastomers to be used as artificial muscles. Figure 8 This indicates that a liquid crystal elastomer doped with 1 wt.% of an MXene / nanocellulose / polydopamine composite material can lift a weight approximately 1500 times its own weight and maintain stable operation for 10 cycles. Due to the excellent photothermal conversion properties of the composite material, the film responds very quickly to infrared radiation, and the properties of liquid crystals make liquid crystal actuation highly flexible, such as... Figure 9 The study demonstrated that under programmed controlled stimulation by infrared laser irradiation, a liquid crystal elastomer film underwent changes from a planar shape to a flipped shape and then to an arched shape, indicating its potential as a soft robot.

[0078] Example 2

[0079] I. Preparation of MXene / nanocellulose / polydopamine composite materials

[0080] Weigh 20 mg of MXene dispersion (2.25 mg / mL) -1 The MXene / nanocellulose / polydopamine composite material was slowly added dropwise to 60 mL of an aqueous dispersion of cellulose nanocrystals (0.5 wt.%), stirred for 1 h, and then 5 mg of dopamine hydrochloride (DA) was added. The pH of the aqueous dispersion was adjusted to 8.5 using Tris, and the reaction was allowed to proceed for 12 h to obtain a dispersion of the MXene / nanocellulose / polydopamine composite material. After washing the dispersion, it was freeze-dried for two days to obtain a powdered composite material.

[0081] II. Preparation of MXene / nanocellulose / polydopamine-filled liquid crystal elastomers

[0082] Weigh a certain amount of the composite material and add 1.8 mL of tetrahydrofuran and sonicate in a water bath for 30 min. Then add 6 μL of the catalyst dipropylamine (DPA) for later use.

[0083] 191.8 mg of chain extender 2,2′-(1,2-ethylenedioxy)diethylthiol (EDDET), 30.5 mg of crosslinking agent pentaerythritol tetramercaptoacetate (PETMP), and 9.8 mg of photoinitiator benzoin dimethyl ether (DMPA) were weighed into light-proof sample bottles. The above-mentioned tetrahydrofuran dispersion of the composite material was added into the bottle and stirred evenly. The mixture was then stirred at 50°C for 4.5 h in a sealed state to obtain oligomers.

[0084] The oligomer dispersion was transferred into a polytetrafluoroethylene (PTFE) mold. After removing air bubbles by vacuuming in an oven, it was heat-cured at 40°C for 4 hours. The film was then peeled off the mold and dried under vacuum at 60°C for 10 hours. The completely solvent-free film passed a 500% stretch test and yielded a 19mW cm⁻¹ test result. -2 Irradiate with 337nm ultraviolet light for 15 minutes to obtain the desired liquid crystal elastomer.

[0085] Similar to Example 1, the liquid crystal elastomer prepared in this example is uniformly black and has photothermal response properties and mechanical enhancement properties.

[0086] Example 3

[0087] I. Preparation of MXene / nanocellulose / polydopamine composite materials

[0088] Weigh 20 mg of MXene dispersion (3 mg / mL) -1 The MXene / nanocellulose / polydopamine composite material was slowly added dropwise to 60 mL of an aqueous dispersion of cellulose nanocrystals (0.5 wt.%), stirred for 10 min, and then 7 mg of dopamine hydrochloride (DA) was added. The pH of the aqueous dispersion was adjusted to 8.7 using Tris, and the reaction was carried out for 10 h to obtain a dispersion of the MXene / nanocellulose / polydopamine composite material. After washing the dispersion, it was freeze-dried for two days to obtain a powdered composite material.

[0089] II. Preparation of MXene / nanocellulose / polydopamine-filled liquid crystal elastomers

[0090] Weigh a certain amount of the composite material and add 1.8 mL of tetrahydrofuran and sonicate in a water bath for 30 min. Then add 6 μL of the catalyst dipropylamine (DPA) for later use.

[0091] 191.8 mg of chain extender 2,2′-(1,2-ethylenedioxy)diethylthiol (EDDET), 33 mg of crosslinking agent pentaerythritol tetramercaptoacetate (PETMP), and 10 mg of photoinitiator benzoin dimethyl ether (DMPA) were weighed into light-proof sample bottles. The above-mentioned tetrahydrofuran dispersion of the composite material was added into the bottle and stirred evenly. The mixture was then stirred and reacted at room temperature for 5 h in a sealed state to obtain oligomers.

[0092] The oligomer dispersion was transferred into a polytetrafluoroethylene (PTFE) mold. After removing air bubbles by vacuuming in an oven, it was heat-cured at 40°C for 6 hours. The film was then peeled off the mold and dried under vacuum at 60°C for 5 hours. The completely solvent-free film passed a 600% stretch test and yielded a 19mW cm⁻¹ test result. -2 Irradiate with 337nm ultraviolet light for 10 minutes to obtain the desired liquid crystal elastomer.

[0093] Similar to Example 1, the liquid crystal elastomer prepared in this example is uniformly black and has photothermal response properties and mechanical enhancement properties.

[0094] Comparative Example 1

[0095] The difference between this comparative example and Example 1 is that the Michael addition reaction time after obtaining the precursor dispersion was adjusted to 30 min (or direct thermosetting was performed). Other operations were the same as in Example 1.

[0096] The results of this comparative example showed that the liquid crystal oligomers were as follows: Figure 10 As shown, the MXene / nanocellulose / polydopamine composite material exhibited severe agglomeration in the matrix, while Example 1 showed a uniform black appearance. This is mainly because reducing the degree of Michael addition reaction in the precursor dispersion significantly reduced the entanglement and interaction of the generated liquid crystal oligomers with the composite material. Consequently, during thermosetting, the volatilization of tetrahydrofuran carried the composite material in the liquid crystal matrix, exacerbating its agglomeration. Therefore, the inability to obtain a uniformly dispersed liquid crystal elastomer reduces photothermal conversion performance and may even weaken the mechanical properties of the liquid crystal matrix itself, greatly reducing the service life and performance of the liquid crystal elastomer.

[0097] In summary, it can be seen that in the liquid crystal elastomer of this invention, by adding an MXene / nanocellulose / polydopamine composite material to the liquid crystal polymer matrix, MXene is used as a photothermal conversion filler and mechanical reinforcement material; the modification of polydopamine improves the dispersion of MXene in the liquid crystal polymer and enhances its synergistic photothermal conversion performance; nanocellulose ensures that polydopamine is uniformly coated on the surface of the MXene material, thereby enhancing the mechanical properties of the liquid crystal elastomer; and the dense structure of the liquid crystal elastomer film protects the MXene material from oxidation. Compared with other actuators based on MXene materials, the resulting liquid crystal elastomer has a dense structure, excellent photothermal conversion performance, rapid infrared response, flexible actuation, and significantly improved mechanical properties, up to 2 times. This improvement in mechanical properties makes it possible for the liquid crystal elastomer to become an artificial muscle, enabling it to lift weights approximately 1500 times its own weight and sustain stable cycles for 10 cycles. The liquid crystal elastomer of this invention can be applied to light-driven actuators, soft robots, artificial muscles, etc., and is particularly suitable for underwater applications.

[0098] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be noted that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A liquid crystal elastomer, characterized in that: The liquid crystal elastomer includes a liquid crystal polymer matrix and an MXene / nanocellulose / polydopamine composite material dispersed therein; The liquid crystal polymer matrix is ​​formed by crosslinking the liquid crystal monomer 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene; The MXene / nanocellulose / polydopamine composite material includes MXene, nanocellulose, and polydopamine coated on the MXene and nanocellulose; The method for preparing the liquid crystal elastomer includes the following steps: S1 prepares MXene / nanocellulose / polydopamine composite materials; In the MXene / nanocellulose / polydopamine composite material, the mass ratio of MXene to nanocellulose is 1:4.5 to 10, and the polydopamine is obtained by the oxidative self-polymerization of dopamine monomer, wherein the mass ratio of dopamine monomer to MXene is 1:0.05 to 0.

2. S2 is used to prepare liquid crystal elastomers; The MXene / nanocellulose / polydopamine composite material is mixed with an elastomer precursor, and a Michael addition reaction is carried out to form a liquid crystal oligomer; the Michael addition reaction is carried out at a temperature of 20℃ to 60℃ and a reaction time of 1 to 8 hours; the elastomer precursor includes a liquid crystal monomer and a thiol, wherein the liquid crystal monomer is 1,4-bis-[4-(3-acryloyloxypropoxy)benzoyloxy]-2-methylbenzene; The liquid crystal oligomer is thermosetting, stretched and oriented, and then polymerized under ultraviolet light to obtain the liquid crystal elastomer. The amount of the MXene / nanocellulose / polydopamine composite material added to the liquid crystal elastomer is 0.1-1 wt%.

2. The liquid crystal elastomer according to claim 1, characterized in that: In step S2, the elastomer precursor contains the catalyst di-n-propylamine.

3. The liquid crystal elastomer according to claim 1, characterized in that: In step S2, the thermosetting temperature is 40℃~80℃, the reaction time is 4~12h, and the stretching elongation is 100~600%.

4. The liquid crystal elastomer according to claim 1, characterized in that: In step S2, the ultraviolet light polymerization conditions are: 15–25 mW·cm⁻¹ -2 Irradiate with 337nm ultraviolet light for 10–60 minutes.

5. The liquid crystal elastomer according to any one of claims 1 to 4 in light-driven actuators, soft robots and artificial muscles, and their application in underwater scenarios.

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