An ion-conductive cholesteric liquid crystal elastomer and its preparation method and application

Abstract

The present invention discloses an ion-conductive cholesteric liquid crystal elastomer and its preparation method and application. The ion-conductive cholesteric liquid crystal elastomer provided by the present invention is prepared by introducing a silane coupling agent between a cholesteric liquid crystal elastomer network and an ion gel network. The specific preparation process includes the preparation of an ionic liquid, the preparation of an ion gel, the surface modification of the ion gel, and the preparation of an ion-conductive cholesteric liquid crystal elastomer. Due to its mechanochromic and ion-conductive properties, the prepared cholesteric liquid crystal elastomer can perform optical visualization and electrical signal response under mechanical force. In particular, by simply stacking the ion-conductive cholesteric liquid crystal elastomers, a capacitive pressure sensor can be constructed to achieve real-time optoelectronic dual-signal sensing of pressure. The ion-conductive cholesteric liquid crystal elastomer provided by the present invention has important application values in the fields of advanced artificial skin, human health monitoring, human-computer interaction, and intelligent robots, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of functional liquid crystal materials, and particularly relates to an ion-conductive cholesteric liquid crystal elastomer, a preparation method thereof, and an application thereof. The prepared cholesteric liquid crystal elastomer has the characteristics of force-induced color change and ion conductivity, can respond to external forces in real time with optical signals and electrical signals, and its circular polarization reflection color and conductivity can be regulated by changing the content of chiral agents and ionic liquids, etc. Based on this ion-conductive cholesteric liquid crystal elastomer, a capacitive sensor can also be constructed to realize visual and digital sensing of pressure. The invention is expected to be applied in the fields of artificial skin, intelligent robots, and human-computer interaction, etc. Background Art

[0002] The skin is an organ that directly contacts the external environment of an organism. It can sense environmental information and encode it into bioelectric signals, and transmit them to the nervous system through ion transport, so as to sensitively sense changes in the external environment. By mimicking the sensing function of biological skin, researchers have developed artificial skins, such as electronic skins and ionic skins, which have broad application prospects in emerging fields such as health monitoring, human-computer interaction, intelligent robots, and prosthetics. It is worth noting that some organisms can also respond to the surrounding environment by actively changing the skin color for better survival and reproduction. For example, chameleons can convert external stimuli into electrical signals to adjust the lattice spacing between guanine nanocrystals in the iris cells of the dermis layer, thereby adjusting the skin color. Inspired by natural organisms, the preparation of artificial skins with optoelectronic dual-signal sensing functions has become a research hotspot, and how to develop materials with both bright structural colors and excellent conductivity is a key scientific problem in this field. Among many material systems, cholesteric liquid crystal elastomers (CLCEs) with both polymer elasticity and circular polarization reflection color exhibit unique advantages and have attracted wide attention. Due to their adjustable periodic helical nanostructures, large elastic anisotropy, sensitive stimulus responsiveness, and simple preparation methods, CLCEs have been developed and used to manufacture optical materials and devices. Although many progresses have been made in the field of bionic color-changing camouflage with CLCEs at present, the preparation of conductive CLCEs with sensing functions is still a formidable challenge.

[0003] Based on this, we propose an ion-conductive cholesteric liquid crystal elastomer. This material not only has dynamic force-induced color change characteristics and excellent ion conductivity, but also can construct a capacitive sensor through simple stacking to realize real-time optoelectronic dual-signal response to pressure. The invention is expected to lay a foundation for the development of fields such as artificial skin, intelligent robots, and human-computer interaction. Summary of the Invention

[0004] The object of the present invention is to provide an ion-conductive cholesteric liquid crystal elastomer and a preparation method thereof. By using a silane coupling agent to perform surface modification on an ionogel, and through an anisotropic volatilization method of a two-stage thiol / acrylate Michael addition-photopolymerization reaction, in-situ self-assembly of CLCE is carried out on the surface of the ionogel, thereby obtaining an ion-conductive cholesteric liquid crystal elastomer (iCLCE).

[0005] Another object of the present invention is to provide an application of the ion-conductive cholesteric liquid crystal elastomer. Since a covalent bond is introduced between the CLCE and the ionogel network interface, the iCLCE has a strong interfacial binding strength. Benefiting from excellent mechanochromic properties and high ionic conductivity, the cholesteric liquid crystal elastomer prepared by the present invention can achieve optical visualization and electrical signal response. Due to its unique bilayer structure, simply stacking the iCLCE can construct a capacitive sensor to achieve real-time optoelectronic dual-signal response to pressure.

[0006] The technical solution adopted to achieve the object of the present invention is as follows:

[0007] A preparation method of an ion-conductive cholesteric liquid crystal elastomer, the preparation method comprising the following steps:

[0008] Step 1) Preparation of ionic liquid

[0009] After dissolving, stirring, and standing for layering of an organic cation compound and an anion compound, taking the transparent oily liquid, washing to remove residues, and heating and drying to obtain a polymerizable ionic liquid; replacing the organic cation compound, and obtaining a solvent ionic liquid through the same preparation process as above.

[0010] Step 2) Preparation of ionogel

[0011] Mixing the polymerizable ionic liquid and the solvent ionic liquid prepared in step 1) in a predetermined ratio, adding a crosslinking agent, a silane coupling agent, and a photoinitiator and mixing evenly, pouring into a mold, and performing ultraviolet photopolymerization under nitrogen protection to obtain a transparent ionogel;

[0012] Step 3) Surface modification of ionogel

[0013] Dropping a silane coupling agent solution with a predetermined concentration onto the surface of the ionogel prepared in step 2), placing at room temperature, washing the surface of the ionogel, and storing in a low-humidity environment condition after complete drying;

[0014] Step 4) Preparation of iCLCE

[0015] Using the ion gel obtained in step 3) as the substrate, in-situ preparation of iCLCE is carried out by the anisotropic evaporation method: Dissolve the polymerizable liquid crystal monomer and the chiral agent in a solvent, heat to completely dissolve the polymerizable liquid crystal monomer, and after cooling to room temperature, add a chain extender, a crosslinking agent, a photoinitiator and a catalyst and mix evenly. After vacuum drying and degassing, a precursor is obtained. Pour the precursor onto the ion gel surface-modified by the silane coupling agent prepared in step 3), and place it at room temperature. After the first-stage Michael addition is completed, carry out the second-stage free radical photopolymerization reaction to obtain an iCLCE with an ion gel layer below and a CLCE layer above.

[0016] In the above technical solution, the organic cation raw material for preparing the polymerizable ionic liquid in step 1) is selected from one or more of acryloyloxyethyl trimethyl ammonium chloride (ATAC Cl) and methacryloyloxyethyl trimethyl ammonium chloride (MATAC Cl), and the anion raw material is selected from one or more of lithium bis(trifluoromethanesulfonylimide) (Li TFSI), lithium tetrafluoroborate (Li BF4), and lithium hexafluorophosphate (Li PF6).

[0017] In the above technical solution, the organic cation for preparing the solvent ionic liquid in step 1) is selected from 4111 one or more of butyl trimethyl ammonium chloride (N 4111 Cl) and butyl trimethyl ammonium bromide (N

[0018] Br), and the anion raw materials for preparing the solvent ionic liquid include but are not limited to one or more of lithium bis(trifluoromethanesulfonylimide) (Li TFSI), lithium tetrafluoroborate (Li BF4), and lithium hexafluorophosphate (Li PF6).

[0019]

[0020] In step 2), ultrasonic mixing is carried out for 20 - 40 min. The mold used is a polytetrafluoroethylene mold with a length of 35 - 50 mm, a width of 25 - 40 mm, and a depth of 2 - 5 mm. The light source for ultraviolet photopolymerization is a UV light source with a wavelength of 365 nm and a light intensity of 5 - 200 mW / cm 2 , and the polymerization time is 60 s - 1800 s.

[0021] In the above technical solution, the preparation process of the silane coupling agent solution in step 3) is as follows: Deionized water and absolute ethanol are mixed in a certain ratio, and a silane coupling agent is added. Among them, the ratio of deionized water to absolute ethanol is 1:1 to 1:0.5, and the concentration range of the silane coupling agent solution is 1.0 to 5.0 wt%; the dropping content of the silane coupling agent solution is 100 to 500 μL, and the surface of the ion gel is cleaned 5 - 10 times.

[0022] In the above technical solution, the silane coupling agent used in step 3) is selected from one or more of 3-(methacryloyloxy)propyltrimethoxysilane (TMSPMA), vinyltrimethoxysilane (A-171), and vinyltris(2-methoxyethoxy)silane (A-172).

[0023] In the above technical solution, in the raw materials for preparing iCLCE in step 4), the total molar amount of the acryloyloxy groups of the polymerizable liquid crystal monomer and the chiral agent is in a ratio of 1:1 to 11:10 to the total molar amount of the mercapto groups of the chain extender and the crosslinking agent; the molar ratio of the crosslinking agent to the chain extender is 1:19 to 1:4;

[0024] The boiling point of the solvent for dissolving the polymerizable liquid crystal monomer and the chiral agent does not exceed 130 °C, and the solvent is selected from one or more of toluene, dichloromethane, and dichloroethane.

[0025] The chain extender is a dimercapto monomer, selected from one or more of 2,2-(ethylenedioxy)diethanethiol (EDDET), 1,3-propanedithiol, and 1,6-hexanedithiol;

[0026] The crosslinking agent includes a trithiol monomer and a tetrathiomonomer, selected from one or more of 2-ethyl-2-[(3-mercapto-1-oxopropoxy)methyl]-1,3-propanediyl bis(3-mercaptopropionate) (TTMP) and pentaerythritol tetrakis(3-mercaptopropionate) (PETMP);

[0027] The catalyst for catalyzing the first-stage Michael addition reaction is selected from one or more of dipropylamine (DPA), triethylamine, and n-hexylamine;

[0028] The photoinitiator for initiating the second-stage free radical photopolymerization reaction is selected from one or more of 2,2-dimethoxy-2-phenylacetophenone (Irg651), phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (Irg 819), and 2-hydroxy-2-methyl-1-phenyl-1-propanone (Irg 1173).

[0029] The reaction temperature of the first-stage polymerization reaction is 15 °C to 35 °C, the reaction time is 18 to 36 h, the light source used in the second-stage photopolymerization reaction is a UV light source with a wavelength of 365 nm, and the light intensity is 5 to 200 mW / cm 2, the polymerization time is 60 s to 1800 s.

[0030] In the above technical solution, the polymerizable liquid crystal monomer is selected from one or more of the compounds represented by formula (I),

[0031]

[0032] In formula (I), A and B each independently represent an aromatic ring (such as 1,4 - benzene ring, 2,5 - pyrimidine ring, 1,2,6 - naphthalene ring), or an alicyclic hydrocarbon (such as trans - 1,4 - cyclohexane), and A and B may contain side groups, which are halogen, or cyano, or methyl; x and y are each 0 to 4; Z is an ester group, or an alkynyl group, or an alkyl group, or directly connected, or a nitrogen - nitrogen double bond, or an ether bond; R1 is an alkyl group containing 1 to 16 carbon atoms; R2 is an alkyl group containing 1 to 16 carbon atoms, or an acryloyloxy group containing 1 to 16 carbon atoms, or a siloxanyl group containing 1 to 16 atoms, or an ester group, or a cyano group, or a halogen, or an isothiocyanato group, or a nitro group.

[0033] In the above technical solution, the polymerizable liquid crystal monomer includes a mono - reactive - functionality liquid crystal monomer and / or a bi - reactive - functionality liquid crystal monomer, the phase transition temperature is 30 °C to 180 °C, and it is selected from one or more of the following formulas:

[0034]

[0035] Among them, x and y are each 1 to 16, and A and B each independently represent hydrogen, halogen, alkyl, alkoxy, carboxyl, cyano, etc.

[0036] On the other hand, the present invention also includes an ion - conductive cholesteric liquid crystal elastomer prepared by the above method.

[0037] On the other hand, the present invention also includes the application of the ion - conductive cholesteric liquid crystal elastomer in an optoelectronic dual - signal response sensor.

[0038] The optical visualization and electrical signal response process of the ion - conductive cholesteric liquid crystal elastomer is as follows:

[0039] 1) During the processes of stretching, bending, and pressing, the thickness of the iCLCE film in the observation direction, that is, perpendicular to its plane, decreases, the pitch decreases, and according to Bragg's reflection law λ = n×p×cosθ (where λ is the reflection wavelength, n is the average refractive index, p is the pitch, and θ is the angle of the incident light), its reflection wavelength undergoes a blue shift.

[0040] 2) During the processes of stretching and bending, the length of the iCLCE in the ion - conduction direction increases, the cross - sectional area decreases, the resistance increases, and the conductivity decreases; during the pressing process, the thickness of the intermediate layer CLCE decreases, and the capacitance of the sensor increases.

[0041] On the other hand, the present invention also includes the application of the ion-conductive cholesteric liquid crystal elastomer in human motion monitoring and human-machine interaction. Preferably, the ion-conductive cholesteric liquid crystal elastomer can be applied to fields such as artificial skin and intelligent robots.

[0042] On the other hand, a capacitive sensor is composed of two superimposed ion-conductive cholesteric liquid crystal elastomers, forming a four-layer structure. The four-layer structure is respectively the first layer of CLCE, the second layer of ion gel, the third layer of CLCE, and the fourth layer of ion gel. The first layer of CLCE provides structural color, the third layer of CLCE serves as a dielectric, and the second layer of ion gel and the fourth layer of ion gel serve as flexible conductive layers and are connected to wires.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] 1) The present invention provides a general preparation strategy. By introducing a silane coupling agent, the CLCE and ion gel networks are integrated together, significantly increasing the interfacial bonding strength between the bilayers. At the same time, by using the methods of anisotropic volatilization and in-situ photopolymerization, the CLCE can well complete the self-assembly of the helical structure and maintain a uniform and bright circularly polarized reflection color.

[0045] 2) The iCLCE provided by the present invention can perform dynamic reversible color regulation in the entire visible light spectrum under the action of force, and has sensitive optical signal sensing performance. At the same time, it mimics the ion conduction mechanism of biological skin and has stable and reliable ion conduction and electrical signal sensing performance.

[0046] 3) The iCLCE provided by the present invention has a unique bilayer structure. By simply stacking it, a capacitive pressure sensor can be constructed.

[0047] 4) The applications of the ion-conductive cholesteric liquid crystal elastomer provided by the present invention include but are not limited to the fields of pressure visualization and bionic skin. The applications in the fields of intelligent robots, human health monitoring, human-machine interaction, etc. are all within the protection scope of this patent. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 Schematic diagram of the preparation process for synthesizing the ion-conductive cholesteric liquid crystal elastomer in Example 1;

[0049] Figure 2 Cross-sectional microstructure of the ion-conductive cholesteric liquid crystal elastomer under a scanning electron microscope (SEM) in Example 1;

[0050] Figure 3 Interfacial bonding strength of the ion-conductive cholesteric liquid crystal elastomer at different silane coupling agent contents;

[0051] Figure 4 is the stress-strain curve of the ion-conductive cholesteric liquid crystal elastomer;

[0052] Figure 5 is the ionic conductivity of the ion-conductive cholesteric liquid crystal elastomer;

[0053] Figure 6 are (a) color change and (b) reflection spectrum during the stretching process of the ion-conductive cholesteric liquid crystal elastomer;

[0054] Figure 7 is the schematic diagram of circularly polarized reflection of the ion-conductive cholesteric liquid crystal elastomer;

[0055] Figure 8 is the relative resistance change during the stretching process of the ion-conductive cholesteric liquid crystal elastomer;

[0056] Figure 9 are (a) color change and (b) reflection spectrum during the bending process of the ion-conductive cholesteric liquid crystal elastomer;

[0057] Figure 10 is the relative resistance change during the bending process of the ion-conductive cholesteric liquid crystal elastomer;

[0058] Figure 11 are (a) color change and (b) reflection spectrum during the pressing process of the capacitive sensor;

[0059] Figure 12 is the relative capacitance change during the pressing process of the capacitive sensor. Detailed implementation manners

[0060] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0061] Embodiment 1

[0062] A preparation method of an ion-conductive cholesteric liquid crystal elastomer includes the following steps:

[0063] (1) Weigh 2.18 g of ATAC solution and 2.93 g of Li[TFSI], add them to a beaker containing 10 mL of deionized water, and vigorously stir with a magnetic stirrer at room temperature for 2 h. Let it stand for stratification, and take the lower transparent oily liquid. Subsequently, wash it 5 times with deionized water to remove LiCl and other residues, and then place it in a vacuum drying oven at 70 °C for 12 h to dry and remove water, thus obtaining the polymerizable ionic liquid [ATAC][TFSI]. Take 1.41 g of [N 4111 Cl to replace the ATAC solution, and through the same preparation process as above, the solvent ionic liquid [N4111 [TFSI].

[0064] (2) Weigh 438.4 mg of [ATAC][TFSI] (1 mmol) and 297.3 mg of [N 4111 [TFSI] (0.75 mmol) into a glass bottle, add 1.0 μL of crosslinker PEGDA, 0.2 μL of silane coupling agent TMSPMA and 2.0 μL of photoinitiator DEAP, and ultrasonicate for 20 min to fully mix the components. Then pour the precursor into a customized polytetrafluoroethylene mold. Under N2 protection, carry out ultraviolet polymerization for 600 s to obtain a transparent ion gel network.

[0065] (3) Mix deionized water and absolute ethanol in a volume ratio of 1:1, add TMSPMA monomer, and prepare a 2 wt% TMSPMA solution. Take 200 μL of the 2 wt% TMSPMA water / ethanol solution and drop it on the surface of the ion gel network, and place it at room temperature for 12 h. Then wash the modified ion gel network with absolute ethanol, store it in a lower humidity environment after complete drying.

[0066] (4) Weigh 630 mg of RM257 and 29 mg of LC756 and dissolve them in 400 mg of toluene solvent, and heat at 80 °C to completely dissolve the monomers. After cooling to room temperature, add 155 mg of EDDET, 36.7 mg of PETMP and 4 mg of Irg 651. Add 180 mg of diluted DPA solution (toluene:DPA = 50:1), stir the mixed solution at room temperature for 5 min to mix it evenly, and then place it in a vacuum drying oven to remove bubbles. Then pour the precursor onto the ion gel network, place it in a fume hood at room temperature for 24 h, and wait for the toluene solvent to completely volatilize. Finally, irradiate it with ultraviolet light of 20 mW / cm 2 for 60 s for curing to obtain an ion-conductive cholesteric liquid crystal elastomer with an ion gel network as the lower layer and CLCE as the upper layer. The schematic diagram of the preparation process is as Figure 1 shown.

[0067] The structural formulas of the reactants used in this example are as follows:

[0068]

[0069] Figure 2 is the microstructure of iCLCE under SEM. It can be seen from the figure that the interface between the bilayer structures is tightly combined, and the upper layer CLCE has obvious layered textures.

[0070] Figure 3The interfacial bonding strength of iCLCE under the action of different silane coupling agent contents. It can be seen from the figure that with the increase of the content of TMSPMA, the interfacial bonding strength of iCLCE first increases and then decreases. When the content of TMSPMA is 0.01 - 0.1% v / w, the interfacial bonding strength of the bilayer structure increases significantly, about 2.4 times that of the sample without TMSPMA.

[0071] Figure 4 For the ionic conductivity test of iCLCE, this figure shows that with the increase of the content of [N 4111 [TFSI], the ionic conductivity of iCLCE increases significantly from 1.66×10 -6 S cm -1 to 8.67×10 -5 S cm -1 , indicating that the ionic conductivity of iCLCE can be improved by increasing the content of the solvent ionic liquid.

[0072] Figure 5 For the stress-strain curve of iCLCE, it can be seen that compared with the original CLCE, the fracture strain of iCLCE remains almost unchanged, and the tensile strength decreases with the increase of the ionic gel thickness.

[0073] Example 2

[0074] An ionic conductive cholesteric liquid crystal elastomer is applied to tensile and bending sensing, including the following steps:

[0075] (1) Weigh 2.34 g of MATAC solution and 0.94 g of LiBF4, add them to a beaker containing 10 mL of deionized water, and vigorously stir with a magnetic stirrer at room temperature for 2 h. Let it stand for stratification, and take the lower transparent oily liquid. Subsequently, wash it 5 times with deionized water to remove LiCl and other residues, and then place it in a vacuum drying oven at 70 °C for 12 h to dry and remove water, thus obtaining the polymerizable ionic liquid [MATAC]BF4. Take 1.41 g of [N 4111 Cl to replace the MATAC solution, and through the same preparation process as above, the solvent ionic liquid [N 4111 BF4 is obtained.

[0076] (2) Weigh 259.0 mg of [MATAC]BF4 (1 mmol) and 101.5 [N 4111 BF4 (0.5 mmol) in a glass bottle, add 0.05 μL of silane coupling agent A-171 and 1.0 μL of photoinitiator DEAP, and ultrasonicate for 20 min to fully mix each component. Then pour the precursor into a customized polytetrafluoroethylene mold. Under N2 protection, ultraviolet light polymerization is carried out for 1200 s to obtain a gel-like transparent polyionic liquid film.

[0077] (3) Mix deionized water and absolute ethanol in a volume ratio of 1:0.5, add A-171, and prepare a 4 wt% A-171 solution. Take 400 μL of the 4 wt% A-171 water / ethanol solution and drop-coat it on the surface of the ionic gel network, and leave it at room temperature for 12 h. Then wash the modified ionic gel network with absolute ethanol, store it in a lower humidity environment after complete drying.

[0078] (4) Weigh 630 mg of RM257 and 29 mg of LC756 and dissolve them in 400 mg of toluene solvent, and heat at 80 °C to completely dissolve the monomers. After cooling to room temperature, add 155 mg of EDDET, 36.7 mg of PETMP and 4 mg of Irg 651. Add 180 mg of the diluted DPA solution (toluene:DPA = 50:1), stir the mixed solution at room temperature for 5 min to make it evenly mixed, and then place it in a vacuum drying oven to remove bubbles. Then pour the precursor onto the ionic gel network and leave it at room temperature in a fume hood for 24 h. Finally, irradiate it with ultraviolet light at 20 mW / cm 2 for 60 s for curing to obtain an ion-conductive cholesteric liquid crystal elastomer with an ionic gel network as the lower layer and CLCE as the upper layer.

[0079] (5) Use an optical fiber spectrometer to measure the reflection wavelength of iCLCE during the stretching process, and record its dynamic color change through a camera; measure the change in the relative resistance signal of iCLCE during the stretching process by combining a universal testing machine and a digital bridge, and calculate its sensitivity. Stick the iCLCE sample on the finger joint of the prosthetic hand and record the color and resistance changes at different bending angles.

[0080] The structural formulas of the reactants used in this example are as follows:

[0081]

[0082] Figure 6 (a) Color change and (b) reflection spectrum during the stretching process of iCLCE. It can be found from the figure that during the stretching process, iCLCE shows a dynamic color change, gradually changing from red to green and then to blue, and its corresponding reflection spectrum gradually undergoes a blue shift, and the reflection peak wavelength changes from 648 nm at the initial stage to 472 nm at 140% strain.

[0083] Figure 7 is the schematic diagram of the circular polarization reflection principle of iCLCE. The cholesteric liquid crystal elastomer has a layered helical nanostructure, and its circular polarization reflection conforms to Bragg's law: λ = n × p × cosθ, where λ is the reflection wavelength, n is the average refractive index, p is the pitch, and θ is the angle of the incident light. During the stretching process, the thickness of the CLCE film decreases and the pitch becomes smaller, resulting in a blue shift of the reflection wavelength.

[0084] Figure 8 is the relative resistance change during the stretching process of iCLCE. It can be seen that during the stretching process, the resistance of iCLCE continuously increases with the increase of strain, and the resistance change is linearly correlated with strain. The strain sensitivity coefficient GF is 2.0.

[0085] Figure 9 are (a) color change pictures and (b) reflection spectra during the bending process of iCLCE. It can be seen that as the finger bending angle increases, the color of iCLCE gradually undergoes a blue shift, and the reflection peak wavelength gradually decreases.

[0086] Figure 10 is the relative resistance change during the bending process of iCLCE. The relative resistance of iCLCE increases stepwise with the increase of the bending angle, indicating that iCLCE can accurately identify finger bending and has excellent electrical signal sensing performance.

[0087] Example 3

[0088] The ionic conductive cholesteric liquid crystal elastomer is used to construct a capacitive pressure sensor, including the following steps:

[0089] (1) Weigh 2.18 g of ATAC solution and 2.93 g of Li[TFSI], add them to a beaker containing 10 mL of deionized water, and use a magnetic stirrer to stir vigorously at room temperature for 2 h. Let it stand for layering, and take the lower transparent oily liquid. Subsequently, wash it 5 times with deionized water to remove LiCl and other residues, and then place it in a vacuum drying oven at 70 °C for 12 h to dry and remove water, thus obtaining the polymerizable ionic liquid [ATAC][TFSI]. Take 1.41 g of [N 4111 Cl to replace the ATAC solution, and through the same preparation process as above, the solvent ionic liquid [N 4111 [TFSI] can be obtained.

[0090] (2) Weigh 438.4 mg of [ATAC][TFSI] (1 mmol) and 297.3 mg of [N 4111 [TFSI] (0.75 mmol) in a glass bottle, add 1.0 μL of crosslinking agent PEGDA, 0.2 μL of silane coupling agent TMSPMA, and 2.0 μL of photoinitiator DEAP, and ultrasonicate for 20 min to fully mix each component. Then pour the precursor into a customized polytetrafluoroethylene mold. Under N2 protection, carry out ultraviolet polymerization for 600 s to obtain a gel-like transparent polyionic liquid film.

[0091] (3) Mix deionized water and absolute ethanol in a volume ratio of 1:1, add TMSPMA, and prepare a 2 wt% TMSPMA solution. Take 200 μL of the 2 wt% TMSPMA water / ethanol solution and drop it onto the surface of the ion gel network, and leave it at room temperature for 12 h. Then wash the modified ion gel network with absolute ethanol, store it in a lower humidity environment after complete drying.

[0092] (4) Weigh 720 mg of C6M and 29 mg of LC756 and dissolve them in 600 mg of dichloroethane solvent. Heat at 80 °C to completely dissolve the monomers. After cooling to room temperature, add 90.2 mg of 1,6 - hexanedithiol, 99.65 mg of TTMP, and 4 mg of Irg 1173. Add 180 mg of diluted n - hexylamine solution (dichloroethane:n - hexylamine = 50:1), stir the mixed solution at room temperature for 5 min to make it well - mixed, and then place it in a vacuum drying oven to remove bubbles. Then pour the precursor onto the ion gel network and leave it at room temperature in a fume hood for 24 h. Finally, irradiate it with ultraviolet light of 5 mW / cm 2 for 600 s for curing to obtain an ion - conductive cholesteric liquid crystal elastomer with an ion gel network as the lower layer and CLCE as the upper layer.

[0093] (5) Stack two iCLCEs with the same size to form a four - layer capacitive pressure sensor. The upper - layer CLCE provides structural color, and the middle - layer CLCE serves as a dielectric. The ion gels in the second and fourth layers are used as flexible conductive layers and are connected to wires. Observe the color and capacitance changes of the iCLCE capacitive sensor during the pressing process.

[0094] The structural formulas of the reactants used in this example are as follows:

[0095]

[0096] Figure 11 For (a) the color - change picture and (b) the reflection spectrum of the capacitive sensor during the pressing process, it can be seen that the iCLCE sensor has a sensitive color change during the pressing process, and its reflection wavelength gradually undergoes a blue - shift as the pressure increases.

[0097] Figure 12 For the relative capacitance change of the capacitive sensor during the pressing process, in the pressure range of 0 - 200 kPa, as the pressure increases, the thickness of the CLCE layer decreases, and the relative capacitance of the capacitive sensor linearly increases. Through calculation, the capacitance signal sensing sensitivity is 0.82 kPa -1 .

[0098] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A preparation method of an ion-conductive cholesteric liquid crystal elastomer, characterized in that, The preparation method includes the following steps: Step 1) Preparation of ionic liquid Dissolve the organic cation compound and the anion compound, stir, let it stand for layering, then take the transparent oily liquid, wash to remove residues, heat and dry to obtain a polymerizable ionic liquid; replace the organic cation compound, and through the same preparation process as above, obtain a solvent ionic liquid; Step 2) Preparation of ion gel Mix the polymerizable ionic liquid and the solvent ionic liquid prepared in Step 1) in a predetermined ratio, add a crosslinking agent, a silane coupling agent and a photoinitiator and mix evenly, pour it into a mold, and carry out ultraviolet polymerization under nitrogen protection to obtain a transparent ion gel; Step 3) Surface modification of ion gel Dropwise apply a silane coupling agent solution with a predetermined concentration on the surface of the ion gel prepared in Step 2), let it stand at room temperature, wash the surface of the ion gel, and store it in a low humidity environment condition after complete drying; Step 4) Preparation of iCLCE Using the ion gel obtained in Step 3) as the substrate, in-situ prepare iCLCE by the anisotropic evaporation method: dissolve the polymerizable liquid crystal monomer and the chiral agent in a solvent, heat to completely dissolve the polymerizable liquid crystal monomer, cool to room temperature, then add a chain extender, a crosslinking agent, a photoinitiator and a catalyst and mix evenly, vacuum dry and degas to obtain a precursor, pour the precursor on the ion gel surface-modified with the silane coupling agent prepared in Step 3), let it stand at room temperature, after the first-stage Michael addition is completed, carry out the second-stage free radical photopolymerization reaction to obtain iCLCE with an ion gel layer below and a CLCE layer above; The polymerizable liquid crystal monomer is selected from one or more of the compounds represented by formula (I), In formula (I), A and B each independently represent an aromatic ring or an alicyclic ring, and A and B may contain side groups, which are halogen, or cyano, or methyl; x and y are each 0 to 4; Z is an ester group, or an alkynyl group, or an alkyl group, or directly connected, or a nitrogen-nitrogen double bond, or an ether bond; R1 is an alkyl group containing 1 to 16 carbon atoms; R2 is an alkyl group containing 1 to 16 carbon atoms, or an acryloyloxy group containing 1 to 16 carbon atoms, or a siloxanyl group containing 1 to 16 atoms, or an ester group, or a cyano group, or a halogen, or an isothiocyanato group, or a nitro group.

2. The preparation method according to claim 1, wherein, The organic cation raw material for preparing the polymerizable ionic liquid in Step 1) is ATAC Cl or MATAC Cl, and the anion raw material is Li TFSI, Li BF4, or Li PF6; In step 1), the organic cation of the solvent ionic liquid is N 4111 Cl or N 4111 Br, and the anion raw materials for preparing the solvent ionic liquid are LiTFSI, LiBF4 or LiPF6.

3. The preparation method according to claim 1, characterized in that, In the raw materials for preparing the ion gel in Step 2), the polymerizable ionic liquid, the solvent ionic liquid, the crosslinking agent, the silane coupling agent, and the photoinitiator are in the following weight ratios respectively: In step 2), ultrasonic mixing is used for 20 to 40 minutes. The mold used is a polytetrafluoroethylene mold with a length of 35 to 50 mm, a width of 25 to 40 mm, and a depth of 2 to 5 mm. The light source for ultraviolet polymerization is a UV light source with a wavelength of 365 nm and a light intensity of 5 to 200 mW / cm 2 , and the polymerization time is 60 s to 1800 s.

4. The preparation method according to claim 1, characterized in that The preparation process of the silane coupling agent solution in Step 3) is: mix deionized water and absolute ethanol in a certain ratio, and add a silane coupling agent, wherein the ratio of deionized water to absolute ethanol is 1:1 to 1:0.5, and the concentration range of the silane coupling agent solution is 1.0 to 5.0 wt%; the dropwise application content of the silane coupling agent solution is 100 to 500 μL, and the ion gel surface is washed 5 to 10 times; The silane coupling agent used in Step 3) is TMSPMA, A-171 or A-172.

5. The preparation method according to claim 1, characterized in that, In step 4), the ratio of the total molar amount of the acryloyloxy groups of the polymerizable liquid crystal monomer and the chiral agent to the total molar amount of the mercapto groups of the chain extender and the crosslinking agent in the raw materials for preparing iCLCE is 1:1 to 11:10; the molar ratio of the crosslinking agent to the chain extender is 1:19 to 1:4; The boiling point of the solvent for dissolving the polymerizable liquid crystal monomer and the chiral agent does not exceed 130 °C, and the solvent is selected from one or more of toluene, dichloromethane, and dichloroethane; The chain extender is one or more of EDDET, 1,3-propanedithiol, and 1,6-hexanedithiol; The crosslinking agent is one or more of TTMP and PETMP; The catalyst for catalyzing the first-stage Michael addition reaction is selected from one or more of dipropylamine, triethylamine, and n-hexylamine; The photoinitiator for initiating the second-stage free radical photopolymerization reaction is selected from one or more of Irg 651, Irg 819, and Irg 1173; The reaction temperature of the first-stage polymerization reaction is 15°C to 35°C, and the reaction time is 18 to 36 h. The light source used in the second-stage photopolymerization reaction is a UV light source with a wavelength of 365 nm, and the light intensity is 5 to 200 mW / cm 2 , and the polymerization time is 60 s to 1800 s.

6. The preparation method according to claim 1, wherein The polymerizable liquid crystal monomer includes a mono-reactive functional liquid crystal monomer and / or a di-reactive functional liquid crystal monomer, and the phase transition temperature is 30 °C to 180 °C, and is selected from one or more of the following formulas: Among them, x and y are each 1 to 16, and A and B each independently represent hydrogen, halogen, alkyl, alkoxy, carboxyl, or cyano.

7. An ion-conductive cholesteric liquid crystal elastomer prepared by the method according to any one of claims 1-6.

8. Application of the ion-conductive cholesteric liquid crystal elastomer according to claim 7 in a photoelectric dual-signal response sensor, characterized in that, Its optical visualization and electrical signal response processes are as follows: 1) During stretching, bending, and pressing, the thickness of the iCLCE film in the observation direction, that is, perpendicular to its plane, decreases, and the pitch decreases. According to Bragg's reflection law λ = n×p×cosθ, where λ is the reflection wavelength, n is the average refractive index, P is the pitch, and θ is the angle of the incident light, its reflection wavelength undergoes a blue shift; 2) During stretching and bending, the length of the iCLCE increases in the ion conduction direction, the cross-sectional area decreases, the resistance increases, and the conductivity decreases; during pressing, the thickness of the intermediate layer CLCE decreases, and the sensor capacitance increases.

9. Application of the ion-conductive cholesteric liquid crystal elastomer according to claim 7 in a human motion monitoring and human-computer interaction system.

10. Application of the ion-conductive cholesteric liquid crystal elastomer according to claim 7 in artificial skin or intelligent robots.

11. A capacitive sensor, characterized in that, It is formed by stacking two ion-conductive cholesteric liquid crystal elastomers according to any one of claims 1-7 to form a four-layer structure. The four-layer structure is the first layer CLCE, the second layer ion gel, the third layer CLCE, and the fourth layer ion gel. The first layer CLCE provides structural color, the third layer CLCE serves as a dielectric, and the second layer ion gel and the fourth layer ion gel serve as flexible conductive layers and are connected to wires.

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