CN113667135B

CN113667135B - Preparation method of intrinsic carbon nanotube/liquid crystal elastomer and application of intrinsic carbon nanotube/liquid crystal elastomer in actuator

Info

Publication number: CN113667135B
Application number: CN202110958367.4A
Authority: CN
Inventors: 刘旭影; 张居中; 刘水任; 孙丹丹; 陈金周
Original assignee: Zhengzhou University
Current assignee: Zhengzhou University
Priority date: 2021-08-20
Filing date: 2021-08-20
Publication date: 2022-06-17
Anticipated expiration: 2041-08-20
Also published as: CN113667135A

Abstract

The invention belongs to the technical field of intelligent materials, and discloses a preparation method of an intrinsic carbon nanotube/liquid crystal elastomer and application of the intrinsic carbon nanotube/liquid crystal elastomer in an actuator. The carbon nano tube introduces a modification group through functional modification, so that an intrinsic carbon nano tube/liquid crystal elastomer network is formed with the liquid crystal element, the cross-linking agent and the spacer under the conditions of thermal polymerization and photopolymerization. The average tensile strength of the intrinsic carbon nanotube/liquid crystal elastomer prepared by the method can reach 13.87MPa, the intrinsic carbon nanotube/liquid crystal elastomer is improved by 4.2 times compared with a pure liquid crystal elastomer, and the infrared actuating stress and the ultraviolet actuating stress respectively reach 1.66MPa and 1.28 MPa. By preparing the multilayer actuator of the intrinsic carbon nano tube/liquid crystal elastomer and the snake-shaped actuator, multiple responses of the actuator to stimuli such as temperature, light and the like are realized. In addition, the method provides a new idea for designing and preparing novel high-performance intelligent materials, and is expected to be applied to bionic devices such as artificial muscles and intelligent grippers.

Description

Preparation method of intrinsic carbon nanotube/liquid crystal elastomer and application of intrinsic carbon nanotube/liquid crystal elastomer in actuator

Technical Field

The invention belongs to the technical field of intelligent materials, and particularly relates to a preparation method of an intrinsic carbon nanotube/liquid crystal elastomer and application of the intrinsic carbon nanotube/liquid crystal elastomer in an actuator.

Background

The actuator is a mechanism which directly or indirectly controls a mechanical structure to deform, move or prevent deformation under external field stimulation such as electricity, heat, light and the like. Smart materials for constructing actuators are required to have both responsiveness and drivability characteristics. As a new intelligent polymer material, the Liquid Crystal Elastomer (LCE) can generate reversible macroscopic shape change by changing the liquid crystal order in the polymer under the external stimulation of heat, light, chemical substances, electric or magnetic fields and the like, so that the LCE has wide application prospect in a plurality of intelligent fields such as artificial muscles, flexible robots, intelligent surfaces and the like. However, the liquid crystal elastomer prepared by the conventional method has the problems of poor mechanical strength, low actuation stress, single response mode (mainly thermal response) and the like, so that the application of the liquid crystal elastomer is limited.

The carbon nanotube has high mechanical strength (1TPa) and high thermal conductivity (up to 6000 W.m)^-1·K^-1) And good light absorption are widely used in the research of liquid crystal elastomers, and an actuator constructed therewith can generate a large output force. Research shows that the carbon nano tube can efficiently absorb near infrared laser. The near-infrared response has been widely used in stimulation response due to its strong penetration, remote control, local drive and innocuity. Therefore, the carbon nano tube can convert the light energy into the heat energy by utilizing the near-infrared laser to form a molecular heater, and further trigger the liquid crystal elastomer composite material to generate mechanical response. However, the carbon nanotubes are easily aggregated into bundles due to van der waals force, resulting in inefficient transfer of load between the carbon nanotubes or between the carbon nanotubes and the liquid crystal elastomer; but also results in inefficient conversion of light to heat. In addition, the carbon nanotubes have a higher thermal conductivity along the long axis direction, and if the carbon nanotubes are induced to be oriented in the matrix, a small amount of the carbon nanotubes can play a greater role. However, since the aspect ratio (L/D) of carbon nanotubes is relatively large, difficulty in orientation is another fundamental problem. The existence of these problems has greatly limited the application of the excellent properties of carbon nanotubes in liquid crystal elastomers.

Disclosure of Invention

The invention aims to provide a preparation method of an intrinsic carbon nanotube/liquid crystal elastomer, which effectively solves the problems of dispersion and orientation of carbon nanotubes in a liquid crystal elastomer matrix so as to realize excellent tensile strength, actuation stress and multiple response characteristics in the application of an actuator.

Based on the above purpose, the technical scheme adopted by the invention is as follows:

the invention provides a preparation method of an intrinsic carbon nanotube/liquid crystal elastomer, which comprises the following steps:

(1) performing functional modification on the carbon nano tube by using a modifying group substance to obtain a functional carbon nano tube grafted with a modifying group;

(2) adding a liquid crystal element and a photoinitiator into a solvent, and dissolving to obtain a solution;

(3) adding a cross-linking agent, a spacer, a catalyst and a functionalized carbon nanotube into the solution prepared in the step (2), and uniformly stirring to obtain a dispersion liquid a;

(4) casting the dispersion liquid a into a mould for polymerization reaction to obtain a multi-domain intrinsic carbon nanotube/liquid crystal elastomer;

(5) and (3) performing uniaxial stretching treatment on the multi-domain intrinsic carbon nanotube/liquid crystal elastomer, curing the multi-domain intrinsic carbon nanotube/liquid crystal elastomer under an ultraviolet lamp, and removing the stretching load after curing to obtain the single-domain intrinsic carbon nanotube/liquid crystal elastomer.

Preferably, the carbon nanotube is at least one of a hydroxylated carbon nanotube, an aminated carbon nanotube and a carboxylated carbon nanotube.

More preferably, the carbon nanotubes are hydroxylated carbon nanotubes.

More preferably, the functionalized carbon nanotubes in step (3) are added into a solvent, and after a dispersion liquid is obtained by ultrasonic treatment, the dispersion liquid is added into the solution prepared in step (2).

More preferably, the polymerization reaction temperature in the step (4) is 50-100 ℃, and the polymerization reaction time is 12-36 h.

Preferably, the modifying group substance is at least one of 10-undecenoyl chloride, 10-undecenoyl alcohol, acryloyl chloride, 4-pentenoyl chloride, 10-undecenoyl acid and 11-dodecenoic acid.

More preferably, the modifying group species is 10-undecenoyl chloride and acryloyl chloride.

Preferably, the specific operation of performing functional modification on the carbon nanotube by using the modifying group substance in the step (1) is as follows:

1) adding the dried carbon nano tube into a solvent under the atmosphere of protective gas, and performing ultrasonic treatment and uniform stirring to obtain a carbon nano tube dispersion liquid;

2) slowly dripping a catalyst into the carbon nano tube dispersion liquid in a protective gas atmosphere, and uniformly stirring to obtain a mixed liquid;

3) dropwise adding a modifying group substance into the mixed solution prepared in the step 2) under the atmosphere of protective gas, stirring and reacting for 2-4 h, and then continuously reacting for 1-2 h at room temperature to obtain a reaction mixture;

4) and centrifuging and filtering the reaction mixture, collecting filtrate, and washing and drying the filtrate to obtain the functionalized carbon nanotube.

Preferably, the molar ratio of the active group, the modifying group substance and the catalyst of the carbon nanotube in the process of functionally modifying the carbon nanotube is 1: 2-10, wherein the active group of the hydroxylated carbon nanotube is hydroxyl, the active group of the carboxylated carbon nanotube is carboxyl, and the active group of the aminated carbon nanotube is amino.

More preferably, the molar ratio of the hydroxyl group of the hydroxylated carbon nanotube, the modifying group substance and the catalyst in the process of performing functional modification on the hydroxylated carbon nanotube is 1: 10.

More preferably, in the process of performing functional modification on the hydroxylated carbon nanotube, the steps 1) to 3) are performed under ice-water bath conditions.

More preferably, the drying process is performed under vacuum condition during the process of performing the functional modification on the carbon nanotubes.

Preferably, the liquid crystal elements are one or two of RM82 and RM 257.

More preferably, the mesogen is RM 82.

Preferably, the spacer is at least one of 1, 2-ethanedithiol, 1, 3-propanedithiol, 1, 5-pentanedithiol, 1, 6-hexanedithiol, 1, 8-octanedithiol, 1, 9-nonanedithiol, 1, 10-decanedithiol, 3, 6-dioxa-1, 8-octanedithiol.

More preferably, the spacer is 1, 10-decanedithiol.

Preferably, the crosslinking agent is at least one of pentaerythritol tetrakis (3-mercaptopropionate), pentaerythritol tetrakis (mercaptoacetate), trimethylolpropane tris (3-mercaptopropionate), dipentaerythritol hexa (3-mercaptopropionate).

More preferably, the crosslinker is pentaerythritol tetrakis (3-mercaptopropionate).

Preferably, in the method for preparing the intrinsic carbon nanotube/liquid crystal elastomer, the mass ratio of the mesogen to the cross-linking agent to the spacer is (50-80) to (5-10) to (10-15.5), the mass of the functionalized carbon nanotube accounts for 0.05-5% of the sum of the mass of the mesogen, the cross-linking agent and the spacer, the mass of the catalyst accounts for 0.1-0.57% of the sum of the mass of the mesogen, the cross-linking agent and the spacer, and the mass of the photoinitiator accounts for 2-8% of the sum of the mass of the mesogen, the cross-linking agent and the spacer.

Preferably, the carbon nanotube is one or two of a single-walled carbon nanotube and a multi-walled carbon nanotube.

More preferably, the carbon nanotubes are multi-walled carbon nanotubes.

Preferably, the diameter of the carbon nano tube is 0.5-10 nm, and the length of the carbon nano tube is 2-50 μm.

More preferably, the solvent is at least one of toluene, dichloromethane, chloroform, and N, N-dimethylformamide.

More preferably, the photoinitiator is 2, 2-dimethoxy-phenylacetophenone.

More preferably, the catalyst in the carbon nanotube modification process is triethylamine.

More preferably, the catalyst in the preparation method of the intrinsic carbon nanotube/liquid crystal elastomer is di-n-propylamine.

The invention provides an intrinsic carbon nano tube/liquid crystal elastomer product prepared by the preparation method in a second aspect.

The invention provides the application of the intrinsic carbon nano tube/liquid crystal elastomer product prepared by the preparation method in an actuator, preferably an infrared laser, an ultraviolet laser and/or a thermal response actuator.

The invention provides a method for preparing an intrinsic carbon nanotube/liquid crystal elastomer actuator, which comprises the following steps: providing the single-domain intrinsic carbon nanotube/liquid crystal elastomer, and cutting the single-domain intrinsic carbon nanotube/liquid crystal elastomer into sample strips with certain sizes along the stretching direction; and (3) bonding the prepared splines together in a layer-by-layer stacking manner by using an adhesive, mutually pressing the contact parts, and carrying out polymerization reaction to prepare the multilayer actuator.

More preferably, the binder in the above method for manufacturing a multilayer actuator is the dispersion a or the dispersion a containing no functionalized carbon nanotubes in step (3) in the above method for manufacturing an intrinsic type carbon nanotube/liquid crystal elastomer of the first aspect.

More preferably, in the method for manufacturing the multilayer actuator, the polymerization temperature is 50-80 ℃ and the polymerization time is 6 hours.

The fifth aspect of the present invention provides another method for manufacturing an intrinsic type carbon nanotube/liquid crystal elastomer actuator, comprising the steps of: providing the single-domain intrinsic carbon nanotube/liquid crystal elastomer, winding the single-domain intrinsic carbon nanotube/liquid crystal elastomer around a plurality of parallel tubes in a bending way, and fixing the shape under ultraviolet light to prepare the snake-shaped actuator.

More preferably, the wavelength of the ultraviolet light in the above method for manufacturing the serpentine actuator is 365 nm.

More preferably, the fixing time in the preparation method of the snake-shaped actuator is 10-15 min.

Compared with the prior art, the invention has the following beneficial effects:

(1) the invention utilizes the carbon-carbon double bond at the tail end of the functionalized carbon nano tube modification group to be bonded with the liquid crystal element through the mercapto group of the cross-linking agent and the spacer in a chemical grafting mode to form a liquid crystal elastomer network, improves the dispersion and orientation of the carbon nano tube in the matrix, completes the cross-linking between the double bonds under the initiation of the subsequent photoinitiator, fixes the orientation of the liquid crystal element to form the single-domain intrinsic carbon nano tube/liquid crystal elastomer, and finally realizes the preparation of the intrinsic carbon nano tube/liquid crystal elastomer actuator with excellent mechanical property and multiple response functions through further processing. The method improves the dispersion of the carbon nano tube in the liquid crystal elastomer matrix through the covalent grafting and the pi-pi interaction, and inhibits the phase separation between the carbon nano tube and the liquid crystal elastomer matrix; and after the carbon nano tubes are added, the gel content of the liquid crystal elastomer is obviously improved because the carbon nano tubes play a role of nucleation in the liquid crystal elastomer matrix. These all provide new thinking for designing and preparing novel high-performance intelligent material, are expected to be applied to bionical devices such as artificial muscle, intelligent tongs.

(2) The invention adopts at least one of hydroxylated carbon nano-tubes, aminated carbon nano-tubes and carboxylated carbon nano-tubes. The carbon nano tube with the surface provided with hydroxyl, amino and carboxyl functional groups is used to react with a modifying group substance with carbonyl chloride, carboxyl and other functional groups respectively through a catalyst, so as to obtain the functionalized carbon nano tube with the surface provided with carbon-carbon double bond modifying groups. And the carbon-carbon double bond is positioned at the tail end of the modification group, so that a reaction active point is provided for the next chemical grafting reaction.

(3) The spacer and the chain end of the cross-linking agent both contain sulfydryl, so that the Michael addition reaction of mercaptan and acrylate with carbon-carbon double bonds in the liquid crystal element and the functional carbon nanotube can be conveniently carried out. After the carbon nano tube/liquid crystal elastomer subjected to stretching orientation is excited by ultraviolet light, the photoinitiator generates free radicals to initiate free radical addition reaction so as to complete the crosslinking reaction between carbon-carbon double bonds, and thus the single-domain carbon nano tube/liquid crystal elastomer is formed. Because the formed chemical bond is difficult to break and the free radical addition reaction is irreversible, the connection of the intrinsic carbon nanotube/liquid crystal elastomer formed by the method is difficult to be damaged due to the change of the external environment, and the formed structure is firmer, so that the performance of the material can be optimized and the application reliability can be improved.

(4) After the functionalized carbon nanotubes are covalently grafted in the liquid crystal elastomer matrix, in one embodiment, a "strip-shaped structure" with a diameter of about 600nm and good orientation is formed in the matrix, which shows that the functionalized carbon nanotubes prepared by the method have good compatibility with the liquid crystal elastomer matrix.

(5) The multi-domain carbon nanotube/liquid crystal elastomer prepared by the invention is an unoriented polymer and shows isotropy, and the internal structure of the multi-domain carbon nanotube/liquid crystal elastomer is preferentially arranged along a specific direction for orientation through uniaxial stretching treatment, so that the mono-domain carbon nanotube/liquid crystal elastomer is obtained. The single-domain carbon nanotube/liquid crystal elastomer is anisotropic, and the application range of the anisotropic single-domain carbon nanotube/liquid crystal elastomer is wider.

(6) The intrinsic carbon nanotube/liquid crystal elastomer and the actuator thereof prepared by the invention have excellent mechanical property and optical actuation property. In one embodiment, the average tensile strength of the intrinsic carbon nanotube/liquid crystal elastomer is increased by 4.2 times compared with that of the pure liquid crystal elastomer; the infrared laser actuating stress and the ultraviolet laser actuating stress respectively reach 1.66MPa and 1.28 MPa. In one embodiment, 36mg of the intrinsic carbon nanotube/liquid crystal elastomer can lift up a weight of 210g under irradiation of infrared laser.

(7) The intrinsic carbon nanotube/liquid crystal elastomer and the actuator thereof prepared by the invention have multiple response functions and keep higher stability. The intrinsic carbon nanotube/liquid crystal elastomer can quickly reach the phase transition temperature under the irradiation of the same near-infrared laser density, and can keep stable in the temperature rising and falling process. In one embodiment, the liquid crystal elastomer containing functionalized carbon nanotubes (MWNT-AC) reaches the phase transition temperature more rapidly under the same infrared laser density irradiation, wherein the intrinsic carbon nanotube/liquid crystal elastomer has higher photothermal conversion efficiency. In one embodiment, the multilayer intrinsic carbon nanotube/liquid crystal elastomer actuator can be reversibly deformed under the stimulation of temperature change, near infrared laser and ultraviolet laser, and high stability is maintained.

(8) According to the serpentine intrinsic carbon nanotube/liquid crystal elastomer actuator prepared by the invention, different parts of the actuator are stretched and bent, and liquid crystal cells are endowed with different orientation directions, so that when near-infrared laser is irradiated to different positions of the actuator, deformation of different degrees can occur. In one embodiment, the snake-shaped actuator realizes actions of straight running, turning and the like under the control of the infrared laser point.

Drawings

FIG. 1 is a schematic diagram of the functional modification reaction principle of a hydroxylated carbon nanotube;

FIG. 2 is a schematic diagram of the reaction principle of intrinsic carbon nanotube/liquid crystal elastomer, wherein a is the raw material required by the preparation process, and b is the diagram of the prepared multi-domain intrinsic carbon nanotube/liquid crystal elastomer;

FIG. 3 is an infrared spectrum of an intrinsic type carbon nanotube/liquid crystal elastomer, wherein a is an infrared spectrum of a raw material for synthesizing LCE and LCE, and b is an infrared spectrum of samples prepared in examples 1 to 2 and comparative examples 1 to 5;

FIG. 4 is a picture of a filter paper obtained by Soxhlet extraction of a sample and a picture obtained by swelling the sample in a chloroform solvent, wherein a is the filter paper obtained by Soxhlet extraction of MWNT-PC/LCE and MWNT-UAC/LCE (left) and MWNT-AC/LCE and MWNT-UEC/LCE (right), and b-d are the pictures obtained by swelling the MWNT-AC/LCE, MWNT-OH/LCE and MWNT-AC/LCE in a chloroform solvent, respectively;

FIG. 5 is a surface topography of a tensile section of a sample, wherein a is an LCE sample, b is an MWNT-AC/LCE sample, c is an MWNT-UEC/LCE sample, d is an MWNT-UAC/LCE sample, e is a partial enlargement of b, f is a partial enlargement of c, and g is an MWNT-OH/LCE sample;

FIG. 6 is a surface topography of a cross-section of MWNT-AC/LCE, where a is SEM, b is a close-up view of a, c is TEM, and d is AFM;

FIG. 7 is a 120kV TEM image of MWNT-AC/LCE, wherein a-f are the distribution of carbon nanotubes at different positions in the MWNT-AC/LCE matrix;

FIG. 8 is a photograph of the polarization of a sample in a single domain state, wherein a and c are photographs of LCE and MWNT-AC/LCE under polarization, respectively, and b and d are photographs of LCE and MWNT-AC/LCE under polarization rotated by 45 °, respectively;

FIG. 9 is a plot of the stress-strain curve and the average tensile strength bar graph for the sample, where a and b are the stress-strain curves for the sample in the transverse and longitudinal directions, respectively, along the direction of stretching; c and d are bar graphs of the average tensile strength of the sample in the transverse and longitudinal directions, respectively, of the stretching direction;

FIG. 10 is a plot of laser density versus actuation stress for a sample, where a is the plot of infrared laser density versus actuation stress for the sample, and b is the plot of infrared laser density at 344mW/cm for the sample, and the actuation stability at a fixed laser density²C is the curve of the ultraviolet laser density and the actuating stress of the sample, d is the curve of the ultraviolet laser density of the sample at 568 mW/cm²Lower actuation stability curve;

FIG. 11 is a TG curve and a DTG curve of a sample, wherein a is a TG curve and b is a DTG curve;

FIG. 12 is a UV-VIS-NIR spectrum of all monomers in MWNT-AC/LCE and LCE;

FIG. 13 is a graph of two deformation profiles exhibited by a sample during cooling and a graph of the change in length of the sample measured during alternating heating and cooling, wherein a is a graph of two deformation profiles exhibited by MWNT-AC/LCE during cooling; b-d are respectively length variation graphs of LCE, MWNT-AC/LCE and MWNT-UEC/LCE measured in the process of alternating heating and cooling;

FIG. 14 is a plot of fixed infrared laser illumination power density versus sample surface temperature and corresponding infrared images, where a is at 318mW/cm²B is 604mW/cm at the infrared laser illumination power density of²C is 870mW/cm under the infrared laser illumination power density²Under the infrared laser illumination power density;

FIG. 15 is a graph of the deformation of the actuator under control of the laser spot and the MWNT-AC/LCE versus the sample surface temperature under fixed infrared laser alternating switch illumination, where a and b are the shape deformations of the multilayer LCE actuator and multilayer MWNT-AC/LCE actuator under control of the laser spot, respectively, and c is the MWNT-AC/LCE at an infrared laser power density of 604mW/cm²A graph of the relationship between the temperature and the surface temperature of the sample under the irradiation of the alternate switch, wherein a ruler is 1 cm;

FIG. 16 is a key diagram of the fabrication of a serpentine MWNT-AC/LCE actuator and the straight and turning process of the serpentine actuator under the control of the laser spot.

Detailed Description

Example 1

The embodiment of the invention provides a preparation method of an intrinsic carbon nanotube/liquid crystal elastomer, which comprises the following steps:

1. functionalization process of carbon nanotubes

1) 200mg of 0.656mmol of hydroxylated carbon nanotube (MWNT-OH) is weighed and placed in a vacuum drying oven, and dried for 12 hours at the temperature of 60 ℃ under the vacuum condition for standby. And placing the dried hydroxylated carbon nano tube into a two-mouth reaction bottle to form a sealing system. 40mL of methylene chloride was injected into the reaction flask to obtain a suspension, and nitrogen was purged. And placing the suspension in an ice-water bath environment for ultrasonic treatment for 60min to obtain uniform carbon nanotube dispersion, and then placing the reaction flask in a Dewar flask filled with ice-water mixture to cool the carbon nanotube dispersion to 0 ℃.

2) Triethylamine (0.93mL, 6.56mmol) was slowly added dropwise to the uniformly stirred carbon nanotube dispersion under ice-water bath conditions to obtain a mixed solution.

3) Acryloyl chloride (0.54mL, 6.56mmol) was slowly added dropwise to the mixture prepared in step 2). The mixture was stirred at 0 ℃ for 4 hours under nitrogen, followed by 2 hours at room temperature.

4) The reaction mixture was centrifuged at 3000rpm for 2min to remove the solvent. To remove triethylamine hydrochloride and unreacted monomers, the collected black solid powder was filtered by suction through a 0.45 μm pore size membrane and washed thoroughly with dichloromethane and absolute ethanol. And finally, placing the black solid powder in a vacuum oven to be dried for 24 hours in vacuum at the temperature of 80 ℃ to obtain the functionalized carbon nano tube, and marking as MWNT-AC. The functional modification reaction principle of the hydroxylated carbon nanotube is shown in figure 1.

2. Preparation of intrinsic carbon nanotube/liquid crystal elastomer

The intrinsic carbon nanotube/liquid crystal elastomer is prepared by combining a one-pot method with two-step crosslinking and uniaxial stretching technologies, and the intrinsic carbon nanotube/liquid crystal elastomer is prepared from the following raw materials: 1, 4-bis- [4- (6-acryloyloxyethoxy) benzoyloxy ] -2-methylbenzene (RM82) is a liquid crystal element, pentaerythritol tetrakis (3-mercaptopropionate) (PETMP) is a cross-linking agent, 1, 10-Decanedithiol (DT) is a spacer, a functionalized carbon nanotube (MWNT-AC), di-n-propylamine (DPA) is a catalyst, 2, 2-dimethoxy-phenylacetophenone (DMPA) is a photoinitiator, and toluene is a solvent. The specific dosage ratio of the raw materials is shown in table 1:

TABLE 1 raw material ratio of intrinsic carbon nanotube/liquid crystal elastomer

The preparation method comprises the following steps:

(1) 1g of RM82 and 0.0645g of DMPA were weighed out and dissolved in a small amount of toluene solvent and heated at 80 ℃ to form a homogeneous solution.

(2) 0.0872g of PETMP, 0.3107g of DT and 0.0013g of MWNT-AC were weighed out and added to the solution prepared in step (1), and 0.0020784g of DPA was added and shaken on a shaker (SCILOGEX MX-S) for 1 hour to obtain a uniform dispersion a.

(3) Casting the dispersion a into a Polytetrafluoroethylene (PTFE) mold, and putting the mold into a vacuum oven to react for 12 hours at 60 ℃ so as to complete the Michael addition reaction of thiol and acrylate. Then, the film is placed for 24 hours under the vacuum condition at the temperature of 80 ℃, the solvent is evaporated, and bubbles are removed, so that the multi-domain intrinsic carbon nano tube/liquid crystal elastomer film is obtained.

(4) And when the temperature is cooled to room temperature, the multi-domain carbon nanotube/liquid crystal elastomer film is stretched uniaxially and placed under 365nm UV light for 15min to complete the acrylate-acrylate crosslinking reaction, and at the moment, the carbon nanotube/liquid crystal elastomer is converted into a single-domain state from a multi-domain state, which is marked as MWNT-AC/LCE. The reaction principle of the intrinsic type carbon nanotube/liquid crystal elastomer prepared in example 1 is shown in fig. 2.

Example 2

The preparation method of the intrinsic carbon nanotube/liquid crystal elastomer is basically the same as that of the embodiment 1, and the difference is that: the modifying group substance is 10-undecylenoyl chloride, the obtained functionalized carbon nano tube is marked as MWNT-UEC, and the obtained single-domain carbon nano tube/liquid crystal elastomer is marked as MWNT-UEC/LCE.

Example 3

The preparation method of the intrinsic carbon nanotube/liquid crystal elastomer is basically the same as that of the embodiment 1, and the difference is that: the raw material ratios for preparing the intrinsic carbon nanotube/liquid crystal elastomer are different, and are specifically shown in table 3.

Table 3 raw material compounding ratio of sample prepared in example 3

Example 4

The preparation method of the intrinsic carbon nanotube/liquid crystal elastomer is basically the same as that of the embodiment 1, and the difference is that: the specific ratios of the ingredients for preparing the intrinsic carbon nanotube/liquid crystal elastomer are shown in table 4.

Table 4 raw material ratios of samples prepared in example 4

Example 5

A preparation method of an intrinsic carbon nanotube/liquid crystal elastomer actuator comprises the following steps:

the intrinsic type carbon nanotube/liquid crystal elastomer sample prepared in example 1 was cut into a sample bar having a length of about 9mm and a width of about 5mm in a stretching direction; 10 pieces of the sample were bonded together in a layer-by-layer stacked manner using an adhesive, and then thermally polymerized in a vacuum oven at 60 ℃ for 6 hours to prepare a multilayer actuator. Wherein the binder is the dispersion a described in step (2) of example 1 or the dispersion a without MWNT-AC.

Example 6

A method for preparing an intrinsic carbon nanotube/liquid crystal elastomer actuator comprises the following steps:

the intrinsic type carbon nanotube/liquid crystal elastomer sample prepared in example 1 was wound around 4 parallel tubes in a bending manner and fixed in shape for 15min under 365nm ultraviolet light to prepare a serpentine actuator.

Example 7

The preparation method of the intrinsic carbon nanotube/liquid crystal elastomer actuator is basically the same as that of example 5, except that: the sample used was the intrinsic carbon nanotube/liquid crystal elastomer sample prepared in example 2; the binder is either dispersion a described in step (2) of example 2 or dispersion a without MWNT-UEC.

Example 8

The preparation method of the intrinsic carbon nanotube/liquid crystal elastomer actuator is basically the same as that of example 6, except that: the sample used was the intrinsic carbon nanotube/liquid crystal elastomer sample prepared in example 2.

Example 9

The preparation method of the intrinsic carbon nanotube/liquid crystal elastomer actuator is basically the same as that of example 5, except that: the sample used was the intrinsic carbon nanotube/liquid crystal elastomer sample prepared in example 3; the binder was either dispersion a described in step (2) of example 3 or dispersion a without MWNT-AC.

Example 10

The preparation method of the intrinsic carbon nanotube/liquid crystal elastomer actuator is basically the same as that of example 5, except that: the sample used was the intrinsic carbon nanotube/liquid crystal elastomer sample prepared in example 4; the binder was the dispersion a described in step (2) of example 4 or the dispersion a without MWNT-AC.

Example 11

The preparation method of the intrinsic carbon nanotube/liquid crystal elastomer actuator is basically the same as that of example 6, except that: the sample used was the intrinsic carbon nanotube/liquid crystal elastomer sample prepared in example 4.

Comparative example 1

The preparation method of the carbon nanotube/liquid crystal elastomer is basically the same as that of the embodiment 1, and the difference is that: the modifying group substance is propionyl chloride, the obtained functionalized carbon nanotube is marked as MWNT-PC, and the obtained single-domain carbon nanotube/liquid crystal elastomer is marked as MWNT-PC/LCE.

Comparative example 2

The preparation method of the carbon nanotube/liquid crystal elastomer is basically the same as that of the embodiment 1, and the difference is that: the modifying group substance is undecanoyl chloride, the obtained functionalized carbon nanotube is marked as MWNT-UAC, and the obtained single-domain carbon nanotube/liquid crystal elastomer is marked as MWNT-UAC/LCE.

Comparative example 3

The preparation method of the carbon nanotube/liquid crystal elastomer is basically the same as that of the embodiment 1, and the difference is that: and (2) modifying the hydroxylated carbon nanotube (MWNT-OH) without adopting a modifying group substance, directly adding the hydroxylated carbon nanotube into the solution prepared in the step (1) to prepare the carbon nanotube/liquid crystal elastomer, and marking the obtained single-domain carbon nanotube/liquid crystal elastomer as MWNT-OH/LCE.

Comparative example 4

The preparation method of the carbon nanotube/liquid crystal elastomer is basically the same as that of the embodiment 1, and the difference is that: and (2) preparing the carbon nanotube/liquid crystal elastomer by adopting a carbon nanotube (MWNT), namely directly adding the carbon nanotube into the solution prepared in the step (1) to prepare the carbon nanotube/liquid crystal elastomer, and marking the obtained single-domain carbon nanotube/liquid crystal elastomer as MWNT/LCE.

Comparative example 5

The preparation method of the liquid crystal elastomer is basically the same as that of the example 1, except that: the monodomain liquid crystalline elastomer was prepared directly as described in step 2 of example 1, with no carbon nanotubes added in step (2), and the monodomain liquid crystalline elastomer obtained was designated LCE.

Comparative example 6

A liquid crystal elastomer actuator was produced in substantially the same manner as in example 5 except that: the sample used was the liquid crystal elastomer sample prepared in comparative example 5; the binder was the dispersion a described in step (2) of comparative example 5.

To investigate the properties of the intrinsic carbon nanotubes/liquid crystal elastomers prepared from hydroxylated carbon nanotubes, the inventors performed the following performance tests on the samples prepared in examples 1-2 and comparative examples 1-5:

performance test experiments:

1. characterization and analysis of intrinsic carbon nanotube/liquid crystal elastomer

(1) Infrared spectroscopic analysis of intrinsic carbon nanotube/liquid crystal elastomers

1) Experimental methods

The structures of the liquid crystal elastomer sample strips prepared in examples 1 to 2 and comparative examples 1 to 5 were examined using an attenuated total reflection mode of a fourier transform infrared spectrometer. The liquid crystal elastomer sample is cut into 10mm × 5mm samples, and dried in a vacuum oven at 60 deg.C for 24h for use. Wiping the detector with absolute ethanol, drying, and placing the sample on the detector of an infrared spectrometer at 4000 cm^-1To 500cm^-1The sample and its raw material were scanned 16 times over the range. The results are shown in FIG. 3.

2) Results of the experiment

In FIG. 3, a is the IR spectrum results for the synthesized LCE. In the raw material, the wave number is 2572cm^-1The peak of (2) is attributed to the stretching vibration peak of mercapto group of PETMP and DT, and the wave number is 1636cm^-1The peak at (b) corresponds to the peak of stretching vibration of the carbon-carbon double bond of RM 82. After the first crosslinking, the infrared spectrum of the multi-domain LCE shows that the stretching vibration peak of the sulfydryl disappears, and the stretching vibration peak of the carbon-carbon double bond weakens, and moves to a low wave number region (1636 cm)^-1→1625cm^-1). Indicating that the carbon-carbon double bond undergoes a thiol-ene click reaction with the thiol group during the heating phase and stops reacting when all thiol groups are consumed, leaving an excess of acrylate groups. The multi-domain LCE completes the polymerization reaction in the second stage under the irradiation of ultraviolet light after being stretched uniaxially, and the disappearance of the stretching vibration peak of the carbon-carbon double bond can be seen from the infrared spectrogram, which shows that the polymerization reaction of acrylic ester and acrylic ester occurs in the photopolymerization stage, and the liquid crystal elastomer is successfully synthesized after thermal polymerization and photopolymerization. In the process, DT and PETMP generate sulfydryl, and then under the action of the catalyst, the carbon-carbon double bond of MWNT-AC, MWNT-UEC or RM82 is attacked to form alkyl. The hydrogen atom on the thiol is transferred to the alkyl group to form another mercapto group, which proceeds toThe process of chain transfer, and finally the chain termination by free radical coupling, results in a lightly crosslinked liquid crystalline elastomer.

In FIG. 3, b is the IR spectra of examples 1 to 2 and comparative examples 1 to 5. As can be seen from the figure, the introduction of the functionalized carbon nanotubes has little effect on the infrared spectrum of the liquid crystal elastomer because the content of the carbon nanotubes is relatively low, and the property of the carbon nanotubes as the nano material is reflected.

To further verify whether the carbon-carbon double bonds on the functionalized carbon nanotubes participate in the click chemistry reaction, the prepared MWNT-AC/LCE, MWNT-UEC/LCE, MWNT-PC/LCE, MWNT-UAC/LCE, MWNT-OH/LCE and MWNT/LCE were extracted with chloroform solvent, respectively, to determine whether the functionalized carbon nanotubes MWNT-AC and MWNT-UEC are connected to the polymer network. The results are shown in FIG. 4.

As shown in a in FIG. 4, there are traces of the mixture of carbon nanotubes and polymer on the filter paper after Soxhlet extraction of MWNT-PC/LCE, MWNT-UAC/LCE, MWNT-OH/LCE and MWNT/LCE, while there is no such phenomenon after Soxhlet extraction of MWNT-AC/LCE and MWNT-UEC/LCE, indicating that the chemically grafted MWNT-AC and MWNT-UEC are actually involved in the polymerization reaction.

In FIG. 4, b to d are photographs showing samples of LCE, MWNT-OH/LCE, MWNT-AC/LCE after swelling in chloroform solvent, respectively. After the sample is swelled by chloroform, a plurality of aggregated carbon nanotubes in MWNT-OH/LCE can be seen, MWNT-AC/LCE is relatively uniform, and no obvious aggregation is found, which shows that Van der Waals force between the carbon nanotubes is effectively weakened through covalent grafting between the carbon nanotubes and liquid crystal small molecules, and an effective way is provided for improving the dispersibility of the carbon nanotubes.

(2) Morphology analysis of intrinsic carbon nanotube/liquid crystal elastomer

1) Experimental methods

Scanning electron microscopy, double-spherical-aberration-corrected analytical field emission transmission electron microscopy and atomic force microscopy were used to examine the morphology of the samples prepared in examples 1-2 and comparative examples 2, 3, 5 and the compatibility between the carbon nanotubes and the liquid crystalline elastomer matrix.

A cross-sectional sample of a liquid crystal elastomer for a scanning electron microscope is prepared mainly by four ways: (1) stretch breaking; (2) placing the liquid crystal elastomer sample strip in liquid nitrogen for freezing and quenching; (3) the liquid crystal elastomer sample was embedded with an epoxy resin, and after drying for one week at normal temperature, the liquid crystal elastomer film was cut into a sample having a thickness of 1 μm on a freezing microtome. The epoxy resin is prepared by mixing 4.9mL of SPI-PON812, 1.65mL of DDSA, 3.45mL of NMA and 0.15-0.2 mL of DMP-30 at normal temperature. (4) The liquid crystalline elastomer bars were cooled to below the glass transition temperature (-80 ℃) on a refrigerated microtome and cut to a thickness of 1 μm. The sectional sample was a sample obtained by cooling a liquid crystal elastomer sample on a cryomicrotome to a temperature below the glass transition temperature (-80 ℃ C.) and cutting the sample into a thickness of 1 μm. And plating a layer of gold film on the prepared sample on a vacuum coating instrument, and finally observing the appearance of the sample by using a scanning electron microscope under a vacuum condition, wherein the accelerating voltage is 5 kV. The sample for the field emission transmission electron microscope of the double spherical aberration correction analysis type was prepared by cooling a sample of the liquid crystal elastomer on a cryomicrotome to below the glass transition temperature (-80 ℃) and cutting it into a sample having a thickness of 40nm, and then testing it at an accelerating voltage of 300 kV. The samples for atomic force microscopy were prepared by cooling liquid crystalline elastomer bars below the glass transition temperature (-80 ℃). The surface is then cut into flat surfaces. And finally, observing the appearance of the sample on an atomic force microscope. The results are shown in FIGS. 5 to 7.

2) Results of the experiment

Carbon nanotubes exist as nanofillers in polymers and generally exhibit a phenomenon in which carbon nanotubes are coated or filled due to non-covalent adsorption between the polymer and the carbon nanotubes. FIG. 5 is a surface topography of tensile fracture surfaces of LCE, MWNT-AC/LCE, MWNT-UEC/LCE, MWNT-UAC/LCE and MWNT-OH/LCE. As shown in a-c of FIG. 5, the cross-section of the LCE in the transverse direction of the stretching direction is relatively flat and smooth, while the MWNT-AC/LCE and MWNT-UEC/LCE surface form a large number of irregular wrinkles, forming many coarse fibers on the surface. When the MWNT-AC/LCE and MWNT-UEC/LCE are subjected to an external load, the carbon nanotubes are wrapped with a layer of polymer and pulled out, and thus the load is transferred to the carbon nanotubes, thereby forming such wrinkled fracture surfaces. As shown by d-f in FIG. 5, the diameters of MWNT-AC/LCE and MWNT-UEC/LCE are significantly increased compared to MWNT-UAC/LCE, indicating that extremely strong adhesion is formed between the MWNT-AC and MWNT-UEC and the LCE matrix. As shown by e-g in FIG. 5, MWNT-AC and MWNT-UEC are more easily dispersed in the solution of the liquid crystalline elastomer than MWNT-OH, thus indicating that MWNT-AC and MWNT-UEC are more easily dispersed into the liquid crystalline elastomer matrix than MWNT-OH. In summary, in addition to non-covalent interactions, covalent interactions play an important role in the dispersion of carbon nanotubes in the intrinsic liquid crystal elastomer matrix.

To further understand the structure of the intrinsic carbon nanotube/liquid crystal elastomer, the MWNT-AC/LCE was observed in a cross-sectional view using a scanning electron microscope, a double-spherical aberration correction analysis type field emission transmission electron microscope and an atomic force microscope, respectively. As shown in a-b of FIG. 6, in MWNT-AC/LCE, "stripe-like structures" formed by coating carbon nanotubes with a polymer are preferentially aligned in the same direction, resulting in good orientation. The purple region is a relatively small sample prepared from frozen ultrathin sections and about 1 μm thick, forming "wrinkles" on the copper mesh, as shown in a in fig. 6. The "striped" structure was also found in the double spherical aberration correction analysis type field emission transmission electron microscope and atomic force microscope images, as shown in c to d in fig. 6. In the atomic force microscope image, the structure of the carbon nanotubes can be seen to exist on the "stripe-like structure", which also proves that the stripe-like structure is formed by coating the carbon nanotubes with the polymer.

Further, the dispersion of the carbon nanotubes in MWNT-AC/LCE was observed by a 120kV transmission electron microscope. In FIG. 7, a-f are morphology diagrams taken by taking different areas of MWNT-AC/LCE, and it can be seen from the diagrams that MWNT-AC forms good dispersion and orientation in the liquid crystal elastomer matrix, and no obvious agglomeration phenomenon is found, which indicates that the method for synthesizing the intrinsic type liquid crystal elastomer preliminarily solves the problem of agglomeration and orientation of the carbon nanotubes in the polymer matrix.

(3) Orientation analysis of intrinsic carbon nanotube/liquid crystal elastomer

1) Experimental methods

Optical images of the samples prepared in example 1 and comparative example 5 taken on a polarizing microscope instrument with a cold and hot stage. The prepared monodomain state samples were observed at room temperature by alternately rotating the sample stage at 45 ° and 90 °. The results are shown in FIG. 8.

2) Results and discussion

FIG. 8 is a polarized photograph of a sample in a monodomain state, and from a and c in FIG. 8, it can be seen that the polarized photographs of LCE and MWNT-AC/LCE show the brightest state, indicating that the mesogen is at about 45 to the polarizer direction; rotating the sample by 45 degrees, the LCE and MWNT-AC/LCE change from light to dark (as shown in b and d in FIG. 8), indicating that the mesogen is perpendicular or parallel to the polarizer, and that the mesogen in the monodomain carbon nanotube/LC elastomer aligns preferentially in the same direction.

2. Mechanical property, thermal stability and ultraviolet-visible-near infrared spectrum analysis of intrinsic carbon nanotube/liquid crystal elastomer

(1) Mechanical property analysis of intrinsic carbon nanotube/liquid crystal elastomer

1) Experimental methods

The tensile properties of the samples prepared in examples 1-2 and comparative examples 1-5 were tested using a universal tensile tester. After curing the sample stretched uniaxially twice under an ultraviolet lamp for 15min, the sample was cut into strips having a length of about 9mm and a width of about 3mm in the transverse and longitudinal directions, respectively, of the stretching direction. All the sample strips were tested at room temperature using a universal tensile tester (UTM5202), with a tensile rate of 5mm/min and a sensor of 50N. The results are shown in FIG. 9.

The samples prepared in examples 1-2 and comparative examples 3 and 5 were tested for light-induced mobility using a universal tensile tester. Fixing the sample on a universal drawing machine, controlling the displacement to be 1mm/min, controlling the force to be 0.01N, and respectively using ultraviolet laser and infrared laser with different power densities to alternately switch and irradiate so as to explore the relationship and the stability between the light power densities of the ultraviolet laser and the infrared laser and the actuating stress. Meanwhile, the temperature of the sample surface was measured using a thermal infrared imager, and the relationship between the sample temperature and the optical power density was analyzed using FLIR Tools + software. The results are shown in FIG. 10.

2) Results and discussion

The stress-strain curves in the transverse direction a and the longitudinal direction b along the tensile direction of the sample are shown in fig. 9. The tensile strength in the transverse direction (shown as a in FIG. 9) of MWNT-UAC/LCE was increased by 142%, while those of MWNT/LCE, MWNT-OH/LCE and MWNT-PC/LCE were increased by 78.9%, 86.8% and 53.0%, respectively, as compared with LCE. On one hand, the carbon nano tube has the properties of high modulus and high length-diameter ratio; on the other hand, due to the grafting of the alkyl chain, the steric hindrance between the carbon nano tubes is increased, and the agglomeration of the carbon nano tubes is effectively prevented. As can be seen from c in FIG. 9, the average tensile strength stresses of MWNT-AC/LCE and MWNT-UEC/LCE reached 13.87MPa and 12.12MPa, respectively. Compared with MWNT-PC/LCE and MWNT-UAC/LCE, the MWNT-AC/LCE and MWNT-UEC/LCE are respectively increased by 2.39 times and 1.9 times. The main reason is that the carbon-carbon double bonds of MWNT-AC, MWNT-UEC and RM82 can react with sulfydryl on thiol to form a slightly crosslinked network, and form good dispersion in the matrix, and the compatibility between the carbon nanotubes and the liquid crystal elastomer is improved.

It is worth noting that the tensile strength of MWNT-AC/LCE and MWNT-UEC/LCE is obviously improved, which may depend on that the distance between the benzene rings of the functionalized carbon nano-tube (MWNT-AC) in MWNT-AC/LCE and the mesogen is smaller, and stronger pi-pi interaction is formed. Compared with LCE, the MWNT-AC/LCE has the tensile strength increased by 4.2 times and shows obvious tensile property, which is mainly attributed to the fact that the covalent crosslinking and the pi-pi conjugation function jointly enhance the interface adhesion between the carbon nano tube and the liquid crystal elastomer and improve the compatibility between the carbon nano tube and the liquid crystal elastomer. The ratio of the transverse to longitudinal tensile strength of each sample was about 2 to 4 times (as shown in FIG. 9), indicating that all samples developed anisotropic mechanical properties after two stretches.

FIG. 10 shows actuation stress curves generated by MWNT-AC/LCE, MWNT-UEC/LCE, MWNT-OH/LCE and LCE under infrared laser and ultraviolet laser irradiation and actuation stability curves at fixed infrared laser density and fixed ultraviolet laser density. As shown in a and c of FIG. 10, the actuating stresses of MWNT-AC/LCE, MWNT-UEC/LCE and MWNT-OH/LCE increase with increasing optical power density, wherein the MWNT-AC/LCE has an infrared laser power density of413mW/cm²When the pressure reaches the maximum value of 1.66 MPa; the power density of ultraviolet laser is 608mW/cm²When the pressure reaches the maximum, the actuating stress reaches 1.28 MPa. As shown in B and d in FIG. 10, MWNT-AC/LCE, MWNT-UEC/LCE, MWNT-OH/LCE and LCE all maintain relatively high stability under the irradiation of infrared laser alternating switch; relatively high stability is also maintained under the irradiation of the ultraviolet laser alternating switch. The actuating stress of LCE after infrared laser triggering is almost zero, and the actuating stress of 0.6MPa is generated after ultraviolet light excitation, which also corresponds to that LCE has almost no absorption peak in the infrared region of the ultraviolet-visible-near infrared spectrum and has an absorption peak in the ultraviolet region.

(2) Thermal stability analysis of intrinsic carbon nanotube/liquid crystal elastomer

1) Experimental methods

The thermal stability of the samples prepared in examples 1-2 and comparative examples 1-5 was tested using a thermogravimetric analyzer. The samples were dried in a vacuum oven at 60 ℃ for 12h, about 10mg each, and tested under nitrogen using a thermogravimetric analyzer (TA449F3) under the following conditions: the temperature is raised from 25 ℃ to 600 ℃ at a heating rate of 10 ℃/min. The results are shown in FIG. 11.

2) Results and discussion

The decomposition temperature (temperature corresponding to 5% decomposition) of all samples was measured to be between about 350 ℃ and 470 ℃ (as shown in figure 11). This indicates that the addition of carbon nanotubes does not improve the thermal stability of the liquid crystal elastomer matrix, probably because the amount of carbon nanotubes added is relatively small. It also shows that the addition of carbon nanotubes does not affect the decomposition mechanism of the liquid crystal elastomer.

(3) Ultraviolet-visible-near infrared spectrum analysis of intrinsic carbon nanotube/liquid crystal elastomer

1) Experimental methods

The ultraviolet-visible-near infrared spectra of the raw material of example 1 and the sample prepared in comparative example 5 were obtained by an ultraviolet-visible-near infrared (UV-VIS-NIR) spectrophotometer (Cary 5000). The starting material was dissolved in toluene to form a homogeneous solution having a concentration of about 0.001 mg/mL. The mixed solution was diluted with toluene to a 5% solution, dropped on quartz glass, thermally polymerized in a vacuum oven at 60 ℃, and cooled for testing. And measuring the absorption of all samples in the wavelength range of 200-1200 nm by using a UV-VIS-NIR spectrophotometer. The results are shown in FIG. 12.

2) Results and discussion

LCEs absorb strongly at wavelengths of 261nm and 265nm (as shown in fig. 12), which means that liquid crystal elastomers can trigger actuation under uv light irradiation. And MWNT-AC/LCE shows wide absorption in the 200-1200 nm region, which indicates that the carbon nanotube-containing liquid crystal elastomer can be triggered and actuated by infrared light, ultraviolet light and visible light.

3. Analysis of thermal and photo-dynamic stability of intrinsic carbon nanotube/liquid crystal elastomer and its actuator

(1) Analysis of thermal actuation stability of intrinsic carbon nanotube/liquid crystal elastomer

1) Experimental methods

The stability of reversible thermal actuation was studied by measuring the change in length of the samples prepared in examples 1-2 and comparative example 5 during alternating cooling (room temperature) and heating (180 ℃). To ensure the accuracy of the data, each sample was cycled 50 times. The results are shown in FIG. 13.

2) Results and discussion

FIG. 13, a, illustrates that MWNT-AC/LCE exhibits two-stage deformation during cooling, exhibiting a flattened state at 180 ℃ and a length of 18.5 mm. When the temperature is reduced to 115 ℃, the MWNT-AC/LCE curls; cooling to 100 ℃, and enabling the curling degree to be maximum and to be approximate to a circle; as the temperature continues to drop, the MWNT-AC/LCE stretches back and forth; finally, at room temperature, the steel sheet returns to the flattened state. In this process, the MWNT-AC/LCE splines grow in length and become smaller in width. When the temperature is raised to 180 ℃ again, the MWNT-AC/LCE returns to the original state, which shows that the intrinsic MWNT-AC/LCE shows two-stage deformation in the heating stage and the cooling stage, and the deformation process is reversible. As can be seen from b-d in FIG. 13, MWNT-AC/LCE has the highest actuation stability. Further, we have found that the degree of deformation of the liquid crystal elastomer is greatly related to the stretching ratio at the stage of photopolymerization.

Different from the liquid crystal elastomer added with the carbon nano tube, LCE with different tensile deformation has a hysteresis window in the cooling process. This is probably because the carbon nanotubes in the intrinsic carbon nanotube/liquid crystal elastomer are dispersed uniformly and have good compatibility with the matrix, and can rapidly transfer heat to the whole matrix, which also indicates that the dispersion and orientation of the carbon nanotubes contribute to reducing the hysteresis of deformation.

(2) Photoinduced dynamic stability analysis of intrinsic carbon nanotube/liquid crystal elastomer

1) Experimental methods

The temperature change of the surface of the samples prepared in examples 1 to 2 and comparative examples 3 and 5 was measured by alternately turning on and off the infrared laser to obtain the photodynamic stability. The results are shown in FIG. 14.

2) Results and discussion

FIG. 14 is a graph of the intrinsic type carbon nanotube/liquid crystal elastomer (examples 1 and 2) and MWNT-OH/LCE (comparative example 3) at 318mW/cm, respectively²、604mW/cm²And 870mW/cm²And (3) a relation graph between the infrared laser power density and the surface temperature of the sample and a corresponding infrared image. In fig. 14 a-c it can be seen that under different ir laser densities, the following holds: t is a unit of_MWNT-AC/LCE>T_MWNT-UEC/LCE>T_MWNT-OH/LCE>T_LCEThe highest photothermal conversion efficiency of MWNT-AC/LCE is seen, which is mainly due to the fact that the distance between the carbon nano tube (MWNT-AC) in the MWNT-AC/LCE and the benzene ring of the liquid crystal element is smaller, and a stronger pi-pi interaction is formed, so that the covalent crosslinking and the pi-pi conjugation jointly enhance the interface adhesion between the carbon nano tube and the liquid crystal elastomer, and effectively improve the compatibility of the carbon nano tube in the liquid crystal elastomer matrix. The temperature of the sample surface increases with increasing optical power density, e.g., MWNT-AC/LCE, at an infrared laser power density of 318mW/cm²At the temperature of 77.8 ℃; the optical power density is adjusted to 604mW/cm²When the temperature reaches 126.4 ℃; the optical power is continuously increased to 870mW/cm²The temperature rose to 150.2 ℃. And the actuating speed of all samples is faster than the recovery speed, which is mainly because the carbon nano tube exerts the nanometer after receiving the laser signalThe heater is operated to drive the temperature of the MWNT-AC/LCE to the phase transition temperature within 6 seconds, and the recovery process is achieved by air convection.

Furthermore, the deformation of the MWNT-AC/LCE can be point-controlled or area-controlled. By measuring the load bearing limit of the carbon nanotube/liquid crystal elastomer, it can be measured that the MWNT-AC/LCE of 36mg can lift up a weight of 210g at the maximum, and only a weak deformation occurs. This clearly demonstrates its strong mechanical properties and its reversible recovery.

(3) Thermal actuation and photo-actuated stability analysis of intrinsic carbon nanotube/liquid crystal elastomer actuators

1) Experimental methods

The actuator samples prepared in example 5, example 6 and comparative example 6 were tested for thermal and photo-dynamic stability by the same method as for thermal and photo-dynamic stability of the intrinsic type carbon nanotube/liquid crystal elastomer described above. The results are shown in FIGS. 15 and 16.

2) Results and discussion

As can be seen from a-c in FIG. 15, the multilayer MWNT-AC/LCE actuator can respond to infrared laser light, ultraviolet laser light, and temperature changes, and can provide a near infrared laser power density of 604mW/cm²Under irradiation, 10s reached the phase transition temperature (84 ℃) and the temperature rose to a maximum of 110 ℃ and showed a steady temperature change during the switching cycle. The intelligent device is a novel intelligent device and has high application value in advanced application programs.

The bending degree of the liquid crystal elastomer can be adjusted by controlling the infrared laser point. When infrared laser is irradiated on the surface of the material, the temperature of the sample will be locally raised, forming different temperature gradients. The local phase change of the liquid crystal elastomer is realized by controlling the power and the position of the laser beam, so that the shape of the material is changed. We fabricated a single domain MWNT-AC/LCE wound in a meander around four juxtaposed tubes and fixed in shape under 365nm UV light, the process is shown in FIG. 16, a. As shown in fig. 16 b, since different portions of the actuator are stretched and bent, the liquid crystal cell is given different orientation directions, and thus different degrees of deformation will occur when the near-infrared laser is irradiated to different positions of the actuator. By controlling the irradiation position and power of the near-infrared laser, the actions of straight movement (0-38 s) and turning (38-63 s) of the snake-shaped actuator can be controlled.

In conclusion, the present invention effectively overcomes the disadvantages of the prior art and has high industrial utilization value. The above-described embodiments are intended to illustrate the substance of the present invention, but are not intended to limit the scope of the present invention. It will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the true spirit and scope of the invention.

Claims

1. A preparation method of an intrinsic carbon nanotube/liquid crystal elastomer is characterized by comprising the following steps:

(1) performing functional modification on the carbon nano tube by using a modifying group substance to obtain a functional carbon nano tube grafted with a modifying group; the surface of the functionalized carbon nanotube is provided with a modifying group with a carbon-carbon double bond, and the carbon-carbon double bond is positioned at the tail end of the modifying group;

(2) adding a liquid crystal element and a photoinitiator into a solvent, and dissolving to obtain a solution; the liquid crystal element is one or two of RM82 and RM 257;

(3) adding a cross-linking agent, a spacer substance, a catalyst and the functionalized carbon nano tube into the solution prepared in the step (2), and uniformly stirring to obtain a dispersion liquid a; the chain ends of the cross-linking agent and the spacer substance both contain sulfydryl;

2. The method of claim 1, wherein the carbon nanotube is at least one of a hydroxylated carbon nanotube, an aminated carbon nanotube, and a carboxylated carbon nanotube, and the modifying group is at least one of 10-undecylenoyl chloride, 10-undecylenic alcohol, acryloyl chloride, 4-pentenoyl chloride, 10-undecylenic acid, and 11-dodecenoic acid.

3. The method for preparing intrinsic carbon nanotube/liquid crystal elastomer according to claim 2, wherein the step (1) of using the modifying group substance to functionally modify the carbon nanotubes comprises the following steps:

2) dripping a catalyst into the carbon nano tube dispersion liquid under the atmosphere of protective gas, and uniformly stirring to obtain a mixed liquid;

4. The method for preparing an intrinsic carbon nanotube/liquid crystal elastomer as claimed in claim 3, wherein the molar ratio of the active group of the carbon nanotube, the modifying group substance and the catalyst in the process of performing the functional modification on the carbon nanotube is 1: 2-10, wherein the active group of the hydroxylated carbon nanotube is hydroxyl, the active group of the carboxylated carbon nanotube is carboxyl, and the active group of the aminated carbon nanotube is amino.

5. The method of claim 1, wherein the spacer material is at least one of 1, 2-ethanedithiol, 1, 3-propanedithiol, 1, 5-pentanethiol, 1, 6-hexanedithiol, 1, 8-octanethiol, 1, 9-nonanedithiol, 1, 10-decanedithiol, and 3, 6-dioxa-1, 8-octanethiol.

6. The method of claim 1, wherein the cross-linking agent is at least one selected from pentaerythritol tetrakis (3-mercaptopropionate), pentaerythritol tetrakis (mercaptoacetate), trimethylolpropane tris (3-mercaptopropionate), and dipentaerythritol hexa (3-mercaptopropionate).

7. The method for preparing an intrinsic carbon nanotube/liquid crystal elastomer according to claim 1, wherein the mass ratio of the mesogen, the crosslinking agent and the spacer is (50-80) to (5-10) to (10-15.5), the mass of the functionalized carbon nanotube is 0.05-5% of the sum of the mass of the mesogen, the crosslinking agent and the spacer, the mass of the catalyst is 0.1-0.57% of the sum of the mass of the mesogen, the crosslinking agent and the spacer, and the mass of the photoinitiator is 2-8% of the sum of the mass of the mesogen, the crosslinking agent and the spacer.

8. The method for preparing an intrinsic carbon nanotube/liquid crystal elastomer according to claim 1, wherein the carbon nanotube is one or two of a single-walled carbon nanotube and a multi-walled carbon nanotube, and the carbon nanotube has a diameter of 0.5-10 nm and a length of 2-50 μm.

9. An intrinsic carbon nanotube/liquid crystal elastomer product prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the intrinsic carbon nanotube/liquid crystal elastomer product of claim 9 in an actuator.