CN113683890B

CN113683890B - Silicone rubber-based electro-driven composite material and preparation method thereof

Info

Publication number: CN113683890B
Application number: CN202111068535.9A
Authority: CN
Inventors: 刘正英; 赵咨宇; 许泽旺; 黄炎昊; 杨伟; 杨鸣波
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2021-09-13
Filing date: 2021-09-13
Publication date: 2022-12-20
Anticipated expiration: 2041-09-13
Also published as: CN113683890A

Abstract

The invention belongs to the field of electrodrive elastomers, and particularly relates to a silicon rubber-based dielectric elastomer and a preparation method thereof. The invention provides a preparation method of a silicon rubber-based electro-driven composite material, which comprises the following steps: firstly, constructing a three-dimensional network framework of silicon rubber/conductive filler; then, packaging the three-dimensional network framework by using a silicone rubber prepolymer; finally, a silicon rubber network is formed through heating and curing and interpenetrated with the silicon rubber/conductive filler three-dimensional network, and the silicon rubber-based electro-driven composite material with an isolated silicon rubber/conductive filler three-dimensional network structure inside is formed. The silicon rubber-based electrodrive composite material obtained by the invention has the characteristics of high dielectric constant, low modulus and high electrodeformation.

Description

Silicone rubber-based electro-driven composite material and preparation method thereof

Technical Field

The invention belongs to the field of electrodrive elastomers, and particularly relates to a silicone rubber-based dielectric elastomer with a high dielectric constant, low modulus and high electrodeformation and an isolated three-dimensional filler network structure and a preparation method thereof.

Background

The carbon-series particle-filled silicone rubber-based nano composite material is a dielectric elastomer with great application prospect, has the advantages of high energy density, high response speed, low modulus, good flexibility, high electromechanical conversion efficiency and the like, and has good application prospect in various fields such as artificial skin, artificial muscle, bionic robot and the like. After an electric field is applied to the filled silicon rubber-based dielectric elastomer coated with the flexible electrode, because various polarization actions generate polarization charges on the dielectric elastomer/conductive particle interfaces, different polarization charges on different interfaces attract each other, and the same polarization charges on the same surface repel each other, so that the dielectric elastomer is compressed along the direction of the electric field, the area in the direction vertical to the electric field is increased, the purpose of converting electric energy into mechanical energy is realized, and the function of electrodrive is achieved. According to the driving mechanism of the dielectric elastomer composite, the electrical driving performance of the dielectric elastomer is proportional to its dielectric constant and inversely proportional to the elastic modulus of the material. The more the carbon-based conductive particles are, the more polarizable interfaces in the composite material are, the more the dielectric properties of the composite material can be improved to a greater extent, but as an electrically-driven composite material, the requirement for low modulus and low loss is inevitably required, and the content of the conductive particles introduced into the dielectric elastomer is required to be as low as possible or the particle distribution is required to be as uniform as possible. Such a pair of contradictions makes the structural design of the dielectric elastomer critical.

The three-dimensional high dielectric particle network is fixed by using thermosetting materials such as epoxy resin and the like, so that the content of a polarization interface can be effectively increased, the content of used inorganic particles (Energy & Environmental Science,2017,10, 137-144) can be reduced, and the composite material has more excellent dielectric properties under the condition of lower filler content (the dielectric constant reaches 60@1khz when the particle volume fraction is 25 vol.%). The polyvinylidene fluoride and the carbon nano tube can also be used for preparing a three-dimensional framework structure of the conductive filler by using an ice template method, epoxy resin is filled into the framework to prepare the composite material with the three-dimensional conductive framework inside, the dielectric property of the composite material is greatly improved under the condition of extremely low filler content, and when the content of the carbon tube is 0.25wt%, the dielectric constant of the composite material reaches 170@100Hz (Composites, part B,2019, 171. However, these methods result in a large increase in the modulus of the dielectric composite material, and are not favorable for its use as an electrodrive material.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides a silicone rubber-based electrodrive composite material with a three-dimensional filler network structure, and the obtained electrodrive composite material has the characteristics of high dielectric constant, low modulus and high electrodeformation.

The technical scheme of the invention is as follows:

the first technical problem to be solved by the invention is to provide a preparation method of a silicone rubber-based electro-driven composite material, which comprises the following steps: firstly, constructing a three-dimensional network framework of silicon rubber/conductive filler; then, packaging the three-dimensional network framework by using a silicone rubber prepolymer; finally, a silicon rubber network is formed through heating and curing and interpenetrated with the silicon rubber/conductive filler three-dimensional network, and the silicon rubber-based electro-driven composite material with an isolated silicon rubber/conductive filler three-dimensional network structure inside is formed.

Furthermore, the mass fraction of the conductive filler (namely the mass ratio of the conductive filler to the total mass of the three-dimensional network framework) is 0.2-0.8%.

Further, the conductive filler is selected from the group consisting of: at least one of multiwall carbon nanotubes (MWCNTs), reduced Graphene (GO), or Carbon Black (CB).

Further, the silicon rubber/conductive filler three-dimensional network skeleton can be constructed by adopting a sacrificial template method, and the specific method comprises the following steps: and immersing the silicon rubber/conductive filler suspension into a template to enable the suspension to be attached to the template, and etching the template in etching liquid after curing to obtain the three-dimensional network framework.

Further, the template used in the sacrificial template method is nickel foam, and the etching solution used is ferric chloride (FeCl) ₃ ) FeCl with the concentration of 0.5-2M prepared from the hydrochloric acid solution (HCl) ₃ And (3) solution.

Further, the preparation method of the silicon rubber-based electro-driven composite material comprises the following steps:

1) Forming a suspension by using a conductive filler and a solvent, and then uniformly dispersing a silicone rubber prepolymer in the suspension to obtain a silicone rubber prepolymer/conductive filler suspension;

2) Immersing the template into the silicone rubber prepolymer/conductive filler suspension to uniformly attach the silicone rubber prepolymer/conductive filler suspension to the template, taking out the template, drying and curing; then, placing the cured sample in etching solution for etching to obtain a silicone rubber/conductive filler three-dimensional network framework;

3) And (3) encapsulating the silicone rubber/conductive filler three-dimensional filler network framework obtained in the step 2) by using a silicone rubber prepolymer, and drying and curing the silicone rubber/conductive filler three-dimensional filler network framework to obtain the silicone rubber-based electro-driven composite material (dielectric elastomer) with the isolated silicone rubber/conductive filler three-dimensional filler network structure.

Further, in the step 1), the mass concentration of the silicone rubber prepolymer/conductive filler suspension is 18.3% -19.7%. The amount of solvent added in step 1) of the present invention is required to enable the filler to be uniformly dispersed.

Further, in the step 1), the solvent used is at least one of tetrahydrofuran, dichloromethane, acetone or n-hexane.

Further, in step 1), the conductive filler and the solvent are subjected to ultrasonic treatment to obtain a suspension.

The second technical problem to be solved by the invention is to provide a silicone rubber-based electro-driven composite material which is prepared by adopting the method.

Furthermore, in the silicon rubber-based electro-driven composite material, a silicon rubber network and a silicon rubber/conductive filler three-dimensional network are mutually penetrated, and an isolated silicon rubber/conductive filler three-dimensional network structure is arranged in the silicon rubber-based electro-driven composite material, so that the conductive filler is only distributed in a framework area of the silicon rubber/conductive filler three-dimensional network.

The invention has the beneficial effects that:

(1) The electro-driven composite material prepared by the invention has an isolated three-dimensional filler network structure, and the isolated three-dimensional filler network structure enables fillers in the composite material to be distributed in a local network framework region only, so that the usage content is low, and the influence of the introduction of the fillers on the degradation of mechanical properties is reduced.

(2) The distance between particles in the filler skeleton is reduced along with the increase of the content of the filler, charges can migrate among the particles under the action of an electric field, adjacent particles can be regarded as a micro-capacitor structure, a large amount of polarized charges can be stored, so that the obtained electrically-driven composite material with the isolated three-dimensional filler network structure has a high dielectric constant under the condition of low filler content, and the electric actuation sensitivity factor of the composite material is improved, for example, when the content of carbon nano tube particles (MWCNT) is 0.6%, and when Ecoflex is selected as the silicon rubber, the obtained dielectric elastomer with the isolated silicon rubber/conductive filler three-dimensional network structure (3D-MWCNT-0.6/Ecoflex composite material) is applied to a low electric field (10 kV mm) by the aid of the silicon rubber ^-1 ) And the actuation strain is 11.61% larger under the condition without pre-strain, which is improved by 7.8 times compared with the pure sample.

(3) The material obtained by the invention has a three-dimensional network structure with a uniform structure, and the network structure has strong adjustability (the mesh number and the framework size of the used nickel template are adjustable, and the relative size of the network structure with a conductive function and the network structure with an insulating function in the composite material can be changed by using different nickel templates, so that the overall network structure of the final composite material is adjusted), and meanwhile, the composite material containing the three-dimensional network structure can be ensured to have high dielectric constant, low modulus and higher driving strain capacity.

Description of the drawings:

FIGS. 1a and b are SEM photographs of the three-dimensional MWCNT/Ecoflex framework network structure obtained in example 2, wherein FIG. 1b is an enlarged cross-sectional view of the framework structure; FIG. 1c, D is an SEM photograph of the final encapsulated 3D-MWCNT/Ecoflex composite; the bright spots in the figure are MWCNT particles.

FIG. 2a is a stress-strain curve for different MWCNT contents for examples 1-4, and FIG. 2b is an enlarged view of the strain range of 0-25%.

FIGS. 3 (a), (b) and (c) are graphs showing the changes of dielectric constant, dielectric loss and conductivity at room temperature for 3D-MWCNT/Ecoflex composites with different MWCNT contents corresponding to examples 1 to 4.

FIG. 4 is a graph showing the driving deformation curves of 3D-MWCNT/Ecoflex composites with different MWCNT contents under different electric fields according to examples 1-4.

The specific implementation mode is as follows:

the invention aims to solve the technical problem of providing a preparation method of a silicon rubber-based electro-driven composite material, which comprises the following steps: firstly, constructing a three-dimensional network framework of silicon rubber/conductive filler; then, packaging the three-dimensional network framework by using a silicone rubber prepolymer; finally, a silicon rubber network is formed through heating and curing and interpenetrated with the silicon rubber/conductive filler three-dimensional network, and the dielectric elastomer with the isolated silicon rubber/conductive filler three-dimensional network structure inside is formed. The insulating network and the conductive network are interpenetrating, so that the insulating network isolates the disordered distribution of the conductive network in the whole space; thereby reducing the use of conductive particles and achieving low modulus and low dielectric loss of the resulting composite.

The method adopts a sacrificial template method to prepare the three-dimensional network framework of the conductive filler firstly, and then packages the conductive filler by using pure Ecoflex, so that on one hand, the conductive filler is not randomly distributed in the whole matrix but only distributed in the three-dimensional network framework prepared by the sacrificial template method, and under the condition of the same filler content, when the filler is only distributed in the three-dimensional network framework, the density of the filler is far higher than that of the filler in the random distribution, and the average distance among particles of the filler is far smaller than that of the filler in the random distribution; this in turn leads to composites of the invention which can achieve percolation values at lower filler contents. On the other hand, the pure silicon rubber with low modulus plays an isolation role, and on the basis of ensuring that the modulus of the composite material is not increased, the dielectric loss or the electric breakdown characteristic of the composite material can be reduced, so that the obtained material can be used as an electro-driver.

Examples 1 to 4

Raw materials: the reaction mixture of tetrahydrofuran and water is taken as a reaction mixture,

0030 silicone rubber, multiwalled carbon nanotubes, nickel foam, ferric chloride hexahydrate (fecl3.6h2o), hydrochloric acid (HCl); wherein, the multi-wall carbon nano-tube accounts for 0.2 percent, 0.4 percent, 0.6 percent and 0.8 percent of the total mass of the three-dimensional network framework respectively.

The preparation method comprises the following steps:

(1) Carrying out ultrasonic treatment on a certain amount of multi-walled carbon nanotubes in 40ml of tetrahydrofuran for 1 hour, adding 9g of Ecoflex silicon rubber into the obtained multi-walled carbon nanotube suspension, and continuing to carry out ultrasonic treatment for 15 minutes to obtain a uniformly dispersed MWCNT/Ecoflex suspension;

(2) Immersing nickel foam into the MWCNT/Ecoflex suspension obtained in the step (1) to enable the suspension to be uniformly attached to a nickel framework, taking out the nickel foam, and placing the nickel foam in a vacuum drying oven at 80 ℃ for half an hour to enable the silicon rubber matrix to be fully cured; 200ml of 1mol/L FeCl are subsequently prepared ₃ Dripping a small amount of hydrochloric acid into the aqueous solution to obtain etching solution; soaking the cured sample in an etching solution for 24 hours to fully etch away the metallic nickel, thereby obtaining the MWCNT/Ecoflex three-dimensional filler network skeleton; wherein the mass percentages of the multi-wall carbon nanotubes in the three-dimensional network skeleton are respectively 0.2% (example 1), 0.4% (example 2), 0.6% (example 3) and 0.8% (example 4);

(3) And (3) packaging the network framework obtained in the step (2) by using pure silicon rubber, and drying the network framework in a vacuum drying oven at the temperature of 80 ℃ for half an hour to solidify the silicon rubber to obtain the composite material with the isolated three-dimensional filler network structure inside.

The morphology, mechanical properties, thermal properties, dielectric properties and electric drive properties of the composite material obtained in the examples were tested and characterized:

observing the micro-morphology of the sections of the MWCNT/Ecoflex three-dimensional filler framework and the 3D-MWCNT/Ecoflex composite material by adopting an aspect F type scanning electron microscope of FEI company; and (3) brittle fracture of the sample by using liquid nitrogen and spraying gold on the section, wherein the accelerating voltage is 20kV.

FIGS. 1a, b are SEM pictures of three-dimensional MWCNT/Ecoflex framework network structure in example 2, wherein, FIG. b is a cross-sectional enlarged view of the framework structure, and FIG. 1c, D is SEM picture of the finally obtained 3D-MWCNT/Ecoflex composite material; the bright spots in the figure are MWCNT particles. As can be seen from fig. 1a and b, the three-dimensional framework structure of the metallic nickel foam is repeatedly engraved, and the hollow MWCNT/Ecoflex three-dimensional network framework structure is successfully prepared, and from the enlarged view of the framework section, it can be seen that the MWCNT particles can be uniformly dispersed in the framework formed by the Ecoflex matrix, and no significant agglomeration phenomenon occurs. Fig. 1c and 1d show that the skeleton structure is packaged with pure Ecoflex to a relatively good extent, but due to the good flexibility of Ecoflex, a small portion of the skeleton after the nickel metal is etched away fails to maintain a good hollow structure (partial collapse), so that pure Ecoflex does not completely fill the skeleton structure. In summary, from the SEM characterization results of the three-dimensional MWCNT/Ecoflex framework network structure and the final sample, it can be considered that the 3D-MWCNT/Ecoflex composite material having the three-dimensional filler network structure inside is successfully prepared.

The tensile test was carried out using an Autograph AGS-J type tensile machine of Shimadzu corporation, japan: making the composite material into a dumbbell-shaped sample strip for tensile test, wherein the sample size is 2cm multiplied by 0.35cm multiplied by 0.02cm, and the tensile rate is 50mm/min; the young's modulus of the composite was calculated using stress strain data within 10% strain. FIG. 2a is the stress-strain curve corresponding to different MWCNT contents in examples 1-4, and FIG. 2b is an enlarged view of the strain range 0-25%; as can be seen from FIG. 2a, the elongation at break of the 3D-MWCNT/Ecoflex composite material slightly decreases as the MWCNT content in the framework structure increases.

Table 1 shows the dielectric constant at 1kHz, the elastic modulus, the electric actuation sensitivity factor, the actuation deformation at an electric field strength of 7V/. Mu.m, the breakdown voltage, and the maximum drive deformation for different MWCNT contents for examples 1-4. As can be seen from table 1, as the MWCNT content increases, the elastic modulus of the composite increases, but the magnitude is so gentle that the elastic modulus of the composite is always maintained at a lower value. The elastic modulus of the samples with 3D-MWCNT-0.8/Ecoflex composite material was increased to 0.112MPa and 0.128MPa with a small margin compared to 0.09MPa for pure Ecoflex.

TABLE 1 summary of sensitivity factor (. Beta. = ε/Y) and driven strain performance of 3D-MWCNT/Ecoflex composites

Cutting the obtained 3D-MWCNT/Ecoflex composite material into samples with the diameter of 5cm and the thickness of 0.2mm, coating low-temperature curing conductive silver paste on the upper surface and the lower surface, and then adopting a Concept 80 type broadband dielectric spectrum tester to test the dielectric property, wherein the test conditions are room temperature, and the test frequency range is 10Hz to 10Hz ⁷ Hz。

FIGS. 3a, b, c show the dielectric constant, dielectric loss and conductivity of 3D-MWCNT/Ecoflex composites at room temperature for different MWCNT contents, and the dielectric performance data at 1kHz is summarized in Table 1. As can be seen from fig. 3 and table 1, the dielectric constant of the composite material rapidly increases with increasing MWCNT content; at a frequency of 1kHz, the dielectric constant of pure Ecoflex was 2.17, while the dielectric constant of sample 3D-MWCNT-0.8/Ecoflex increased to 10.39. Meanwhile, as can be seen from fig. 3a, b, when the MWCNT content in the composite material skeleton structure is small, the dielectric constant of the dielectric elastomer slowly increases with the increase of the filler content and there is substantially no frequency dependence, and the dielectric loss thereof is also always kept below 0.02. When the MWCNT content in the framework structure reaches 0.6wt%, the dielectric constant is greatly increased, and the dielectric constant has a certain frequency dependence and is reduced with the increase of the frequency. Also, the dielectric loss of the composite material increases, and the trend is similar to the increasing trend of the dielectric constant. From fig. 3c, it can be seen that all 3D-MWCNT/Ecoflex composites maintain good insulation, because when the three-dimensional filler network framework is filled with pure Ecoflex, the framework structure is encapsulated inside to form an isolated network structure, and the sample is prevented from conducting electricity to destroy the electric driving performance. At the same time, this also prevents high conductance losses due to leakage currents resulting from the formation of the conductive network.

The 3D-MWCNT/Ecoflex composite material is cut into a sample with the diameter of 5cm and the thickness of 0.2mm, a direct current voltage is applied to the dielectric elastomer sample under the control of a digital box, and the shape change of an electrode part of the sample under the stimulation of an electric field is photographed by a digital camera. Coating flexible electrodes on the upper surface and the lower surface of a 3D-MWCNT/Ecoflex composite material sample, applying voltage (0-5 kV) to the flexible electrodes of the sample, shooting change images of the flexible electrodes under different voltages, and calculating the area of an electrode area by using Photoshop software. The experimental temperature was room temperature.

FIG. 4 is a graph showing the driving deformation curves of 3D-MWCNT/Ecoflex composites with different MWCNT contents under different electric fields according to examples 1-4. FIG. 4 shows the variation of the driven deformation of 3D-MWCNT/Ecoflex composite material under different electric fields. The actuated deformation of both pure Ecoflex and 3D-MWCNT/Ecoflex composites increases rapidly with increasing electric field strength. 3D-MWCNT-0.6/Ecoflex sample composite at 10V/. Mu.m ^-1 Has the maximum driving deformation (11.61%) at the electric field strength of (c). As the MWCNT content increases, the electrostriction of the 3D-MWCNT/Ecoflex composite material at the same lower field strength is also larger, for example, when the electric field strength is 7V/μm, the actuation deformation of 3D-MWCNT-0.8/Ecoflex reaches 8.63% which is 10.2 times that of the pure sample. However, when the content of the conductive filler in the internal network skeleton of the composite material is high, the electrical breakdown strength of the composite material is remarkably reduced.

Claims

1. A preparation method of a silicone rubber-based electro-driven composite material is characterized by comprising the following steps:

1) Forming a suspension by using a conductive filler and a solvent, and uniformly dispersing a silicone rubber prepolymer in the suspension to obtain a silicone rubber prepolymer/conductive filler suspension;

2) Immersing the template into the silicone rubber prepolymer/conductive filler suspension to uniformly attach the silicone rubber prepolymer/conductive filler suspension to the template, taking out the template, drying and curing; then, placing the cured sample in etching liquid for etching to obtain a silicone rubber/conductive filler three-dimensional network framework;

3) Encapsulating the silicon rubber/conductive filler three-dimensional filler network framework obtained in the step 2) by using a silicon rubber prepolymer, and drying and curing the silicon rubber/conductive filler three-dimensional filler network framework to obtain a silicon rubber-based electro-driven composite material with an isolated silicon rubber/conductive filler three-dimensional filler network structure;

wherein the conductive filler accounts for 0.2-0.8% of the total mass of the three-dimensional network framework, and is selected from the following components: at least one of multi-walled carbon nanotubes, reduced graphene, or carbon black.

2. The method for preparing the silastic-based electrokinetic composite material as claimed in claim 1, wherein the template is nickel foam, and the etching solution is FeCl with the concentration of 0.5-2M prepared by aqueous solution of ferric trichloride and hydrochloric acid solution ₃ And (3) solution.

3. The preparation method of the silicone rubber-based electro-driven composite material as claimed in claim 1, wherein in step 1), the mass concentration of the silicone rubber prepolymer/conductive filler suspension is 18.3% -19.7%.

4. The method for preparing the silicone rubber-based electro-active composite material according to claim 1, wherein in step 1), the solvent used is at least one of tetrahydrofuran, dichloromethane, acetone or n-hexane.

5. A silicone rubber-based electro-active composite material, characterized in that the composite material is prepared by the preparation method of any one of claims 1 to 4.

6. The silicone rubber-based electro-active composite material of claim 5, wherein the silicone rubber-based electro-active composite material has a silicone rubber/conductive filler three-dimensional network structure isolated therein by interpenetrating the silicone rubber network and the silicone rubber/conductive filler three-dimensional network.