CN110204850B - Block copolymer thermoplastic dielectric elastomer film and dielectric driver thereof - Google Patents

Abstract

The invention discloses a block copolymer thermoplastic dielectric elastomer film and a dielectric driver thereof. The invention adopts the pre-stretching thermal relaxation technology to the segmented copolymer thermoplastic dielectric elastomer film, can obtain the dielectric elastomer which is free from frame fixation and self-supporting and has thinner thickness, simultaneously improves the driving performance, reduces the driving voltage of the dielectric elastomer, improves the breakdown field strength of the dielectric elastomer and improves the area deformation of the dielectric elastomer. Meanwhile, the dielectric elastomer with anisotropic mechanical property can be obtained through asymmetric pre-stretching thermal relaxation treatment, and the dielectric elastomer can be used for a driver with anisotropic driving property when the driver is driven without a frame, and has important significance in preparing anisotropic flexible drivers and flexible robots from the dielectric elastomer.

Description

A block copolymer thermoplastic dielectric elastomer film and its dielectric actuator

technical field

The invention relates to the field of thermoplastic dielectric elastomers, in particular to a block copolymer thermoplastic dielectric elastomer film and a dielectric driver thereof.

Background technique

The driving mechanism of the dielectric elastomer driver is to coat the upper and lower surfaces of the dielectric elastomer film with flexible electrodes and apply a certain voltage. Due to the different voltages of the upper and lower flexible electrodes, an electric field is formed, thereby generating Maxwell stress to squeeze the dielectric elastomer film, resulting in a reduction in the thickness of the dielectric elastomer film, in-plane expansion, and driving deformation. However, the driving voltage of the general dielectric elastomer driver is relatively high. Usually, the main method to reduce the driving voltage is to reduce the elastic modulus of the material, increase the dielectric constant of the material or the thickness of the smaller film, among which the film thickness of the material is reduced. It is most pronounced for lowering the driving voltage of the dielectric elastomer film.

However, when the thickness of the dielectric elastomer film is thinned and used for dielectric driving, its driving performance will generally decline. This is mainly because the thinning of the dielectric elastomer film is more affected by the defects of the film itself, and the more it is affected by the rigidity of the electrode. The larger it is, the more it is affected by the edge of the electrode. This leads to a decrease in the driving performance of the dielectric elastomer film as the thickness is reduced. Therefore, how to improve the driving performance of dielectric elastomer ultrathin films becomes particularly important. At the same time, among the main methods for preparing thin films such as solution scraping, solution spin coating, and melt extrusion, it is easier to prepare uniform and high-quality thick films than to prepare uniform and high-quality ultra-thin films.

At the same time, the in-plane expansion generated by electrical driving is usually uniform expansion deformation, and it is difficult to achieve anisotropic driving deformation. The general method to achieve anisotropic driving is to maintain a dielectric elastomer with different pre-stretching ratios by using a fixed frame. The film realizes anisotropic drive; it is particularly important to realize the anisotropic drive deformation of the self-supporting frameless dielectric elastomer film, which has broad application prospects in the field of anisotropic drives and flexible robots. The current method to achieve anisotropic driving is mainly to add anisotropic fibers on the dielectric elastomer film (Adv. Mater, 2015, 27, 6814-6819) or introduce anisotropic electrodes, such as anisotropic carbon Nanotube electrodes (Carbon, 2015, 89, 113-120), or the introduction of crystalline units in dielectric elastomers, can achieve anisotropic drive by controlling the orientation of the crystals (Adv. Funct. Mater. 2018, 1803467).

In the invention, a uniform thick film of the block copolymer dielectric elastomer is prepared by scraping the film from a solution, and a thinner dielectric elastomer film can be obtained by pre-stretching and thermal relaxation treatment. Uniform and high-quality ultra-thin films can be prepared by equipolyaxially symmetric pre-stretching thermal relaxation treatment. Through the Weber electrical breakdown test, it is found that the greater the pre-stretching degree, the higher the dielectric elastomer film obtained after thermal relaxation. The breakdown field strength also has a correspondingly better driving performance and a larger driving deformation. By performing anisotropic pre-stretching thermal relaxation treatment on the thermoplastic dielectric elastomer film, a self-supporting dielectric elastomer film that can realize anisotropic driving without frame fixing can be obtained. Different from adding anisotropic fibers to the dielectric elastomer or introducing anisotropic electrodes or introducing crystalline units into the dielectric elastomer, the present invention increases the density of the thermoplastic elastomer by changing the stacking form of the hard segments in the thermoplastic elastomer. Aspect ratio and achieve a certain orientation, so as to obtain anisotropic electrically driven deformation.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a block copolymer thermoplastic dielectric elastomer film and a dielectric driver thereof in view of the deficiencies of the prior art. When the thermoplastic dielectric elastomer film subjected to pre-stretching heat relaxation treatment of the present invention is applied to a dielectric actuator, it has higher driving performance. Self-supporting anisotropic dielectric actuators without frame fixation.

The object of the present invention is achieved by the following technical solutions: a block copolymer thermoplastic dielectric elastomer film, which is prepared by the following method: firstly, the block copolymer thermoplastic dielectric elastomer is uniaxially prestretched , equal biaxial pre-stretching, equal multi-axial pre-stretching or biaxial asymmetric pre-stretching. Among them, the degree of uniaxial pre-stretching is 1 to 20 times of the initial area; the degree of equal biaxial pre-stretching and equal multi-axial pre-stretching is 1 to 30 times of the initial area, and the degree of biaxial asymmetric pre-stretching is 1 to 30 times of the initial area. The stretching ratio is 1 to 400:20; then, under the pre-stretching condition, the pre-stretched block copolymer thermoplastic elastomer is placed in a temperature range of 50 to 150 ° C for thermal relaxation for 0.5 to 20 hours to obtain an embedded A segmented copolymer thermoplastic dielectric elastomer film; the general structural formula of the block copolymer thermoplastic dielectric elastomer is AB-(AB) _n -A, and n is a positive integer. Wherein, A is selected from the homopolymer of styrene, the homopolymer of methyl methacrylate, the copolymer of styrene and methyl methacrylate; B is butyl acrylate homopolymer, n-butyl acrylate homopolymer , n-butyl methacrylate homopolymer, isobutyl methacrylate homopolymer, tert-butyl acrylate homopolymer, 2-ethylhexyl acrylate homopolymer, isooctyl acrylate homopolymer, acrylic acid Ethyl ester homopolymer or butyl acrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, ethyl acrylate A copolymer of at least two monomers in an ester.

Further, the way of maintaining the pre-stretching condition is to fix the block copolymer thermoplastic elastomer on the frame or the non-stick substrate.

Further, in the block copolymer thermoplastic elastomer, A is a hard segment and B is a soft segment; the glass transition temperature of the hard segment is greater than 50°C, and the glass transition temperature of the soft segment is less than -10°C .

Further, the total molecular weight of the block copolymer thermoplastic elastomer is 50,000-500,000, the number-average molecular weight of the hard segment is 0.5-50,000, and the number-average molecular weight of the soft segment is 50,000-400,000, and The soft segment accounts for 60%-95% of the total weight of the block copolymer thermoplastic elastomer.

A dielectric actuator containing the above-mentioned block copolymer thermoplastic dielectric elastomer film, the dielectric actuator is composed of an upper electrode, a block copolymer thermoplastic dielectric elastomer film and a lower electrode connected in sequence.

Further, the upper electrode and the lower electrode are flexible electrodes selected from composite materials of carbon nanotubes, carbon paste, hydrogel, carbon powder and polymer.

The beneficial effects of the present invention are as follows: the present invention applies the thermoplastic elastomer film obtained by pre-stretching thermal relaxation treatment to the field of dielectric actuators, and by controlling the pre-stretching method and the degree of pre-stretching, the achievable driving performance is better. Or a dielectric elastomer film with anisotropy, which leads to better material selection for the application of dielectric elastomer actuators. details as follows:

1. For the thermoplastic elastomer film after pre-stretching and thermal relaxation, the morphology of the hard segment in the initial film will change significantly, and the aspect ratio will increase. The greater the degree of pre-stretching, the greater the aspect ratio.

2. Through uniaxial pre-stretching or biaxial asymmetric pre-stretching thermal relaxation technology, the actuator of the obtained dielectric elastomer film has obvious anisotropy. When the uniaxial pre-stretching thermally relaxed dielectric elastomer actuator is driven by an applied voltage, a small deformation is generated parallel to the stretching direction, and a large deformation is generated perpendicular to the stretching direction. Periodic wrinkling of wavelengths; the greater the degree of pre-stretch, the higher the wrinkle wave number. The biaxially asymmetric pre-stretching thermally relaxed dielectric elastomer actuator is driven by an applied voltage. The larger stretch perpendicular to the stretching direction produces less deformation, and the smaller stretch parallel to the stretching direction produces less deformation. Larger deformation, resulting in asymmetric deformation.

3. Through the equal multiaxial pre-stretching thermal relaxation technology, a more uniform and thinner dielectric elastomer film can be prepared from a thick film, and the driving voltage of the obtained dielectric elastomer film can be driven within 0.05-5KV. The breakdown field strength of the obtained dielectric elastomer film is increased to 1-5 times of the original. At the same time, the driving performance of the dielectric elastomer driver is also improved to 1-5 times of the original. The greater the pre-stretching degree, the better the driving performance after thermal relaxation.

Description of drawings

Fig. 1 is the failure probability distribution diagram of the electric breakdown field strength of the dielectric elastomer film based on the Weber distribution analysis;

Fig. 2 is the probability density distribution diagram of analyzing the electric breakdown field strength of dielectric elastomer film based on Weber distribution;

FIG. 3 is a comparison diagram of the driving performance of the same thickness of the dielectric elastomer film used for the dielectric driver;

Fig. 4 is the electric driving effect diagram of the dielectric elastomer film with different degrees of uniaxial pre-stretching thermal relaxation, in the figure, (a) is the electric driving effect diagram of the initial film, (b) is the uniaxial 200% pre-stretching heat The electric driving effect diagram of the film after relaxation, (c) is the electric driving effect diagram of the film after uniaxial 400% pre-stretching thermal relaxation.

Detailed ways

The following are specific embodiments of the present invention to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

Example 1: Equal 4-axis pre-stretching thermal relaxation dielectric elastomer based on polystyrene-poly-n-butyl acrylate-polystyrene (molecular weight: 1.5W-12W-1.5W) triblock thermoplastic elastomer film Evaluation of Electric Breakdown Field Strength of Thin Films

The initial film (thickness of about 83 microns) of polystyrene-poly-n-butyl acrylate-polystyrene triblock thermoplastic elastomer was pre-stretched to 2 times the area of the original film (thickness about 44 μm) by equiaxes, respectively. micron), 3 times (thickness is about 26 microns), about 7 times (thickness is about 12 microns); under fixed pre-stretching conditions, put them in 115 ° C for thermal relaxation for 10 hours and then cool at room temperature. The electrical breakdown field strengths of the dielectric elastomer films obtained before and after pre-stretching thermal relaxation were compared with the Weber distribution. It can be seen from Figure 1 and Figure 2 that the greater the degree of pre-stretching of the film, the higher the electric breakdown field strength of the film obtained after thermal relaxation; the pre-stretched film is about twice the initial film area after thermal relaxation. , the electric breakdown field strength is about 1.3 times that of the initial film; the pre-stretched film is about 3 times the initial film area after thermal relaxation, the electric breakdown field strength is about 1.7 times that of the initial film; pre-stretching is the initial film. After thermal relaxation of the film with an area of about 7 times, the electric breakdown field strength is about 2.2 times that of the initial film; it can be seen that the greater the pre-stretching degree of the film, the higher the electric breakdown field of the film obtained after thermal relaxation powerful.

In Figures 1 and 2, 1, initial film; 2, pre-stretched to about 2 times the area of the initial film, the dielectric elastomer film obtained after thermal relaxation; 3, pre-stretched to about 3 times the area of the initial film , the dielectric elastomer film obtained after thermal relaxation; 4, the dielectric elastomer film obtained after pre-stretching to about 7 times the area of the initial film, after thermal relaxation.

Example 2: Equal 4-axis pre-stretching thermal relaxation dielectric elastomer based on polystyrene-poly-n-butyl acrylate-polystyrene (molecular weight: 1.5W-12W-1.5W) triblock thermoplastic elastomer film Driving performance test of thin films

The initial films of polystyrene-poly-n-butyl acrylate-polystyrene triblock thermoplastic elastomer (thickness of 200 microns, 100 microns, 50 microns, 25 microns, 12 microns) were pre-stretched by equiaxed 4 axes respectively Dielectric elastomer film with a thickness of 12 microns; under fixed pre-stretching conditions, placed in 115 °C for thermal relaxation for 10 hours and then cooled at room temperature. Then the same carbon nanotube flexible electrodes were coated on the upper and lower surfaces of the dielectric elastomer film for electrical driving tests. As shown in Fig. 3, the electrical breakdown voltage of the initial film with a thickness of 12 μm is about 450 V, the breakdown field strength is about 42.8 V/μm, and the maximum driving deformation is 11.7%; the initial film with a thickness of 25 μm is pre-stretched When stretched to 12 μm, the electrical breakdown voltage after thermal relaxation is about 475V, the breakdown field strength is about 46.9V/μm, and the maximum driving deformation is 13.1%; the initial film with a thickness of 50 μm is pre-stretched to 12 μm, The electrical breakdown voltage after thermal relaxation is about 500V, the breakdown field strength is about 49.4V/μm, and the maximum driving deformation is 12.4%; the initial film with a thickness of 100 μm is pre-stretched to 12 μm, and the electrical The breakdown voltage is about 650V, the breakdown field strength is about 62.1V/μm, and the maximum driving deformation is 14.0%; the initial film with a thickness of 25 μm is pre-stretched to 12 μm, and the electrical breakdown voltage after thermal relaxation is about 800V, the breakdown field strength is about 82.0V/μm, and the maximum driving deformation is 22.4%.

In Fig. 3, 1, the initial film; 2, the dielectric elastomer film obtained after pre-stretching to about 2 times the area of the initial film, after thermal relaxation; 3, pre-stretching to about 4 times the area of the initial film, thermal relaxation 4. Pre-stretched to about 8 times the area of the initial film, the dielectric elastomer film obtained after thermal relaxation; 5. Pre-stretched to about 16 times the area of the initial film, thermally relaxed The resulting dielectric elastomer film.

Example 3: Based on polystyrene-poly-n-butyl acrylate-polystyrene (molecular weight: 1.5W-12W-1.5W) triblock thermoplastic elastomer film after different degrees of uniaxial pre-stretching thermal relaxation Anisotropy drives performance

The initial film of polystyrene-poly-n-butyl acrylate-polystyrene triblock thermoplastic elastomer was pre-stretched uniaxially to 2 times and 4 times the length of the initial film respectively; After thermal relaxation at 110°C for 10 hours, it was cooled at room temperature. Then the same carbon nanotube flexible electrodes were coated on the upper and lower surfaces of the dielectric elastomer film for electrical driving tests. As shown in Fig. 4, the self-supporting frameless electric drive produces anisotropic deformation, and the initial film without pre-stretching treatment (as shown in Fig. 4(a)) has no obvious anisotropy when deformed by applied voltage Deformation: The thermally relaxed dielectric elastomer film (as shown in Figure 4(b)) pre-stretched by uniaxial 2 times, when driven by electricity, produces a large deformation perpendicular to the stretching direction, resulting in periodic wrinkling ; The thermally relaxed dielectric elastomer film (as shown in Figure 4(c)) was pre-stretched by 4 times uniaxially, resulting in more wrinkles.

Example 4: Iso-directional thermal relaxation of triblock thermoplastic elastomer film based on polystyrene-poly-n-butyl acrylate-polystyrene (molecular weight: 1.5W-12W-1.5W) after biaxial asymmetric pre-stretching Heterosexual drive performance

The initial film of polystyrene-poly-n-butyl acrylate-polystyrene triblock thermoplastic elastomer was biaxially asymmetrically pre-stretched, one side was pre-stretched to twice the length of the initial film, and the other side was pre-stretched stretched to 4 times the length of the initial film; under the condition of fixed pre-stretching, put it into thermal relaxation at 120 °C for 9 hours and then cooled at room temperature to obtain a self-supporting dielectric elastomer film without frame fixing. Then the same carbon nanotube flexible electrodes were coated on the upper and lower surfaces of the dielectric elastomer film for electrical driving tests. The biaxially asymmetric pre-stretching thermally relaxed dielectric elastomer actuator is driven by an applied voltage. The larger stretching degree parallel to the stretching direction produces less deformation, and the smaller stretching parallel to the stretching direction produces less deformation. Larger deformation, resulting in asymmetric deformation.

Claims (6)

1. a block copolymer thermoplastic dielectric elastomer film, is characterized in that, it is prepared by the following method: at first uniaxial pre-stretching, equal biaxial pre-stretching is carried out to the block copolymer thermoplastic dielectric elastomer , equal multiaxial pre-stretching or biaxial asymmetric pre-stretching; wherein, the degree of uniaxial pre-stretching is 1 to 20 times the initial area; the degree of equal biaxial pre-stretching and equal multi-axial pre-stretching is 1 to 30 times the initial area, and the stretching ratio of biaxial asymmetric pre-stretching is 1 to 400:20; Placed in a temperature range of 50 to 150 ° C for thermal relaxation for 0.5 to 20 hours to obtain a block copolymer thermoplastic dielectric elastomer film; the general structural formula of the block copolymer thermoplastic dielectric elastomer is A-B-A; wherein, A is selected from Homopolymer from styrene; B is n-butyl acrylate homopolymer, n-butyl methacrylate homopolymer, isobutyl methacrylate homopolymer, tert-butyl acrylate homopolymer, acrylic acid-2- Ethylhexyl homopolymer, ethyl acrylate homopolymer or copolymer of at least two monomers of butyl acrylate, n-butyl methacrylate, isobutyl methacrylate, isooctyl acrylate, ethyl acrylate . 2 . The block copolymer thermoplastic dielectric elastomer film according to claim 1 , wherein the method of maintaining the pre-stretching condition is to fix the block copolymer thermoplastic dielectric elastomer on a frame or a non-stick film. 3 . on the base. 3. The block copolymer thermoplastic dielectric elastomer film according to claim 1, wherein in the block copolymer thermoplastic dielectric elastomer, A is a hard segment, and B is a soft segment; the hard segment The glass transition temperature of the soft segment is greater than 50°C, and the glass transition temperature of the soft segment is less than -10°C. 4 . The block copolymer thermoplastic dielectric elastomer film according to claim 3 , wherein the total molecular weight of the block copolymer thermoplastic dielectric elastomer is 50,000 to 500,000, and the number average of the hard segments is 50,000. 5 . The molecular weight is 0.5 to 50,000, the number average molecular weight of the soft segment is 50,000 to 400,000, and the soft segment accounts for 60%-95% of the total weight of the block copolymer thermoplastic dielectric elastomer. 5. A dielectric actuator comprising the block copolymer thermoplastic dielectric elastomer film of claim 1, wherein the dielectric actuator consists of an upper electrode, a block copolymer thermoplastic dielectric elastomer film and a lower electrode connected in sequence. 6 . The dielectric driver according to claim 5 , wherein the upper electrode and the lower electrode are flexible electrodes selected from composite materials of carbon nanotubes, carbon paste, hydrogel, carbon powder and polymer. 7 .

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