A method for preparing a polyacrylate composite dielectric elastomer

Abstract

The application provides a preparation method of a polyacrylate composite dielectric elastomer, comprising the following steps: step 1, preparing a polyacrylate dielectric elastomer matrix prepolymer solution; step 2, synthesizing perovskite quantum dot powder with fluorescent properties; step 3, blending the polyacrylate dielectric elastomer matrix prepolymer solution with a perovskite quantum dot solution to obtain a perovskite-doped polyacrylate dielectric elastomer prepolymer solution; and step 4, dropping the perovskite-doped polyacrylate dielectric elastomer prepolymer solution onto a film preparation mold, and preparing a polyacrylate composite dielectric elastomer containing a multilayer perovskite-doped polyacrylate dielectric elastomer film through a wet lamination process under the condition of ultraviolet light irradiation. The polyacrylate composite dielectric elastomer prepared by the preparation method of the polyacrylate composite dielectric elastomer has excellent electrochromic properties and fluorescent properties.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of smart materials, in particular to a preparation method of a polyacrylate composite dielectric elastomer. BACKGROUND

[0002] Dielectric elastomer (DE) is a kind of polymer elastomer material with high dielectric constant, which can autonomously change volume and shape under the stimulation of an applied electric field, and convert electric energy output into mechanical energy. DE material is praised as a new generation of "artificial muscle" material due to its good flexibility, light weight, high energy density and other advantages, and has wide application prospects.

[0003] Currently, widely used dielectric elastomers include acrylate, polyurethane, silicone rubber and their composite materials, each type of dielectric elastomer has its unique performance advantages. Acrylate dielectric elastomer has high energy density and large in-plane strain; polyurethane dielectric elastomer has high dielectric constant; silicone rubber dielectric elastomer has low viscoelasticity and fast response. In order to prepare high-performance dielectric elastomers, acrylate materials with high strain and high energy density are usually the preferred materials. However, in the current research and application, the dielectric elastomer still needs to be improved in terms of electric drive efficiency, manufacturing process and multi-functional integration. For example, polyacrylic-based materials need to apply a high electric field, usually reaching the level of hundreds of megavolts per millimeter. In order to achieve the required high electric field strength, the conventional method is to produce extremely thin films, usually with a thickness of microns, which puts higher requirements on the production process of the film. Secondly, in order to pursue high energy output of the overall material device, the film is usually stacked, the flexible electrode is coated between the layers, the process of bonding each layer of film and integrating the device requires high process and low fault tolerance; in addition, the current dielectric elastomer has a single function, mainly for actuation. Therefore, in view of these limitations, a polyacrylate dielectric elastomer composite material with more excellent performance is needed. SUMMARY

[0004] The embodiments of the present application provide a preparation method of a polyacrylate composite dielectric elastomer to at least solve one of the problems in the related art. To achieve this purpose, the present application realizes the following technical scheme.

[0005] The embodiments of the present application provide a preparation method of a polyacrylate composite dielectric elastomer, comprising:

[0006] Step 1: preparing a polyacrylate dielectric elastomer matrix prepolymer solution;

[0007] Step 2: synthesizing perovskite quantum dot powder with fluorescent properties;

[0008] Step 3: dissolving the perovskite quantum dot powder to obtain a perovskite quantum dot solution, and blending the perovskite quantum dot solution with the polyacrylate dielectric elastomer base prepolymer under light-proof conditions to obtain a perovskite-doped polyacrylate dielectric elastomer prepolymer;

[0009] Step 4: dropping the perovskite-doped polyacrylate dielectric elastomer prepolymer onto a film preparation mold, and pre-curing under the condition of ultraviolet light irradiation to generate a first layer of perovskite-doped polyacrylate dielectric elastomer film;

[0010] Step 5: after the temperature of the first layer of perovskite-doped polyacrylate dielectric elastomer film cools to room temperature, dropping the perovskite-doped polyacrylate dielectric elastomer prepolymer onto the first layer of perovskite-doped polyacrylate dielectric elastomer film, and pre-curing under the condition of ultraviolet light irradiation to generate a second layer of perovskite-doped polyacrylate dielectric elastomer film;

[0011] Step 6: repeating the cooling to room temperature, dropping the perovskite-doped polyacrylate dielectric elastomer prepolymer, and ultraviolet light irradiation operations of Step 5 for the second layer of perovskite-doped polyacrylate dielectric elastomer film several times to obtain a polyacrylate composite dielectric elastomer comprising a multi-layer perovskite-doped polyacrylate dielectric elastomer film.

[0012] Further, 100 parts of n-butyl acrylate monomer is mixed with 30-80 parts of a bifunctional urethane acrylate compound and 0.5-2.5 parts of a 2-hydroxy-2-methylpropyl phenone (HMPP) photoinitiator to obtain the polyacrylate dielectric elastomer base prepolymer. That is, if the n-butyl acrylate concentration is taken as 100 wt.%, and the concentrations of the remaining reagents are calculated in proportion to this benchmark, then the concentration of the bifunctional urethane acrylate compound is 30-80 wt.%, and the concentration of the HMPP initiator is 0.5-2.5 wt.%.

[0013] Further, Step 2 includes: Step 21: dissolving 0.073-0.293 parts of lead bromide and 0.042-0.170 parts of cesium bromide in a dimethylamide solvent to form a perovskite precursor solution; Step 22: dropping the perovskite precursor solution into a toluene solvent, and stirring to cause a perovskite quantum dot precipitation reaction; and Step 23: adding an ethyl acetate solvent to the perovskite quantum dot mixed solution that precipitates, and purifying to collect the precipitate to obtain the perovskite quantum dot powder having fluorescence properties.

[0014] Further, step 21 comprises: dissolving 0.073-0.293 parts of lead bromide and 0.042-0.170 parts of cesium bromide in the dimethylamide solvent, ultrasonic dissolving and mixing with oleic acid and oleylamine as surfactants at 20-60℃ to form a uniform perovskite precursor solution. That is, if the n-butyl acrylate concentration is set as 100wt.%, the perovskite doped polyacrylate elastomer prepolymer solution prepared in step 3 has a doping concentration of perovskite quantum dots of 0.005-0.030wt.%.

[0015] Further, step 3 comprises: dissolving the perovskite quantum dot powder in n-hexane to obtain the perovskite quantum dot solution.

[0016] Further, the pre-curing conditions of ultraviolet irradiation in steps 4-6 comprise: a light source height of 10-30cm, an irradiation intensity of 64mW / cm 3 -320mW / cm 3 , and an irradiation time of 5-30 seconds.

[0017] Further, before step 4, there is also included: dropwise adding the polyacrylate elastomer base prepolymer solution prepared in step 1 to a film preparation mold, pre-curing under ultraviolet irradiation to generate a first layer of polyacrylate elastomer film, and then performing steps 4-6 on the first layer of polyacrylate elastomer film, i.e. forming the multi-layer perovskite doped polyacrylate elastomer film on the first layer of polyacrylate elastomer film; and after step 6, there is also included: dropwise adding the polyacrylate elastomer base prepolymer solution prepared in step 1 to the last layer of perovskite doped polyacrylate elastomer film, pre-curing under ultraviolet irradiation to generate a second layer of polyacrylate elastomer film, to finally obtain a sandwich structure of polyacrylate composite dielectric elastomer.

[0018] Further, the curing conditions of ultraviolet irradiation for preparing the first layer of polyacrylate elastomer film and the second layer of polyacrylate elastomer film comprise: a light source height of 10-30cm, an irradiation intensity of 64mW / cm 3 -320mW / cm 3 , and an irradiation time of 5-30 minutes.

[0019] Further, the polyacrylate dielectric elastomer prepared in step 6 is kept at a temperature of 20-60℃ for 8-16h to remove excess unreacted polymer monomers and solvents.

[0020] The embodiments of the present application have the following beneficial effects:

[0021] (1) The embodiment of the present application prepares a polyacrylate composite dielectric elastomer doped with fluorescent perovskite quantum dots (referred to as BAC@PQDs) through a series of preparation steps and processes such as synthesis of a polyacrylate (BAC) DE matrix, synthesis of perovskite quantum dots (PQDs), synthesis of a polyacrylate DE composite material doped with perovskite quantum dots, and wet preparation of a laminated structure. The composite dielectric elastomer has excellent electrochromic properties and fluorescent properties. For example, the prepared composite dielectric elastomer has an in-plane actuation strain rate of 120.34% under the drive of an electric field of 12 kV / mm, and under the condition of achieving the same actuation strain, the required drive electric field strength is reduced by 6-8 times relative to the pure polyacrylate DE matrix.

[0022] (2) The addition of perovskite quantum dots not only improves the electromechanical properties of the polyacrylate DE matrix, but also integrates excellent fluorescent function into the dielectric elastomer, which is of great significance for the development of multifunctional dielectric elastomer material research.

[0023] (3) Adjusting the doping concentration of perovskite quantum dots can maintain the actuation performance of the composite dielectric elastomer while maintaining its fluorescent properties.

[0024] (4) The embodiment of the present application improves the electromechanical properties of the prepared composite dielectric elastomer, such as dielectric loss, electrical breakdown strength, mechanical properties, and energy density and viscoelasticity, by using the wet method to prepare the laminated polyacrylate DE film, compared with the traditional method of stacking and bonding thin films and coating flexible electrodes between layers. Specifically, (a) the dielectric constant of the DE composite dielectric elastomer increases with the increase of the concentration of perovskite quantum dot particles, which is due to the increase of the overall polarization caused by the increase of the concentration of perovskite quantum dot particles. However, when the concentration of perovskite quantum dot particles increases, the dielectric loss of the composite dielectric elastomer also increases, and the energy conversion rate decreases, which is not conducive to improving the actuation performance of DE. However, the dielectric loss of the composite dielectric elastomer is significantly improved after using the laminated wet process; (b) with the increase of the concentration of perovskite quantum dot particles, the electrical breakdown strength of the composite dielectric elastomer gradually decreases, which is due to the increase of defects such as voids in the composite dielectric elastomer, and the accumulation of charges caused by the aggregation of particles between the particles, which easily causes material breakdown. However, the laminated composite dielectric elastomer BAC@PQDs prepared by using the laminated wet process has better anti-electrical breakdown effect than the single-layer BAC@PQDs; (c) the Young's modulus of BAC@PQDs increases significantly compared with pure BAC matrix. The increase of the Young's modulus not only leads to the increase of the strength of the composite DE material, but also affects the actuation performance. The nanoparticles PQDs in the composite dielectric elastomer play a role similar to physical crosslinking points, which limit the relative sliding between molecular chains, thereby reducing the elongation at break of the composite dielectric elastomer and increasing the Young's modulus of the composite dielectric elastomer. This effect makes the composite dielectric elastomer more hard and tough. After using the laminated wet process, the elongation at break of the composite dielectric elastomer increases and the Young's modulus decreases, thereby increasing the Maxwell force generated by the composite dielectric elastomer under the applied electric field, promoting the actuation performance of the dielectric elastomer, reducing the strength and stiffness of the overall composite material, and weakening the influence of perovskite quantum dot doping on the strength and stiffness of the composite dielectric elastomer; (d) through the comparative calculation of energy density, it is further proved that the laminated composite dielectric elastomer prepared by the embodiment of the present application has excellent energy density, which can reach 67.42kJ / m 3 , which is 108.76% higher than the performance of the composite material prepared by the traditional method, highlighting the significant effect of the wet laminated process in improving the energy density of the material; (e) viscoelasticity test shows that the actuation performance of the laminated composite dielectric elastomer prepared by the embodiment of the present application is lost by 26.8% after 105 cycles of load, which indicates that it has high viscoelasticity.

[0025] (5) The embodiment of the present application further combines the sandwich layer structure with the laminated wet process, uses pure polyacrylate dielectric elastomer film as the bottom and top film of the composite dielectric elastomer, so that the entire polyacrylate dielectric elastomer has higher anti-breakdown performance, thereby improving the maximum actuation strain rate of the overall dielectric elastomer; at the same time, the multilayer perovskite quantum dot doped polyacrylate dielectric elastomer film is used as the middle layer of the composite dielectric elastomer, so that it has fluorescence performance, and at the same time enhances the actuation performance of the composite dielectric elastomer.

[0026] (6) In the selection of materials for preparing the polyacrylate dielectric elastomer matrix, n-butyl acrylate is selected as monomer 1, and a bifunctional urethane acrylate compound is introduced as monomer 2 to regulate the cross-linked network and toughness of the polymer. The multi-polar functional groups in monomer 2 help to increase more interfacial polarization and improve the actuation performance of the composite dielectric elastomer. BRIEF DESCRIPTION OF DRAWINGS

[0027] The accompanying drawings, which form a part of the present application, are used to provide further understanding of the present application, and the illustrative embodiments of the present application and their description serve the purpose of explaining the present application, and do not constitute improper limitations on the present application.

[0028] Figure 1 The reaction formula of the polyacrylate DE matrix single polymer chain of the embodiment 1 of the present application;

[0029] Figure 2 The absorption and emission spectrum diagram of the PQDs particles synthesized at different temperatures (0℃, 20℃, 40℃, 60℃, 80℃);

[0030] Figure 3 The (a) absolute fluorescence quantum efficiency (b) fluorescence lifetime diagram of the PQDs particles;

[0031] Figure 4 The TEM image of the perovskite quantum dots synthesized at 40℃;

[0032] Figure 5 The (a) particle size distribution diagram (b) X-ray diffraction diagram of the PQDs particles synthesized at 40℃;

[0033] Figure 6 The (left) dielectric constant (right) dielectric loss trend diagram of the BAC matrix under different polar monomer concentrations;

[0034] Figure 7 The (left) dielectric constant (right) dielectric loss trend diagram of the dielectric elastomer under different doping particle concentrations;

[0035] Figure 8The figure (left) shows the trend of the electrical breakdown strength of DE matrix with different polar monomer concentrations, and the figure (right) shows the trend of the electrical breakdown strength of composite DE with different particle doping concentrations;

[0036] Figure 9 The figure (left) shows the stress-strain, (b) elongation at break, and (c) Young's modulus and yield strength column chart of BAC matrix (a) with different polar monomer concentrations.

[0037] Figure 10 The figure (left) shows the Fourier infrared spectra of BAC6 DE matrix material before and after curing, and the figure (right) shows the infrared spectra of BAC6 matrix and BAC6@2PQDs composite material before and after doping.

[0038] Figure 11 The figure (left) shows the stress-strain, (b) elongation at break, and (c) Young's modulus and yield strength column chart of BAC matrix (a) with different polar monomer concentrations.

[0039] Figure 12 The figure (a) shows the UV fluorescence absorption spectra of perovskite quantum dots with different doping particle concentrations, the figure (c) shows the UV fluorescence absorption spectra of perovskite quantum dots with a concentration of 0.02wt%, and the figures (b, d) show the UV fluorescence emission spectra of BAC6@2PQDs composite DE material. DETAILED DESCRIPTION

[0040] To make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the embodiments of the present application will be described in detail below with reference to the drawings. However, those skilled in the art can understand that in the embodiments of the present application, many technical details are proposed in order to make the readers better understand the present application. However, the technical solutions claimed by the present application can be realized even without these technical details and various changes and modifications based on the following embodiments. The division of the following embodiments is for the convenience of description, and should not constitute any limitation on the specific embodiments of the present application, and the embodiments can be combined and referred to each other without contradiction.

[0041] Embodiment 1

[0042] The embodiments of the present application provide a preparation method of a polyacrylate composite dielectric elastomer, which comprises the following steps.

[0043] Step 1: Preparation of polyacrylate dielectric elastomer matrix prepolymer solution.

[0044] In this embodiment, a polyacrylate dielectric elastomer matrix with excellent actuation performance is constructed by using a method of indirectly initiating radical polymerization with photosensitizer. n-Butyl acrylate is selected as monomer 1, and a bifunctional urethane acrylate compound, such as CN9021NS (a product model of Shanghai Juncai Material Co., Ltd.) with a flexible polyether glycol segment and an aliphatic diisocyanate segment, is introduced as monomer 2 to regulate the cross-linking network and toughness of the polymer. The multi-polar functional groups in monomer 2 help to increase more interfacial polarization, improving the actuation performance of the composite dielectric elastomer. Under the irradiation of 365 nm ultraviolet light, HMPP photoinitiator is used to trigger the radical polymerization reaction. The reaction formula of a single polymerization chain of the polyacrylate DE matrix is shown in Figure 1

[0045] Specifically, 30-80 wt. % (mass percentage) of CN9021NS monomer is poured into it, and then 100 wt. % of n-butyl acrylate monomer and 0.5-2.5 wt. % of HMPP photoinitiator are added dropwise with a pipette. In this embodiment, the concentration of n-butyl acrylate monomer is 100 wt. % (with the concentration of n-butyl acrylate as the basis, set to 100 wt. %, and the concentrations of the remaining reagents are calculated in proportion to this basis), the concentration of the bifunctional urethane acrylate compound is 30-80 wt. %, and the concentration of the HMPP initiator is 0.5-2.5 wt. %. A small magnet is added to the mixed reagents, and the mixed reagents are stirred uniformly by a magnetic stirrer for 30-60 min. Since a large number of bubbles are generated during mixing, the mixed reagents are placed in a vacuum box to extract excess residual bubbles, and the vacuum extraction time can be 2-15 min.

[0046] Step 2: Synthesis of perovskite quantum dot powder with fluorescent properties.

[0047] In this embodiment, a ligand-assisted reprecipitation method is used to synthesize perovskite quantum dot powder with high fluorescence efficiency. The synthesis process involves strict control of the synthesis temperature, and after optimization, it is found that perovskite quantum dot powder with good fluorescence performance is obtained at 0-80℃, and 20-60℃ is a better temperature range, and 40℃ is the best temperature. As the main starting material for the synthesis reaction, cesium bromide and lead bromide are selected, and dimethylformamide (DMF) is used as the solvent to dissolve them. Oleic acid and oleylamine are introduced as surfactants to form a perovskite precursor solution. The perovskite precursor solution is injected into the organic phase of toluene by rapid stirring to initiate the precipitation process of perovskite quantum dots in the organic phase. In order to improve the purity and stability of the quantum dots, ethyl acetate is used as the organic solvent in the purification stage. Finally, after centrifugal separation, perovskite quantum dots with excellent fluorescent properties are successfully prepared. The specific steps include the following.

[0048] ​Step 21: Dissolve 0.073-0.293 parts of lead bromide and 0.042-0.170 parts of cesium bromide in DMF solvent, with oleic acid and oleylamine as surfactants, ultrasonic dissolution mixing is carried out at 20-60°C (with 40°C as the optimal temperature) to ensure uniform mixing of the two, forming a uniform perovskite precursor solution.

[0049] Step 22: Drop the perovskite precursor solution into toluene solvent, and quickly stir to precipitate the perovskite quantum dots. Specifically, place the toluene-containing solvent on a hot magnetic stirrer at 45°C for preheating, add a small magnet to the solution in advance, slowly drop the perovskite precursor solution, and use high-speed magnetic stirring for 1 hour to promote the precipitation of perovskite quantum dots.

[0050] Step 23: Add ethyl acetate solvent to the precipitated perovskite quantum dot mixed solution for purification, and collect the precipitate to obtain perovskite quantum dot powder with fluorescent properties. Specifically, pour the precipitated quantum dot mixed solution into an ethyl acetate centrifuge tube, mix thoroughly, and then place it in a high-speed centrifuge at 9000 rpm for 3 minutes. Then, pour out the supernatant and collect the precipitate.

[0051] Step 3: Dissolve the perovskite quantum dot powder to obtain a perovskite quantum dot solution, and blend the perovskite quantum dot solution with the polyacrylate dielectric elastomer base prepolymer under light-proof conditions to obtain a perovskite-doped polyacrylate dielectric elastomer prepolymer.

[0052] In this embodiment, the preparation of CsPbBr3 quantum dots produces a yellow powdery product, which is dissolved and dispersed in an appropriate amount of n-hexane, for example by ultrasonic dissolution for 10 minutes, to obtain a CsPbBr3 quantum dot solution. N-hexane, as a non-polar organic solvent, has good solubility for CsPbBr3 quantum dots, and due to its volatile nature, it can be used to disperse CsPbBr3 quantum dots in the polyacrylate DE base prepolymer before synthesis. During the high-temperature synthesis and post-processing of organic synthesis, n-hexane gradually volatilizes, providing convenience for the synthesis process. The pre-prepared polyacrylate DE base is blended with the CsPbBr3 quantum dot solution, and the blending process is carried out under light-proof conditions, and the mixture is mixed uniformly using a stirring magnet on a magnetic stirrer for 30 minutes. The mixed perovskite-doped polyacrylate dielectric elastomer prepolymer is subjected to vacuum bubble removal treatment to remove the bubbles generated in the system.

[0053] Step 4: Drop the perovskite-doped polyacrylate dielectric elastomer prepolymer onto a film preparation mold (such as a teflon grooved mold), and pre-cure under ultraviolet light to form a first layer of perovskite-doped polyacrylate dielectric elastomer film.

[0054] Step 5: After the temperature of the first layer of perovskite-doped polyacrylate dielectric elastomer film is cooled to room temperature, the perovskite-doped polyacrylate dielectric elastomer prepolymer solution is added dropwise to the first layer of perovskite-doped polyacrylate dielectric elastomer film, and the second layer of perovskite-doped polyacrylate dielectric elastomer film is generated by pre-curing under the condition of ultraviolet light irradiation.

[0055] Step 6: Repeat the cooling to room temperature, adding the perovskite-doped polyacrylate dielectric elastomer prepolymer solution, and ultraviolet light irradiation operations of Step 5 several times for the second layer of perovskite-doped polyacrylate dielectric elastomer film to obtain a polyacrylate composite dielectric elastomer containing a multi-layer perovskite-doped polyacrylate dielectric elastomer film.

[0056] In this embodiment, the pre-curing conditions of ultraviolet light irradiation in Steps 4-6 include: light source height 10 cm-30 cm, light intensity 64 mW / cm 3 -320 mW / cm 3 , light time 5-30 seconds.

[0057] Finally, the prepared polyacrylate dielectric elastomer is placed in an oven at 20-60°C for 8-16 hours to remove excess unreacted polymer monomers and solvents.

[0058] Example 2

[0059] The difference between this embodiment and Example 1 is that this embodiment further designs a sandwiched layer structure, combines a layer-by-layer wet process, uses pure polyacrylate DE film as the bottom and top films of the composite dielectric elastomer, so that the entire polyacrylate dielectric elastomer has higher anti-breakdown performance to protect the overall dielectric elastomer and thus improve the maximum actuation strain rate of the overall dielectric elastomer; at the same time, uses a multi-layer perovskite quantum dot-doped polyacrylate DE film as the middle layer of the composite dielectric elastomer, so that it has fluorescent performance and at the same time enhances the actuation performance of the composite dielectric elastomer.

[0060] The specific method is the same as Steps 1-3 of Example 1, which will not be repeated here.

[0061] Step 4: The polyacrylate DE matrix prepolymer solution prepared in Step 1 is added dropwise to a teflon groove mold, and a first layer of polyacrylate dielectric elastomer film is generated by pre-curing under the condition of ultraviolet light irradiation. The curing conditions of ultraviolet light irradiation include: light source height 10 cm-30 cm, light intensity 64 mW / cm 3 -320 mW / cm 3 , light time 5-30 minutes.

[0062] Step 5: Drop the perovskite-doped polyacrylate dielectric elastomer prepolymer solution on the first layer of perovskite-doped polyacrylate DE film, and pre-cure under UV irradiation to form the first layer of perovskite-doped polyacrylate DE film. The pre-curing conditions under UV irradiation include: light source height 10 cm to 30 cm, light intensity 64 mW / cm 3 ~ 320 mW / cm 3 , light exposure time 5 to 30 seconds.

[0063] Step 6: After the temperature of the first layer of perovskite-doped polyacrylate DE film cools to room temperature, drop the perovskite-doped polyacrylate dielectric elastomer prepolymer solution onto the first layer of perovskite-doped polyacrylate DE film, and pre-cure under UV irradiation to form the second layer of perovskite-doped polyacrylate dielectric elastomer film. The UV irradiation conditions are the same as those in Step 5 of this embodiment.

[0064] Step 7: Repeat the cooling to room temperature, dropping the perovskite-doped polyacrylate dielectric elastomer prepolymer solution, and UV irradiation operations of Step 6 several times for the second layer of perovskite-doped polyacrylate DE film to obtain a layered structure containing multiple layers of perovskite-doped polyacrylate DE film.

[0065] Step 8: Drop the polyacrylate dielectric elastomer matrix prepolymer solution prepared in Step 1 onto the last layer of perovskite-doped polyacrylate dielectric elastomer film, and pre-cure under UV irradiation (light source height 10 cm to 30 cm, light intensity 64 mW / cm 3 ~ 320 mW / cm 3 , light exposure time 5 to 30 minutes) to form the second layer of polyacrylate dielectric elastomer film, and finally obtain a sandwich-structured polyacrylate composite dielectric elastomer.

[0066] The polyacrylate composite dielectric elastomer prepared by the preparation method of the polyacrylate composite dielectric elastomer provided in the embodiments of the present application, as well as the electromechanical properties, actuation performance, optical properties, and microstructure of the intermediate material and matrix material, are further characterized and tested to further study the excellent actuation performance and fluorescent performance of the composite dielectric elastomer prepared by the preparation method provided in the present application.

[0067] 1. Characterization of perovskite quantum dot particles

[0068] 1.1 Fluorescence performance test (UV fluorescence spectrum, fluorescence lifetime test, absolute fluorescence quantum efficiency)

[0069] In the preparation process, the synthesis temperature is changed to study the influence of temperature on the optical properties of perovskite quantum dots. Five temperature gradients are set during the experiment, which are 0℃, 20℃, 40℃, 60℃ and 80℃. The influence of synthesis temperature on fluorescence performance is analyzed by testing the ultraviolet fluorescence absorption, emission spectrum, absolute fluorescence quantum efficiency and fluorescence lifetime of perovskite quantum dots after synthesis. With the increase of temperature, the ultraviolet absorption and emission spectrum of PQDs particles show a red shift phenomenon towards long wavelength direction, that is, the characteristic peak or peak wavelength of the spectrum increases. This red shift is usually related to the size of the particles and is affected by the quantum size effect. In quantum dots, the confinement of electrons and holes in three-dimensional space leads to the occurrence of quantum confinement effect. When the size of quantum dots decreases, the energy state transition level changes, which leads to the red shift phenomenon of spectral characteristics, making larger quantum dots tend to exhibit more blue emission, and smaller quantum dots exhibit more red emission. The fluorescence quantum efficiency first increases and then decreases, and the absolute fluorescence quantum efficiency at 40℃ is the highest, which is 90.36%. Different synthesis temperatures may have a significant impact on the synthesis process and properties of quantum dots, which may affect the size and shape of quantum dots. In general, the increase of synthesis temperature tends to cause the increase of particle size, on the contrary, lower synthesis temperature tends to generate smaller particles. From the fitting fluorescence lifetime graph, it can be seen that the image fitted is the average time required for the excited state of the fluorescent substance to transition to the ground state during the fluorescence process. The data after fitting is 21.14ns, and the fluorescence lifetime of the particles shows that the prepared PQDs particles have high fluorescence stability. The specific test graph is shown in Figures 2-3 .

[0070] 1.2 Transmission electron microscopy (TEM) and particle size distribution test

[0071] Figure 4 The transmission electron microscopy (TEM) image of perovskite quantum dots synthesized at 40℃ is shown. The microstructure and dispersion state of PQDs particles are observed by TEM, and it is found that the prepared PQDs particles are uniformly distributed. Through the observation of the scale, the particle size of the synthesized particles is mainly distributed in the range of 10 to 15 nanometers.

[0072] 1.3 X-ray diffraction (XRD) test

[0073] Figure 5 The (a) particle size distribution and (b) X-ray diffraction pattern of PQDs particles synthesized at 40℃ are shown. From Figure 5 (a), it can be seen that the perovskite quantum dots synthesized at 40℃ have a particle size distribution of 87.2% in the range of 7-15nm. Figure 9(b) The X-ray diffraction pattern of the PQDs particles synthesized at 40°C shows characteristic peaks at 15.1°, 20.3°, 30.1°, 43.2° compared with the XRD pattern of the standard substance, especially the peak at 30.1° is sharp, indicating that the crystallinity of the sample is high. The quantum dots under high crystallinity indicate that the atoms or molecules in the crystal are very orderly arranged, and the ordering of the crystal lattice plane is strong. At the same time, there are impurity peaks at 12.4° and 37.3°, indicating that the crystal contains impurities and amorphous parts, which may be related to the preparation process of the quantum dots.

[0074] 2. Test of the dielectric elastomer matrix film

[0075] 2.1 Electromechanical properties (dielectric constant / loss, electrical breakdown strength, mechanical properties)

[0076] Figure 6 The figures show the change trend of the dielectric constant (εr) and dielectric loss (tan δ) of the dielectric elastomer BAC with different concentrations of polar monomers (i.e. monomer 2 CN9021NS in Example 1) in the frequency range of 1-107Hz. Figure 6 In the figures, the dielectric constant of DE gradually decreases with the increase of frequency at different concentrations of polar monomers. In the BAC matrix, the increase of the concentration of polar monomer CN9021NS in the BAC matrix polymerization system increases the dielectric constant of the BAC matrix, mainly because the dielectric property of the material at low frequency depends on the interfacial polarization. With further increase of the frequency, the interfacial polarization weakens, and the dipole polarization dominates.

[0077] Figure 8 (Left) The electrical breakdown strength of the dielectric elastomer BAC. It can be seen from Figure 8 (Left) that the higher the concentration of polar monomers, the higher the electrical breakdown strength of the DE matrix with the increase of the concentration of polar monomers. The slope shows an increasing trend first and then a decreasing trend. With the increase of the concentration of polar monomers, the polymerization generates longer chain and more compact network structure, and at this time the molecular weight of the polymer increases, so the electrical breakdown strength increases. After reaching the critical concentration (60%wt), many free chains of polar monomers appear in the DE material system, and the existing free segments cause local defects in the DE material, resulting in a decrease in the slope of the overall electrical breakdown strength of the DE material.

[0078] From Figure 9(a), (b) It can be seen that the increase of the concentration of polar groups in the DE matrix leads to the decrease of the tensile strain rate at different polar monomer concentrations. As indicated in the specific values in Table 1, the elastic modulus of the polymer system increases with the increase of the concentration, and the change rate of the elastic modulus increases first and then decreases. The maximum elongation at break of the DE material at 30wt% concentration reaches 1350.97%, and then the elongation decreases. When the concentration of polar monomers increases to 80wt%, the elongation at break of the DE material decreases to 720.27%, and the maximum elongation at break of BAC8 decreases by 46.7% compared with BAC3. When the concentration of polar monomers reaches 60wt%, the change rate of the elongation at break slows down, and the overall trend is downward. The columnar Figure 9 (c), Table 1 values, the elongation at break is negatively correlated with the yield strength and Young's modulus. As shown in the chart data, the yield strength of BAC8 increases by 33.3% compared with BAC3, and the Young's modulus increases by 31.3%, indicating that the increase of the concentration of polar monomers increases the strength of the DE material, but decreases the maximum elongation of the DE material. And with 60wt% concentration as the boundary, the yield strength increases slowly, similar to the sudden change of the elongation at break.

[0079]

[0080] Table 1: Mechanical properties of BAC6 matrix, single-layer BAC6@2.0PQDs composite DE, and optimized laminated BAC6@2.0PQDs composite DE

[0081] Table 2 describes the in-plane actuation strain rate values of BAC matrix at different electric field strengths and different polar monomer concentrations. It can be seen that the monomer concentration and electric field strength affect the actuation performance of the BAC matrix. From the single analysis of the electric field strength, it is found that the electric field strength has a promoting effect on the actuation performance of the BAC matrix. High driving electric field is accompanied by high actuation strain, and high electric field can generate higher Maxwell force in the BAC matrix, resulting in better actuation effect. With the increase of the concentration of polar monomers, the actuation performance gradually increases and then decreases, and the in-plane strain reaches the best value of 113.52% when the concentration is 60wt%. After the dielectric elastomer composite material is incorporated, the internal charge distribution of the material can be changed, thereby affecting the actuation characteristics of the material.

[0082]

[0083]

[0084] Table 2: In-plane actuation strain rate of BAC matrix at different electric field strengths and different polar monomer concentrations

[0085] 2.3 Optical performance (microscopic morphology and structure characterization)

[0086] The infrared spectra of the prepolymer solution and the cured BAC6 matrix DE material are shown in Figure Figure 10 (left) before and after UV curing, respectively. The infrared characteristic region (4000cm -1 - 1500cm -1 ) in the spectra mainly observes and analyzes the vibration and stretching of the functional groups in the molecule, and different functional groups will produce characteristic peaks at specific wave number positions. Figure 10 (left) shows that the characteristic absorption peaks of both before and after curing in the infrared characteristic region are basically the same, but there are differences in the fingerprint region (1500cm -1 - 500cm -1 ) between them. There is a strong absorption band at about 1404, which corresponds to the in-plane stretching vibration region of the C=C bond. By tracing its roots through the synthesis reaction, it is speculated that the main source may be related to the synthesis of monomers-n-butyl acrylate (BA), polar monomers (CN 9021NS), etc. At the same time, there are strong absorption bands at 978 and 808 in the spectrum, which correspond to the out-of-plane stretching vibration region of the C=C bond, which also confirms that the characteristic peaks change before and after curing. There is a strong absorption band between 1230cm -1 - 1020cm -1 , but the peak shapes are different. The peak shape of one is wider and the peak shape of the other is narrower before and after curing, indicating that the number of double bonds decreases sharply after UV curing, the number of C-C single bond groups increases significantly, and finally the C-C single bond occupies the main part of the chain. The disappearance of double bonds indicates that the curing reaction is complete, and the polymer system is crosslinked and cured completely.

[0087] 3. Test of composite dielectric elastomer film

[0088] 3.1 Electromechanical properties (dielectric constant / loss, electrical breakdown strength, mechanical properties)

[0089] Figure 7 Table 1 and Table 3 show the change trend of the dielectric constant (εr) and dielectric loss (tanδ) of the dielectric elastomer BAC@PQDs / laminated BAC@PQDs with frequency in the frequency range of 1-107Hz. Figure 7 ​At low frequencies, the dielectric loss of BAC@PQDs composite DE materials is mainly caused by the conduction loss of leakage current. The tan δ of BAC6 material is 0.08 at 103 Hz, while the tan δ of BAC6@2.0PQDs composite DE material is 0.51, which is increased by 637.5% compared with the pure matrix. After optimizing the lamination process, the tan δ of BAC6@2PQDs composite DE material is 0.32, which is decreased by 37.3% compared with the single-layer DE composite material. In summary, the dielectric constant of the DE composite material increases with the increase of the concentration of PQDs particles, which is due to the increase of the overall polarization caused by the increase of the particle concentration. However, when the particle concentration increases, the dielectric loss of the system also increases, which reduces the energy conversion rate, which is not conducive to improving the actuation performance of DE. After using the optimized lamination process, the dielectric loss of the composite dielectric elastomer is improved.

[0090]

[0091]

[0092] Table 3: Dielectric constant and dielectric loss of BAC6 matrix, single-layer BAC6@2.0PQDs composite DE, lamination BAC6@2.0PQDs composite DE

[0093] Figure 8 The right part of Table 4 corresponds to the electric breakdown strength of dielectric elastomer BAC@PQDs / lamination BAC@PQDs, respectively. Figure 8 The right part of Figure 6 shows the basic trend of the electric breakdown strength of composite DE with particle concentration. The electric breakdown strength Eb of pure matrix BAC6 is 22.12 kV / mm, and it gradually decreases with the increase of particle concentration. When the doping concentration is 0.03%wt, the electric breakdown strength decreases to 20.01 kV / mm, which is decreased by 9.6%. This shows that filling PQDs particles has a significant effect on the electric breakdown strength of BAC6. The breakdown strength of DE material decreases significantly after doping concentration of 0.02wt%. At this time, due to the increase of defects such as voids in the system, and the easy accumulation of electric charge caused by the aggregation of particles, the material is easy to break down. After the lamination process is optimized, the electric breakdown strength of single-layer BAC6@2.0PQDs composite DE after doping is only 20.75 kV / mm, which is decreased by 6.7% compared with BAC6 matrix. The composite DE material is more likely to break down after pre-stretching of DEA. After the lamination process is optimized, the electric breakdown strength of the whole BAC6@2.0PQDs composite DE material is enhanced, which is decreased by only 0.8% compared with before optimization, and the anti-electric breakdown effect of the composite DE material is enhanced.

[0094]

[0095] Table 4: Electric breakdown strength of BAC6 matrix, single-layer BAC6@2.0 PQDs composite DE, and stacked BAC6@2.0 PQDs composite DE

[0096] Figure 11 The tensile strain rate of the BAC@PQDs composite DE system gradually decreased after particle doping in (a), (b), and (c). A small amount of particle doping did not significantly affect the composite DE material. Compared to the maximum elongation of 823.29% of the pure matrix BAC6, particle doping reduced the maximum elongation of the composite DE material. The elongation at break of the BAC6@3.0 PQDs composite DE material with a doping concentration of 0.03% wt was 726.05%, which was 12.8% lower than that of the pure matrix BAC6. The stress yield phenomenon generated during the polymer stretching process was judged by the yield strength value. The yield strength of the pure matrix BAC6 was 271.56 kPa, and the yield strength of the BAC6@3.0 PQDs composite DE was 285.15 kPa, which increased by 5.1%. The Young's modulus had a significant impact on the composite DE material, which increased by 15.6% compared to the pure matrix. The increase in Young's modulus not only led to an increase in the strength of the composite DE material, but also affected the actuation performance. The nanoparticles PQDs played a role similar to physical cross-linking points in the composite material. These particles limited the relative sliding between molecular chains, thereby reducing the elongation at break of the material while increasing the modulus of the material. This effect made the dielectric elastomer stiffer and stronger, although the BAC matrix might have lower hardness and strength compared to the particles. Image data showed that the addition of a small amount of particles had little effect on the fracture toughness of the material. However, the aggregation of particles might promote the propagation of cracks, thereby adversely affecting the toughness and fracture resistance of the material. As shown in Table 3, the elongation at break of the composite material increased after optimization of the process. The elongation at break of the stacked composite DE (806.26%) increased by 4.71% compared to the single-layer composite DE material (769.97%). The Young's modulus value decreased to (50.63 kPa), and the stacked process reduced the modulus of the composite DE by 3.41%. The yield strength value also changed synchronously. It can be seen that the optimization of the process decreased the modulus of the composite DE, and the increase in the elongation at break had a positive effect on the composite DE material. As mentioned in the introduction, the reduction in modulus can increase the Maxwell force generated by the electric field in the composite DE material, thereby improving the actuation performance of the DE material. The introduction of semiconductor particles into the polymer matrix BAC6 will enhance the strength and stiffness of the composite material. However, the wet stacking process used to combine the polymer matrix with the BAC@PQDs composite DE material can reduce the strength and stiffness of the overall composite material, thereby reducing the effect of particle doping on the strength and stiffness of the composite DE material.

[0097] 3.2 Actuation performance (in-plane actuation strain rate)

[0098] Table 5, Table 6 show the in-plane actuation strain rate trend of BAC@PQDs / laminated BAC@PQDs composites doped with different concentrations of particles. The data shows that the maximum in-plane actuation strain rate of BAC@PQDs decreases as the concentration of QDs increases, but the actuation performance of the DE material improves at the same field strength. Particle doping improves the dielectric system of the BACA matrix, but dielectric breakdown occurs easily, leading to a decrease in the maximum actuation strain rate, which affects the energy density of the DE material. This phenomenon occurs due to changes in doping concentration, and the dielectric properties show concentration dependence. Low concentration doping can lead to different effects, while high concentration can cause changes in interaction. Compared to the pure matrix, the actuation performance improves in one step at low concentration doping, but the maximum electric field decreases due to the increase in particle doping concentration, resulting in a decrease in the maximum actuation strain rate. The overall actuation performance decreases, leading to defects in the BAC@PQDs material, resulting in lower electric breakdown strength.

[0099]

[0100] Table 5: In-plane actuation strain values of BAC@PQDs composites doped with different concentrations of particles

[0101]

[0102] Table 6: In-plane actuation strain of BAC6 matrix, single-layer BAC6@2PQDs, and laminated BAC6@2PQDs under different electric fields

[0103] The laminated process is used for the entire DE material, the top and bottom films use BAC matrix as the reinforcing layer to improve the electric breakdown strength of the overall composite dielectric elastomer, and the BAC@PQDs composite DE material is used as the intermediate dielectric layer to improve the actuation performance of the overall composite dielectric elastomer. The wet process is simple to prepare, and the effect of the process-optimized composite DE material on the actuation performance of the composite DE material is explored. As can be seen from Table 4, the actuation performance is improved overall on the basis of DE, and compared to the single-layer structure, the process optimization improves the breakdown resistance of the DE composite material, and the actuation performance is further improved compared to the matrix material. The electric actuation strain of the laminated BAC6@2PQDs composite DE material reaches 120.34% under an electric field of 12 kV / mm. Compared to the single-layer composite DE material, the actuation strain rate and maximum driving voltage under a field strength of 12 kV / mm are increased by 42.46% and 50%, respectively, and the actuation performance of the composite DE material is significantly improved. The sandwich layer wet stacking process used in process optimization balances the balance of fluorescence and actuation performance, the inner dielectric layer improves the dielectric performance, and the outer reinforcing layer enhances the overall breakdown resistance of the composite DE material.

[0104] 3.3 Optical properties (fluorescence properties)

[0105] From Figure 12 As can be seen from (a), there are differences in the UV fluorescence absorption spectra of perovskite quantum dots at different doping particle concentrations. The absorption intensity increases with increasing particle concentration, and a platform appears when the concentration increases to 0.015wt%. A strong absorption peak appears at 0.03wt%, and the intensity of the absorption peak increases with increasing quantum dot concentration. This is because more quantum dots at the same light path length will cause more light to be absorbed, so the intensity of the fluorescence absorption peak is usually positively correlated with the concentration of quantum dots. With the increase of concentration, the shape of the fluorescence absorption peak may change. At low concentration, the absorption peak may become wider, while at high concentration, the absorption peak may be relatively narrow and sharp, and red shift phenomenon may occur, which is due to the enhanced effect caused by interaction, such as self-aggregation clustering effect. From Figure 12 As can be seen from (c), (d), the UV emission spectrum of the perovskite quantum dot fluorescence emission composite material is consistent with the peak value of the emission spectrum of the particles, but the same emission spectrum does not mean that the structure and properties of the two are exactly the same. In fact, the spectral similarity is the result of multiple interactions in the material, including the interaction between the particles and the doped particles. The emission spectrum of the BAC6@2PQDs composite material after the particles and the doped particles is the same, indicating that there is some interaction or energy level coupling between the two. This coupling leads to changes in the energy level structure and affects the emission characteristics of the spectrum. This coupling enhancement causes the emission spectrum to show similar characteristics.

[0106] Although embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and alterations can be made thereto without departing from the principles and spirit of the present application, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a polyacrylate composite dielectric elastomer, characterized by, The application relates to a preparation method of a polyacrylate composite dielectric elastomer. Step 1: preparing a polyacrylate dielectric elastomer matrix prepolymer solution; Step 2: synthesizing perovskite quantum dot powder with fluorescent properties; Step 3: dissolving the perovskite quantum dot powder to obtain a perovskite quantum dot solution, and blending the polyacrylate dielectric elastomer matrix prepolymer solution with the perovskite quantum dot solution under light-proof conditions to prepare a perovskite-doped polyacrylate dielectric elastomer prepolymer solution; Step 4: dropping the perovskite-doped polyacrylate dielectric elastomer prepolymer solution onto a film preparation mold, and pre-solidifying under the condition of ultraviolet light irradiation to generate a first layer of perovskite-doped polyacrylate dielectric elastomer film; Step 5: after the temperature of the first layer of perovskite-doped polyacrylate dielectric elastomer film cools to room temperature, dropping the perovskite-doped polyacrylate dielectric elastomer prepolymer solution onto the first layer of perovskite-doped polyacrylate dielectric elastomer film, and pre-solidifying under the condition of ultraviolet light irradiation to generate a second layer of perovskite-doped polyacrylate dielectric elastomer film; Step 6: repeating the cooling to room temperature, dropping the perovskite-doped polyacrylate dielectric elastomer prepolymer solution and ultraviolet light irradiation operations of step 5 on the second layer of perovskite-doped polyacrylate dielectric elastomer film for several times to prepare a polyacrylate composite dielectric elastomer containing a multilayer perovskite-doped polyacrylate dielectric elastomer film.

2. The method for preparing the polyacrylate composite dielectric elastomer according to claim 1, characterized in that, Step 1 comprises: mixing 100 parts of n-butyl acrylate monomer with 30-80 parts of a bifunctional urethane acrylate compound and 0.5-2.5 parts of 2-hydroxy-2-methylbenzophenone photoinitiator to prepare the polyacrylate dielectric elastomer matrix prepolymer solution.

3. The method for preparing the polyacrylate composite dielectric elastomer according to claim 1, characterized in that, Step 2 comprises: Step 21: dissolving 0.073-0.293 parts of lead bromide and 0.042-0.170 parts of cesium bromide in a dimethylamide solvent to form a perovskite precursor solution; Step 22: dropping the perovskite precursor solution into a toluene solvent, and stirring to cause a perovskite quantum dot precipitation reaction; Step 23: adding ethyl acetate solvent to the precipitated perovskite quantum dot mixed solution for purification, and collecting the precipitate to obtain the perovskite quantum dot powder with fluorescent properties.

4. The method for preparing the polyacrylate composite dielectric elastomer according to claim 3, characterized in that, Step 21 comprises: dissolving 0.073-0.293 parts of lead bromide and 0.042-0.170 parts of cesium bromide in the dimethylamide solvent, and ultrasonically dissolving and mixing at 20-60 DEG C with oleic acid and oleylamine as surfactants to form the uniform perovskite precursor solution.

5. The method for preparing the polyacrylate composite dielectric elastomer according to claim 1, characterized in that, Step 3 comprises: dissolving the perovskite quantum dot powder in n-hexane solvent to obtain the perovskite quantum dot solution.

6. The method for preparing the polyacrylate composite dielectric elastomer according to claim 1, characterized in that, The pre-curing conditions of UV irradiation in steps 4-6 include: light source height 10 cm to 30 cm, light intensity 64 mW / cm 3 to 320 mW / cm 3 , irradiation time 5 to 30 seconds.

7. The method for preparing the polyacrylate composite dielectric elastomer according to claim 1, characterized in that, Before step 4, the polyacrylate dielectric elastomer matrix prepolymer solution prepared in step 1 is dropped onto a film preparation mold, and pre-solidified under the condition of ultraviolet light irradiation to generate a first layer of polyacrylate dielectric elastomer film, and then the operations of steps 4-6 are performed on the first layer of polyacrylate dielectric elastomer film, that is, the multilayer perovskite-doped polyacrylate dielectric elastomer film is formed on the first layer of polyacrylate dielectric elastomer film.

8. The method for preparing the polyacrylate composite dielectric elastomer according to claim 7, characterized in that, After step 6, further comprising: adding the polyacrylate dielectric elastomer matrix prepolymer droplets prepared in step 1 to the last layer of perovskite-doped polyacrylate dielectric elastomer film, and pre-curing under the condition of ultraviolet light irradiation to generate a second layer of polyacrylate dielectric elastomer film, to finally obtain a sandwich-structured polyacrylate composite dielectric elastomer.

9. The method for preparing the polyacrylate composite dielectric elastomer according to claim 8, characterized in that, The curing condition of the first layer of the polyacrylate dielectric elastomer film and the second layer of the polyacrylate dielectric elastomer film by ultraviolet light irradiation includes: light source height 10cm-30cm, light intensity 64mW / cm 3 -320mW / cm 3 , light time 5-30 minutes.

10. The method for preparing the polyacrylate composite dielectric elastomer according to claim 1, characterized in that, The polyacrylate dielectric elastomer prepared in step 6 is kept at a temperature of 20-60°C for 8-16 hours to remove excess unreacted polymer monomers and solvents.

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