An Ag@BN / PVDF composite film, its preparation method and application

Abstract

The present invention belongs to the technical field of composite materials, and particularly relates to an Ag@BN / PVDF composite film, a preparation method thereof and an application. Through the induction of Ag nanoparticles, the content of polar crystal forms of the PVDF matrix in the Ag@BN / PVDF composite film is effectively increased; in the Ag@BN hybrid filler, the Ag nanoparticles are uniformly loaded on the surface of BN nanosheets, and the Ag@BN tends to be arranged in parallel and separated from each other in the PVDF matrix, thereby avoiding the excessive agglomeration of Ag nanoparticles and enabling the Ag@BN hybrid filler to form a large number of micro-capacitor structures in the PVDF matrix, thus effectively increasing the dielectric constant of the obtained composite material and maintaining a low conductivity and dielectric loss factor; the Ag@BN hybrid filler can also effectively increase the thermal conductivity of the obtained composite material.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite materials, and particularly relates to an Ag@BN / PVDF composite material film, a preparation method thereof, and an application thereof. Background Art

[0002] As a functional polymer material, polyvinylidene fluoride (PVDF) has excellent piezoelectric, ferroelectric, pyroelectric properties and a relatively high dielectric constant, and has good mechanical strength, chemical stability and flexibility. Therefore, it has a wide range of applications in the fields of capacitors, sensors, triggers, actuators, electromechanical transducers, real-time monitoring, artificial muscles, etc. Under different preparation conditions, PVDF can form five crystal forms: α, β, γ, δ, and ε. Among them, the most studied are the non-polar α crystal form and the polar β and γ crystal forms. The chain conformation of the α crystal form of PVDF is TGTG', which does not have electrical functions such as piezoelectricity, ferroelectricity, and pyroelectricity, but it is the most stable and easiest crystal form to obtain; while the chain conformations of the β and γ crystal forms of PVDF are TTTT and T3GT3G' respectively, and they both have piezoelectric, ferroelectric and pyroelectric properties after polarization treatment. In particular, the β crystal form with an all-trans chain conformation has the most significant electrical effect. Therefore, people have been studying how to effectively transform the α crystal form of PVDF into polar crystal forms by various means.

[0003] Currently, the common methods for preparing PVDF films containing polar crystal forms include high-strain stretching, electrospinning, solution casting, and adding nano-fillers, etc. Adding nano-fillers is considered to be one of the most valuable methods due to its simple process, and seeking suitable nano-enhanced functional fillers is the key to this method. At the same time, there is still a large gap between the dielectric constant of PVDF and that of inorganic ceramic materials, and its own low thermal conductivity coefficient leads to the accumulation of heat during the use of PVDF as an electrical functional material. Therefore, how to effectively composite PVDF with nano-fillers to improve its dielectric constant and thermal conductivity performance is also an urgent problem to be solved. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an Ag@BN / PVDF composite material film, a preparation method thereof, and an application thereof. The Ag@BN / PVDF composite material film prepared by the present invention has good dielectric properties and thermal conductivity performance, and the content of polar crystal forms in its PVDF matrix is relatively high.

[0005] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0006] The present invention provides an Ag@BN / PVDF composite film, which comprises a polyvinylidene fluoride film and Ag@BN hybrid fillers arranged at intervals and oriented in the polyvinylidene fluoride film; the Ag@BN hybrid fillers comprise boron nitride nanosheets and silver nanoparticles loaded on the surfaces of the boron nitride nanosheets.

[0007] Preferably, the mass ratio of the boron nitride nanosheets to the silver nanoparticles is 0.5-2.5:1; the mass percentage of the Ag@BN hybrid fillers in the Ag@BN / PVDF composite film is 1-15%;

[0008] Preferably, the particle size of the silver nanoparticles is 10-200 nm; the sheet diameter of the boron nitride nanosheets is 1-5 μm, and the thickness is 50-400 nm.

[0009] The present invention also provides a preparation method of the Ag@BN / PVDF composite film according to the above technical solution, which comprises the following steps:

[0010] After mixing boron nitride nanosheets, soluble silver salt, reducing organic solvent and surfactant, microwave heat treatment, solid-liquid separation and drying are carried out in sequence to obtain Ag@BN hybrid fillers;

[0011] The suspension obtained by mixing the Ag@BN hybrid fillers, polyvinylidene fluoride and organic solvent is placed in a coagulation bath for precipitation to obtain a precipitate;

[0012] The precipitate is washed, dried and hot-pressed in sequence to obtain the Ag@BN / PVDF composite film.

[0013] Preferably, the soluble silver salt comprises silver nitrate; the mass ratio of the boron nitride nanosheets to silver nitrate is 0.5-2.5:1.57.

[0014] Preferably, the surfactant comprises polyvinylpyrrolidone.

[0015] Preferably, the mass ratio of the boron nitride nanosheets to the surfactant is (0.4-1.5):(0.4-1.5).

[0016] Preferably, the power of the microwave heat treatment is 500-1000 W; the time of the microwave heat treatment is 1-5 min.

[0017] Preferably, the temperature of the hot pressing is 180-220 °C, and the pressure is 18-22 MPa.

[0018] The present invention also provides an application of the Ag@BN / PVDF composite film described in the above technical solution or the Ag@BN / PVDF composite film prepared by the preparation method described in the above technical solution in the preparation of capacitors, sensors, triggers, drivers, electromechanical transducers, real-time monitors or artificial muscles.

[0019] The present invention provides an Ag@BN / PVDF composite film, which comprises a polyvinylidene fluoride film and Ag@BN hybrid fillers arranged at intervals in a directional manner in the polyvinylidene fluoride film; the Ag@BN hybrid fillers include boron nitride nanosheets and silver nanoparticles loaded on the surfaces of the boron nitride nanosheets. In the Ag@BN hybrid fillers, the Ag nanoparticles are uniformly distributed on the BN nanosheets, and the Ag@BN are arranged in parallel in the polyvinylidene fluoride film and separated from each other, thus avoiding the excessive aggregation of the Ag nanoparticles. The present invention uses the Ag@BN hybrid fillers as the functional fillers of the polyvinylidene fluoride film, effectively improves the content of the polar crystal form of the polyvinylidene fluoride film through the induction of the Ag nanoparticles, and the Ag@BN hybrid fillers can form a large number of micro-capacitor structures in the polyvinylidene fluoride film, thereby effectively improving the dielectric constant of the obtained composite material and maintaining a low conductivity and dielectric loss factor. The Ag@BN hybrid fillers can also effectively improve the thermal conductivity coefficient of the obtained composite material. Therefore, the Ag@BN / PVDF composite film is expected to be applied to the preparation fields such as capacitors, sensors, triggers, drivers, electromechanical transducers, real-time monitors or artificial muscles. Description of the Drawings

[0020] Figure 1 Scanning electron microscope images of the Ag@BN hybrid fillers prepared in Example 1 of the present invention at different magnifications;

[0021] Figure 2 Cross-sectional scanning electron microscope image of the Ag@BN / PVDF composite material prepared in Example 3 of the present invention;

[0022] Figure 3 Test result diagrams of the dielectric constant, dielectric loss factor and alternating current conductivity of the Ag@BN / PVDF composite materials prepared in Examples 3 and 6 of the present invention and the PVDF film of the comparative example;

[0023] Figure 4 XRD diagrams of the Ag@BN / PVDF composite materials prepared in Examples 1-6 of the present invention and the PVDF film of the comparative example;

[0024] Figure 5 Infrared test result diagrams of the Ag@BN / PVDF composite materials prepared in Examples 1-6 of the present invention and the PVDF film of the comparative example. Detailed Embodiments

[0025] The present invention provides an Ag@BN / PVDF composite film, which comprises a polyvinylidene fluoride film and Ag@BN hybrid fillers arranged in a directional and spaced manner in the polyvinylidene fluoride film; the Ag@BN hybrid fillers include boron nitride nanosheets and silver nanoparticles loaded on the surfaces of the boron nitride nanosheets.

[0026] The Ag@BN / PVDF composite film provided by the present invention comprises a polyvinylidene fluoride film. In the present invention, the mass percentage content of the polyvinylidene fluoride film in the Ag@BN / PVDF composite film is preferably 85-99%, and more preferably 88-92%.

[0027] The Ag@BN / PVDF composite film provided by the present invention comprises Ag@BN hybrid fillers that tend to be arranged in a directional and spaced manner in the polyvinylidene fluoride film. In the present invention, the mass percentage content of the Ag@BN hybrid fillers in the Ag@BN / PVDF composite film is preferably 1-15%, and more preferably 8-12%.

[0028] In the present invention, the Ag@BN hybrid fillers include boron nitride nanosheets and silver nanoparticles loaded on the surfaces of the boron nitride nanosheets; the mass ratio of the boron nitride nanosheets to the silver nanoparticles is preferably 0.5-2.5:1, and more preferably 0.8-1.5:1; the particle size of the silver nanoparticles is preferably 10-200 nm, and more preferably 50-100 nm; the sheet diameter of the boron nitride nanosheets is 1-5 μm, and more preferably 2-4 μm, and the thickness is preferably 50-400 nm, and more preferably 100-300 nm.

[0029] In the Ag@BN hybrid fillers, Ag nanoparticles are uniformly distributed on the BN nanosheets, and Ag@BN tends to be arranged in parallel and separated from each other in the polyvinylidene fluoride film, thereby avoiding excessive agglomeration of Ag nanoparticles. The present invention uses Ag@BN hybrid fillers as functional fillers for the polyvinylidene fluoride film, effectively improving the content of polar crystal forms of the polyvinylidene fluoride film through the induction of Ag nanoparticles. The Ag@BN hybrid fillers can form a large number of micro-capacitor structures in the polyvinylidene fluoride film, thereby effectively improving the dielectric constant of the obtained composite material and maintaining a low conductivity and dielectric loss factor. The Ag@BN hybrid fillers can also effectively improve the thermal conductivity coefficient of the obtained composite material. Therefore, the Ag@BN / PVDF composite film is expected to be applied in fields such as capacitors, sensors, triggers, drivers, electromechanical transducers, real-time monitoring, or artificial muscles.

[0030] The present invention also provides a preparation method for the Ag@BN / PVDF composite film described in the above technical solution, which comprises the following steps:

[0031] After mixing boron nitride nanosheets, soluble silver salt, reducing organic solvent and surfactant, microwave heat treatment, solid-liquid separation and drying are carried out in sequence to obtain Ag@BN hybrid filler;

[0032] The suspension obtained by mixing the Ag@BN hybrid filler, polyvinylidene fluoride and organic solvent is placed in a coagulation bath for precipitation to obtain a precipitate;

[0033] The precipitate is washed, dried and hot-pressed in sequence to obtain an Ag@BN / PVDF composite film.

[0034] In the present invention, after mixing boron nitride nanosheets, soluble silver salt, reducing organic solvent and surfactant, microwave heat treatment is carried out to obtain a mixture liquid of Ag@BN hybrid filler.

[0035] In the present invention, the soluble silver salt preferably includes silver nitrate; the mass ratio of the boron nitride nanosheets to silver nitrate is preferably 0.5-2.5:1.57, more preferably 0.6-2.4:1.57.

[0036] In the present invention, the surfactant preferably includes polyvinylpyrrolidone; the mass ratio of the boron nitride nanosheets to the surfactant is preferably (0.4-1.5):(0.4-1.5), more preferably (0.8-1.2):(0.8-1.2). The present invention controls the morphology of the obtained Ag nanoparticles through the surfactant.

[0037] In the present invention, the reducing organic solvent preferably includes N,N-dimethylformamide; the mass of the boron nitride nanosheets to the volume of the reducing organic solvent is preferably (0.4-1) g:(50-100) mL, more preferably (0.5-0.8) g:(60-90) mL.

[0038] In the present invention, the mixing of boron nitride nanosheets, soluble silver salt, reducing organic solvent and surfactant is preferably carried out by first mixing the boron nitride nanosheets and the reducing organic solvent for the first ultrasonic treatment to obtain a suspension; adding the surfactant to the suspension for the first stirring, and then adding the soluble silver salt for the second stirring and the second ultrasonic treatment in sequence to obtain a mixed suspension. In the present invention, the power of the first ultrasonic treatment is preferably 200 - 600 W, more preferably 300 - 400 W, the temperature is preferably room temperature, the time is preferably 40 - 120 min, more preferably 60 - 100 min. In the present invention, the rate of the first stirring is preferably 300 - 600 rpm, more preferably 400 - 500 rpm, the temperature is preferably room temperature, the time is preferably 3 - 10 min, more preferably 3 - 6 min. In the present invention, the rate of the second stirring is preferably 300 - 600 rpm, more preferably 400 - 500 rpm, the temperature is preferably room temperature, the time is preferably 5 - 30 min, more preferably 10 - 20 min. In the present invention, the power of the second ultrasonic treatment is preferably 200 - 600 W, more preferably 300 - 400 W, the temperature is preferably room temperature, the time is preferably 5 - 20 min, more preferably 5 - 15 min.

[0039] In the present invention, the power of the microwave heat treatment is preferably 500 - 1000 W, more preferably 600 - 900 W; the time of the microwave heat treatment is preferably 1 - 5 min, more preferably 2 - 3 min.

[0040] After obtaining the Ag@BN hybrid filler mixture liquid, the present invention separates the solid from the Ag@BN hybrid filler mixture liquid to obtain a solid.

[0041] In the present invention, the solid-liquid separation is preferably centrifugation; the rotation speed of the centrifugation is preferably 8000 - 14000 rpm, more preferably 10000 - 12000 rpm; the time of the centrifugation is preferably 5 - 15 min, more preferably 10 - 12 min.

[0042] Before drying, the present invention preferably washes the solid with water and ethanol in sequence; the washing is preferably centrifugal washing; the number of times of washing with water is preferably 2 - 3 times, more preferably 2 times; the number of times of washing with ethanol is preferably 1 - 2 times, more preferably 1 time; the rotation speed of the centrifugal washing is preferably 8000 - 14000 rpm, more preferably 10000 - 12000 rpm; the time of the centrifugal washing is preferably 5 - 15 min, more preferably 10 - 12 min.

[0043] After obtaining the solid, the present invention dries the solid to obtain the Ag@BN hybrid filler.

[0044] In the present invention, the drying temperature is preferably 60 - 70 °C, more preferably 60 °C; the drying time is preferably 10 - 12 h, more preferably 12 h; the drying is preferably vacuum drying; the pressure of the vacuum drying is preferably 0.1 - 0.2 MPa, more preferably 0.1 MPa.

[0045] After obtaining the Ag@BN hybrid filler, the present invention places the suspension obtained by mixing the Ag@BN hybrid filler, polyvinylidene fluoride and an organic solvent in a coagulation bath for precipitation to obtain a precipitate.

[0046] In the present invention, the organic solvent is preferably N,N - dimethylformamide; the mass ratio of polyvinylidene fluoride to the volume of the organic solvent is preferably (2.55 - 2.97) g : (40 - 60) mL, more preferably (2.55 - 2.97) g : (45 - 50) mL; the mass ratio of polyvinylidene fluoride to the Ag@BN hybrid filler is preferably (2.55 - 2.97) : (0.03 - 0.45), more preferably (2.64 - 2.76) : (0.24 - 0.36).

[0047] In the present invention, the mixing of the Ag@BN hybrid filler, polyvinylidene fluoride and an organic solvent preferably first mixes polyvinylidene fluoride and the organic solvent for a first stirring to completely dissolve the polyvinylidene fluoride to obtain a polyvinylidene fluoride solution; then mixes the Ag@BN hybrid filler and the polyvinylidene fluoride solution and sequentially performs a second stirring and ultrasonic treatment to obtain a suspension. In the present invention, the rate of the first stirring is preferably 300 - 600 rpm, more preferably 400 - 500 rpm, the temperature is preferably 80 - 85 °C, more preferably 85 °C, and the time is preferably 0.5 - 2 h, more preferably 1 - 2 h; the rate of the second stirring is preferably 300 - 600 rpm, more preferably 400 - 500 rpm, the temperature is preferably 80 - 85 °C, more preferably 85 °C, and the time is preferably 20 - 40 min, more preferably 30 min. In the present invention, the power of the ultrasonic treatment is preferably 200 - 600 W, more preferably 300 - 400 W, the temperature is preferably room temperature, and the time is preferably 5 - 20 min, more preferably 5 - 15 min.

[0048] In the present invention, the coagulation bath is preferably water, more preferably deionized water.

[0049] After obtaining the precipitate, the present invention washes the precipitate to obtain a washed precipitate.

[0050] In the present invention, the washing is preferably sequentially cleaning with water and ethanol; the number of times of cleaning with water is preferably 2 - 3 times, more preferably 3 times; the number of times of cleaning with ethanol is preferably 2 - 3 times, more preferably 2 times.

[0051] After obtaining the washed precipitate, the present invention dries the washed precipitate to obtain a dry precipitate.

[0052] In the present invention, the temperature of the drying is preferably 60 - 70 °C, more preferably 60 °C; the time of the drying is preferably 20 - 24 h, more preferably 24 h; the drying is preferably vacuum drying; the pressure of the vacuum drying is preferably 0.1 - 0.2 MPa, more preferably 0.1 MPa.

[0053] After obtaining the dry precipitate, the present invention hot-presses and shapes the dry precipitate to obtain an Ag@BN / PVDF composite film.

[0054] In the present invention, the temperature of the hot-pressing and shaping is preferably 180 - 220 °C, more preferably 180 - 200 °C, and the pressure is preferably 18 - 22 MPa, more preferably 20 MPa.

[0055] The present invention also provides the application of the Ag@BN / PVDF composite film described in the above technical solution or the Ag@BN / PVDF composite film prepared by the preparation method described in the above technical solution in the preparation of capacitors, sensors, triggers, drivers, electromechanical transducers, real-time monitors or artificial muscles.

[0056] The present invention has no special limitation on the application mode of the Ag@BN / PVDF composite film in the preparation of capacitors, sensors, triggers, drivers, electromechanical transducers, real-time monitors or artificial muscles, and the well-known application modes in the art can be adopted.

[0057] Next, the technical solutions in the present invention will be clearly and completely described in conjunction with the embodiments in the present invention, but they cannot be understood as a limitation on the protection scope of the present invention.

[0058] Example 1

[0059] Measure 70 mL of N,N-dimethylformamide (DMF) solvent and pour it into a wide-mouth bottle. Then add 0.6 g of boron nitride (BN) nanosheets and ultrasonically disperse them at 300 W for 60 min at room temperature to obtain a uniformly dispersed BN suspension. Then add 0.6 g of polyvinylpyrrolidone (PVP) and stir at 500 rpm for 5 min at room temperature. Then quickly add 0.95 g of silver nitrate (AgNO3) and stir at 500 rpm for 10 min at room temperature, and then ultrasonically disperse at 300 W for 10 min at room temperature to obtain a mixed suspension. Place the mixed suspension obtained in the above wide-mouth bottle into a microwave oven and heat it at 900 W for 2 min, then centrifuge at 12,000 rpm for 10 min. Wash and centrifuge twice with deionized water, and then wash and centrifuge once with absolute ethanol, each time centrifuging at 12,000 rpm for 10 min. The obtained sample is vacuum dried at 60 °C and 0.1 MPa for 12 h to obtain Ag@BN hybrid filler;

[0060] Measure 50 mL of DMF solvent and pour it into a wide-mouth bottle. Then add 2970 mg of PVDF particles and stir at 500 rpm for 60 min at 85 °C to completely dissolve PVDF in DMF. Then add 30 mg of Ag@BN hybrid filler powder to the above wide-mouth bottle, and then stir at 500 rpm for 30 min at 85 °C and ultrasonically disperse at 300 W for 10 min at room temperature to make the Ag@BN hybrid filler powder uniformly dispersed to form a suspension. Pour the above suspension quickly into the prepared deionized water for precipitation. The obtained precipitate is first washed 3 times with deionized water, then washed 2 times with absolute ethanol, and then vacuum dried at 60 °C and 0.1 MPa for 24 h. The dried sample is hot-pressed and formed under the conditions of a temperature of 180 °C and a pressure of 20 MPa to obtain an Ag@BN / PVDF composite film.

[0061] Example 2

[0062] The difference from Example 1 is that 2850 mg of PVDF particles and 150 mg of the Ag@BN hybrid filler powder prepared in Example 1 are used to prepare the Ag@BN / PVDF composite film, and the rest of the content is the same as that in Example 1.

[0063] Example 3

[0064] The difference from Example 1 is that 2700 mg of PVDF particles and 300 mg of the Ag@BN hybrid filler powder prepared in Example 1 are used to prepare the Ag@BN / PVDF composite film, and the rest of the content is the same as that in Example 1.

[0065] Example 4

[0066] Measure 70 mL of N,N-dimethylformamide (DMF) solvent and pour it into a wide-mouth bottle. Then add 0.9 g of boron nitride (BN) nanosheets and ultrasonically disperse them at 300 W for 60 min at room temperature to obtain a uniformly dispersed BN suspension; then add 0.9 g of polyvinylpyrrolidone (PVP) and stir at 500 rpm for 5 min at room temperature, then quickly add 0.95 g of silver nitrate (AgNO3) and stir at 500 rpm for 10 min at room temperature, and then ultrasonically disperse at 300 W for 10 min at room temperature to obtain a mixed suspension; put the mixed suspension obtained in the above wide-mouth bottle into a microwave oven and heat it at 900 W for 2 min, then centrifuge at 12,000 rpm for 10 min, wash with deionized water and centrifuge 2 times, then wash with absolute ethanol and centrifuge 1 time, centrifuge at 12,000 rpm for 10 min each time, and vacuum dry the obtained sample at 60 °C and 0.1 MPa for 12 h to obtain Ag@BN hybrid filler;

[0067] Measure 50 mL of DMF solvent and pour it into a wide-mouth bottle, then add 2970 mg of PVDF particles, and then stir at 500 rpm for 60 min at 85 °C to completely dissolve PVDF in DMF; then add 30 mg of Ag@BN hybrid filler powder to the above wide-mouth bottle, and then stir at 500 rpm for 30 min at 85 °C and ultrasonically disperse at 300 W for 10 min at room temperature to uniformly disperse the Ag@BN hybrid filler powder to form a suspension; quickly pour the above suspension into the prepared deionized water for precipitation; wash the obtained precipitate 3 times with deionized water, then wash 2 times with absolute ethanol, and then vacuum dry at 60 °C and 0.1 MPa for 24 h, and hot press the dried sample at a temperature of 180 °C and a pressure of 20 MPa to obtain an Ag@BN / PVDF composite film.

[0068] Example 5

[0069] The difference from Example 4 is that 2850 mg of PVDF particles and 150 mg of the Ag@BN hybrid filler powder prepared in Example 4 are used to prepare the Ag@BN / PVDF composite film, and the rest of the content is the same as that in Example 1.

[0070] Example 6

[0071] The difference from Example 4 is that 2700 mg of PVDF particles and 300 mg of the Ag@BN hybrid filler powder prepared in Example 4 are used to prepare the Ag@BN / PVDF composite film, and the rest of the content is the same as that in Example 4.

[0072] Comparative Example

[0073] 3 g of PVDF was hot-pressed at a temperature of 180 °C and a pressure of 20 MPa to obtain a PVDF film.

[0074] Performance testing

[0075] (1) The Ag@BN hybrid filler prepared in Example 1 was scanned by electron microscopy at different magnifications, and the results are as Figure 1 shown, where (a) is an electron micrograph at a magnification of 10k, and (b) is an electron micrograph at a magnification of 25k.

[0076] It can be seen from Figure 1 that the nano-Ag particles prepared by the rapid one-step microwave method are in-situ loaded on the surface of BN nanosheets. The Ag particles are relatively evenly distributed and no serious agglomeration phenomenon occurs. The well-insulating BN nanosheets effectively block the formation of the conductive path of Ag nanoparticles, thus proving the successful preparation of the Ag@BN hybrid filler.

[0077] (2) The cross-sectional scanning electron micrograph of the Ag@BN / PVDF composite material prepared in Example 3 is as Figure 2 shown.

[0078] It can be seen from Figure 2 that the Ag@BN hybrid filler is relatively evenly distributed in the PVDF matrix. And due to the hot-pressing effect during the preparation process, the Ag@BN hybrid fillers tend to be arranged parallel to each other separately, thus forming a large number of micro-capacitor structures in the PVDF matrix, which is beneficial to improving the dielectric constant of the composite material.

[0079] (3) The test results of the dielectric constant, dielectric loss factor and alternating current conductivity of the Ag@BN / PVDF composite materials prepared in Example 3 and Example 6 and the PVDF film of the comparative example are respectively as Figure 3 shown in (a), (b) and (c).

[0080] It can be seen from Figure 3As can be seen from (a), (b), and (c) in the figure: The addition of Ag@BN hybrid fillers can increase the dielectric constant of the resulting composite materials, and there is no significant increase in the dielectric loss factor and the alternating current conductivity. At a frequency of 100 Hz, the dielectric constants and dielectric loss factors of the Ag@BN / PVDF composite materials prepared in Example 3 and Example 6 are 15.4 and 0.042, and 9.3 and 0.039 respectively, while the corresponding values of the PVDF film in the comparative example are 8.6 and 0.055; at a frequency of 1000 Hz, the dielectric constants and dielectric loss factors of the Ag@BN / PVDF composite materials prepared in Example 3 and Example 6 are 15.0 and 0.023, and 8.9 and 0.021 respectively, while the corresponding values of the PVDF film in Comparative Example 1 are 8.2 and 0.024. This result shows that: The micro-capacitor structure formed by Ag@BN hybrid fillers can significantly increase the dielectric constant of the resulting composite materials; at the same time, since Ag nanoparticles are uniformly loaded on BN nanosheets, and the well-insulating BN nanosheets are separated from each other and arranged in parallel, the aggregation and mutual contact of Ag nanoparticles are avoided, so an effective conductive path cannot be formed, resulting in a low alternating current conductivity and dielectric loss factor of the resulting composite materials.

[0081] (4) The X-ray diffraction test results of the Ag@BN / PVDF composite materials prepared in Examples 1 to 6 and the PVDF film in the comparative example are as Figure 4 shown.

[0082] As can be Figure 4 seen: The addition of Ag@BN hybrid fillers can effectively increase the content of polar crystal forms in the PVDF matrix of the resulting composite materials. The main reason is that the presence of nano-Ag particles can induce a large number of non-polar α crystal forms into polar β and γ crystal forms.

[0083] (5) The infrared test results of the Ag@BN / PVDF composite materials prepared in Examples 1 to 6 and the PVDF film in the comparative example are as Figure 5 shown.

[0084] As can be Figure 5 seen, the infrared test results of the Ag@BN / PVDF composite materials prepared in Examples 1 to 6 and the PVDF film in the comparative example are consistent with the results of the above X-ray diffraction test, further indicating that the presence of Ag@BN hybrid fillers can effectively induce the formation of polar crystal forms in the PVDF matrix. Equation (1) can be used to calculate the content of polar crystal forms [F(polar)] of PVDF, where A 840 and A 764 are the absorption intensities of the sample at 840 cm -1 and 764 cm -1 respectively.

[0085]

[0086] It can be seen from the calculation results that the polar crystal form contents of Example 3, Example 6 and the comparative example are 71.2%, 72.6% and 26.0% respectively.

[0087] (6) It can be seen from the thermal conductivity test results that the thermal conductivity coefficients of Example 3, Example 6 and the comparative example are 0.31 W / m·K, 0.22 W / m·K and 0.12 W / m·K respectively, indicating that the addition of Ag@BN hybrid fillers can effectively improve the heat transfer ability of the obtained composite materials.

[0088] Therefore, the Ag@BN / PVDF composite material prepared by the present invention has the advantages of a relatively high polar crystal form content, dielectric constant, and thermal conductivity coefficient of the PVDF matrix, and relatively low dielectric loss factor and alternating current conductivity, and is expected to be applied in the field of electrofunctional polymer-based composite materials.

[0089] Although the above embodiments have described the present invention in detail, they are only a part rather than all of the embodiments of the present invention. People can also obtain other embodiments based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. An Ag@BN / PVDF composite film, characterized in that, It includes a polyvinylidene fluoride film and Ag@BN hybrid fillers arranged in a directional and spaced manner in the polyvinylidene fluoride film; the Ag@BN hybrid fillers include boron nitride nanosheets and silver nanoparticles loaded on the surface of the boron nitride nanosheets; The mass ratio of the boron nitride nanosheets to the silver nanoparticles is 0.8 - 1.5:1; the mass percentage content of the Ag@BN hybrid fillers in the Ag@BN / PVDF composite film is 1 - 15%; The particle size of the silver nanoparticles is 10 - 200 nm; the sheet diameter of the boron nitride nanosheets is 1 - 5 μm, and the thickness is 50 - 400 nm.

2. The preparation method of the Ag@BN / PVDF composite film according to claim 1, characterized in that, It includes the following steps: After mixing boron nitride nanosheets, soluble silver salt, reducing organic solvent and surfactant, successively carry out microwave heat treatment, solid-liquid separation and drying to obtain Ag@BN hybrid fillers; Place the suspension obtained by mixing the Ag@BN hybrid fillers, polyvinylidene fluoride and organic solvent in a coagulation bath for precipitation to obtain a precipitate; Wash, dry and hot press the precipitate in sequence to obtain the Ag@BN / PVDF composite film.

3. The preparation method according to claim 2, wherein The soluble silver salt includes silver nitrate; the mass ratio of the boron nitride nanosheets to silver nitrate is 0.5 - 2.5:1.

57.

4. The preparation method according to claim 2, wherein The surfactant includes polyvinylpyrrolidone.

5. The preparation method according to claim 2 or 4, characterized in that, The mass ratio of the boron nitride nanosheets to the surfactant is (0.4 - 1.5):(0.4 - 1.5).

6. The preparation method according to claim 2, wherein The power of the microwave heat treatment is 500 - 1000 W; the time of the microwave heat treatment is 1 - 5 min.

7. The preparation method according to claim 2, characterized in that, The temperature of the hot pressing is 180 - 220 °C, and the pressure is 18 - 22 MPa.

8. Application of the Ag@BN / PVDF composite film described in claim 1 or the Ag@BN / PVDF composite film prepared by the preparation method described in any one of claims 2 - 7 in the preparation of capacitors, sensors, triggers, drivers, electromechanical transducers, real-time monitors or artificial muscles.

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