Micro-nano composite electret film for micro energy collection and manufacturing method thereof

Abstract

The application discloses a micro-nano composite electret film for micro energy collection and a manufacturing method thereof. The application prepares a nano-particle dispersion liquid through ultrasonic technology or magnetic stirring technology, realizes the composite film of the micro-porous fiber and the nano-particle through spraying, evaporation, vacuum extraction and other methods, realizes the bonding of the composite micro-porous fiber and nano-particle film and the dense polymer of the top layer and the bottom layer through the method of hot pressing, and prepares the sandwich electret film of the composite micro-porous fiber and nano-particle through the action of a high-voltage electric field. The application can improve the surface potential of the electret film, increase the interface defects of the middle layer, provide more charge storage space, and improve the stability of the charge. The micro-nano composite electret film has high surface potential and good stability. Through the electrostatic induction principle, the application has application prospects in the fields of micro electrostatic generators and active sensors.

Description

Technical Field

[0001] This invention belongs to the field of sensing and micro-energy harvesting, and specifically relates to a micro-nano composite electret thin film for micro-energy harvesting and its fabrication method. Background Technology

[0002] With the development of electret-related applications, electret thin films, based on the principle of electrostatic induction, have rapidly developed in fields such as wearable active sensors and micro-generators. However, traditional methods for preparing electret thin films struggle to achieve high surface potential and high stability within a limited area and thickness, hindering their development in micro-electrostatic generators.

[0003] Currently, the common method for preparing electret films involves electreting a single-layer polymer film. However, this method has some drawbacks, such as unstable performance and easy failure of surface charge. One publicly disclosed patent for electret film preparation is "CN 107663276A," which proposes a "nano-ionic-polymer composite electret film." This patent mainly describes a method for forming a film using a mixed solution of nanoparticle dispersion and polymer dispersion, which can be applied to the fabrication of triboelectric generators. This patent is a dispersion-based film-forming technique and does not specifically address the effect of surface morphology on the discharge performance. In contrast, this patent is based on a microporous electretable polymer film (with a fibrous interwoven surface) mixed with micro / nano particles, aiming to increase its surface area, increase the effective area during discharge, and improve its charge stability. Patent "CN 107469466A" mainly proposes a microfiber / nanofiber composite electret filter material. This material is obtained through electrospinning, resulting in a filter material that combines microfibers and nanofibers. This composite fiber material ultimately achieves better charge storage capacity. The difference between this patent and the previous patent lies in their processes: the previous patent only uses electrospinning to ultimately form a composite fiber layer at the micron and nanoscale. This patent differs in that it introduces other processes to add additional nanoparticles between the fibers. These nanoparticles can adhere to the surface of the fiber material, further enhancing its surface area. Patent "CN105944455A" mainly proposes a method for preparing a multilayer spunbond electret filter material containing an energy-enhancing agent. Through the addition of the energy-enhancing agent and a specific multilayer composite structure, the resulting product can achieve higher filtration efficiency. In contrast, this patent introduces other particulate micro / nano materials on top of a fiber network structure, further enriching its surface and internal microstructure. Patent "CN 112428651 A" proposes an electret composite film, which is mainly composed of an organic functional film and a polymer film, divided into upper, middle, and lower layers, formed by hot pressing. The innovation of this patent differs from the previous one in that this paper proposes a method of mixing micro / nano particles in the middle layer, giving the film better charge storage capacity. Unlike the organic functional film in this patent.

[0004] While the existing patents mentioned above involve composite work of micro and nano structures, there are no reports on sandwich structures with nanoparticles and microporous fibers as the intermediate layer, and there are no mature technologies and methods for their preparation and application. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a micro-nano composite electret thin film for micro-energy harvesting and its fabrication method. In particular, a sandwich electret thin film of composite microporous fibers and nanoparticles is formed by spraying and hot pressing, which can form an electret thin film with high surface potential.

[0006] This invention proposes a "rich inner microstructure + sandwich structure" approach, providing a sandwich electret film composed of composite microporous fibers and nanoparticles for micro-energy harvesting. It mainly comprises a three-layer structure: a first layer of dense electret-capable polymer film, a second layer of composite microporous fiber and nanoparticle film, and a third layer of dense electret-capable polymer film. This sandwich electret film offers advantages such as high surface potential and high charge stability.

[0007] The rich inner surface microstructure enhances the effective surface area during corona discharge, thereby increasing the surface potential of the sandwich electret film composed of composite microporous fibers and nanoparticles. Secondly, the sandwich film structure formed after hot pressing increases the interfacial defects (dense film / composite microporous fiber and nanoparticle interface), providing more charge storage space. Finally, the outermost dense film exhibits good hydrophobicity, improving charge stability. Based on the principle of electrostatic induction, this type of sandwich electret film can effectively improve its performance in sensors and micro-energy harvesters.

[0008] The method for fabricating micro / nano composite electret thin films for micro-energy harvesting of the present invention includes the following steps: 1) The nanoparticle dispersion is uniformly dispersed in a deionized aqueous solvent and stirred magnetically or ultrasonically. If heating is required, it is placed in a water bath at 30℃~100℃ to finally prepare a uniform and stable low-concentration nanoparticle dispersion with a mass percentage of 10%~40%.

[0009] 2) Fabrication of composite microporous fiber and nanoparticle films: A prepared low-concentration nanoparticle dispersion is loaded into the solution chamber of an airbrush. In a fume hood, a layer of the nanoparticle dispersion is sprayed onto the surface of the microporous fiber film using a spraying method. The air pressure of the airbrush propels the nanoparticles into the interfiber spaces of the microporous fiber film. After spraying, the microporous fiber film is dried in a 60°C oven. The same steps are then repeated on the back side of the microporous fiber film. This double-sided spraying and drying process is repeated 3-5 times to finally obtain the composite microporous fiber and nanoparticle film.

[0010] 3) Fabrication of a sandwich film of composite microporous fibers and nanoparticles: First, the dense electret polymer film is ultrasonically cleaned and then dried in a 60°C oven. Next, the three layers are stacked in the following order from top to bottom: dense electret polymer film, composite microporous fiber and nanoparticle film, and dense electret polymer film. The stacked three-layer film is sandwiched between two layers of highly heat-resistant polyimide film (to prevent contamination of the heating table during hot pressing). Then, the above five layers of film are placed on the heating table, and appropriate weights (3 MPa~10 MPa) are placed on them. The film is hot-pressed for 10~30 min to form a sandwich film of composite microporous fibers and nanoparticles.

[0011] 4) Fabrication of sandwich electret films using corona discharge: A sandwich film of composite microporous fibers and nanoparticles is attached to the lower electrode plate of a corona discharge device. Under conditions of relative humidity (RH) of 40–55%, a voltage of -10 kV to -18 kV is applied to the tip of a needle using an intermittent DC voltage application method with a duty cycle of 0.1–1. The distance between the needle tip and the lower electrode is 0.1–5 cm. Discharge is carried out for 1–10 minutes at a suitable temperature (room temperature), ultimately obtaining a sandwich electret film of composite microporous fibers and nanoparticles, i.e., a micro-nano composite electret film. During discharge, the air gap between the electrodes is broken down by the electric field, causing air ionization. Charges are trapped inside the film under the influence of the electric field. At the optimal discharge temperature of the film, the intermittent DC voltage application method with a certain duty cycle is beneficial for the charge injected into the shallow traps to escape due to thermal excitation and be recaptured by deeper traps under the influence of the electret's own field, thereby improving charge stability.

[0012] Optionally, according to the manufacturing method of the present invention, the nanoparticles are made of one of polytetrafluoroethylene (PTFE), fluorinated ethylene propylene copolymer, polypropylene, perfluoroethylene propylene, soluble polytetrafluoroethylene, polyvinylidene fluoride, and silicon dioxide, and have a particle size of 0.01~500 nm.

[0013] Optionally, according to the manufacturing method of the present invention, the magnetic stirring or ultrasonic stirring operation involved in the uniform dispersion step is as follows: the dispersion is magnetically stirred at room temperature for 10-30 min, or ultrasonically stirred for 10-30 min at a temperature of 30-50°C and a power of 60-100 W.

[0014] Optionally, the material of the microporous fiber membrane is one of electret microporous polytetrafluoroethylene (PTFE), fluorinated ethylene propylene copolymer, polypropylene, perfluoroethylene propylene, soluble polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl butyral, polystyrene, polyester, polyvinyl acetate, nylon 6, nylon 66, polyvinyl alcohol, polymethyl methacrylate, polyaniline, polyethylene oxide, polyvinylpyrrolidone, polyacrylonitrile, polycaprolactone, polyethylene terephthalate, polytetrafluoroethylene, polyethylene glycol, polyurethane, polysulfone, polyethersulfone, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-tetrafluoroethylene-perfluoromethyl vinyl ether, and polyvinylidene fluoride-trifluorochloroethylene, wherein the micropore size formed by its fiber structure is 0.02~3 mm.

[0015] Optionally, the dense electret polymer film is made of one of the following materials: polytetrafluoroethylene, fluorinated ethylene propylene copolymer, soluble polytetrafluoroethylene, polychlorotrifluorohexene, ethylene tetrafluoroethylene copolymer, perfluoropolymer, polyvinylidene fluoride, polyvinylidene fluoride trifluoroethylene copolymer, polypropylene, polyimide, polyethylene terephthalate, polyethylene, and cyclohexene copolymer, with a thickness of 0.01~0.1 mm.

[0016] Optionally, according to the manufacturing method of the present invention, in addition to spraying, the composite microporous fibers and nanoparticles can also be produced by vacuuming: that is, the microporous fiber film is placed in the nanoparticle dispersion, then placed in a vacuum chamber, and vacuumed for 10-20 minutes. During this process, the air in the microporous fiber film is expelled, which will draw in the nanoparticles from the dispersion. Finally, the microporous fiber film is taken out and placed in an oven to dry. Drying can also be done by placing it in an oven at 60°C for 10 minutes. If necessary, the vacuuming and drying steps can be repeated up to 3 times.

[0017] Optionally, if a dense electret polymer film is required, polymer tape can be used instead. This eliminates the need for a hot-pressing step, and polymer tape can be directly applied to both sides of the composite microporous fiber and nanoparticle film.

[0018] According to one aspect of the present invention, a sandwich electret film of composite microporous fibers and nanoparticles prepared by the method of the present invention is provided.

[0019] According to one aspect of the invention, an electrostatic generator is provided, which contains a sandwich electret film of composite microporous fibers and nanoparticles according to the invention.

[0020] Optionally, according to the electrostatic generator of the present invention, the assembly method of the electrostatic generator includes the following steps: The electrostatic generator mainly consists of a cylindrical slider, a circular sandwich electret film (the area of ​​which is the same as the bottom area of ​​the cylindrical slider) made of composite microporous fibers and nanoparticles attached to the bottom of the cylindrical slider, and two parallel square electrode plates with a certain gap. The sandwich electret film is prepared by corona discharge, then cut into a circular shape, attached to the bottom of the cylindrical slider, and placed on the square electrode plates. Due to the principle of electrostatic induction, when the cylindrical slider slides back and forth between the two square electrode plates, a charge is generated in the external circuit connected by the two square electrodes, thus producing an electrical output in the external circuit.

[0021] The beneficial effects of this invention are as follows: (1) After the microporous fiber and nanoparticle film are mixed, the nanoparticles can be dispersed on the surface of the microporous fiber film. The composite sandwich film can be bonded together more tightly after hot pressing.

[0022] (2) The sandwich film of composite microporous fiber and nanoparticle has a smooth surface and higher surface potential and stability compared with single-layer electret film.

[0023] (3) The preparation process of sandwich films of composite microporous fibers and nanoparticles is simple and requires less equipment.

[0024] (4) In Application Example 1, the sandwich film of composite microporous fiber and nanoparticle according to the present invention was assembled into a sliding electrostatic generator after corona charging. Its open circuit voltage, short circuit current and working stability were tested. The test results showed that compared with the electrostatic generator of the same structure prepared by single-layer electret film of the same thickness, the electrostatic generator prepared by the sandwich film of composite microporous fiber and nanoparticle according to the present patent has higher output and better stability.

[0025] (5) In Application Example 2, a sandwich electret film (FEP / composite microporous polytetrafluoroethylene fiber and nanoparticle film / FEP) of composite microporous fibers and nanoparticles was fabricated, and its long-term surface potential stability was tested. The results showed that compared with single-layer FEP electret films and single-layer microporous fiber electret films of the same thickness, the sandwich electret film of composite microporous fibers and nanoparticles had a higher surface potential and better stability. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the sandwich electret film structure of composite microporous fibers and nanoparticles of the present invention; Figure 2This is a schematic diagram of the process for fabricating the sandwich film of composite microporous fibers and nanoparticles according to the present invention. Figure 3 The images show a cross-sectional SEM (scanning electron microscope) image of the sandwich film composed of composite microporous fibers and nanoparticles in the fabrication method of the present invention, a schematic diagram of the process platform for fabricating sandwich electret films composed of composite microporous fibers and nanoparticles by corona discharge, and a schematic diagram of the charge distribution on the surface and interface of the film after corona discharge. Figure 4 This is a schematic diagram of the electrostatic generator of the present invention. Detailed Implementation

[0027] The specific embodiments described are merely illustrative of the present invention and do not constitute a limitation on the content of the present invention. The present invention will be further described and illustrated below in conjunction with specific embodiments.

[0028] Example 1

[0029] This invention provides a micro / nano composite electret thin film for micro-energy harvesting and a method for fabricating the same. A schematic diagram of the thin film structure is shown below. Figure 1 As shown, the structure mainly comprises a first layer of dense electret polymer film, a second layer of composite microporous fibers and nanoparticles, and a third layer of dense electret polymer film. A flowchart of the film fabrication process can be found here. Figure 2 Furthermore, an electrostatic generator incorporating the sandwich electret thin film of the present invention was fabricated, and a schematic diagram of the structure is shown below. Figure 3 As shown. The main steps include the following: The first step is the raw material preparation step: prepare a dispersion of nano-polytetrafluoroethylene particles and a microporous polytetrafluoroethylene fiber film.

[0030] The second step is the preparation of the nano-polytetrafluoroethylene particle dispersion: the nano-polytetrafluoroethylene particles are uniformly dispersed in a deionized water solvent to form a dispersion, wherein the PTFE nanoparticles have a particle size of 200 nm to 400 nm. After ultrasonic stirring for 30 min, a uniform and stable nanoparticle dispersion with a mass percentage of 30% is finally prepared.

[0031] The third step involves fixing the microporous PTFE fiber film onto a glass plate and placing it in a fume hood. The prepared nano-PTFE dispersion is then poured into the solution chamber of a spray gun. The spray gun is held perpendicular to the film surface, approximately 4 cm away, and sprayed evenly from left to right and top to bottom onto the microporous PTFE fiber film surface. The film is then placed in a 60 °C oven and dried for 10 minutes. This spraying and drying process is repeated three times. At this point, the composite microporous PTFE fiber and nanoparticle film is complete.

[0032] The fourth step involves attaching 0.03 mm thick polytetrafluoroethylene tape to the front and back of the prepared composite film. This completes the preparation of the sandwich film of composite microporous polytetrafluoroethylene fiber and nanoparticles, with a thickness of 0.07 mm. Figure 3 (a) is a cross-sectional SEM image of the sandwich film of composite microporous polytetrafluoroethylene fiber and nanoparticles.

[0033] The fifth step involves electretting the thin film under conditions of room temperature and relative humidity (RH) of 40–55%, such as... Figure 3 As shown in (b), a sandwich film of composite microporous PTFE fibers and nanoparticles was fixed on the lower electrode plate of a corona discharge, with the needle tip 2.5 cm from the film surface. The discharge voltage was -15 kV, and the discharge was performed for 10 min using an intermittent DC voltage application method with a duty cycle of 0.5. The discharge area was the entire 2.5 cm × 2.5 cm square region of the film. Finally, a sandwich electret film of composite microporous PTFE fibers and nanoparticles was prepared. Three sandwich electret films of composite microporous PTFE fibers and nanoparticles with the same parameters were prepared according to this method. Figure 3 (c) shows the charge distribution on the film surface and at the inner layer interface after corona discharge. In addition, for comparison, a single-layer polytetrafluoroethylene electret film with a thickness of 0.07 mm was prepared using the same corona discharge parameters.

[0034] Step 6: Assembly of the electrostatic generator based on the sandwich electret film of composite microporous polytetrafluoroethylene fiber and nanoparticles, as shown in the schematic diagram below. Figure 4 As shown: The prepared sandwich electret film of composite microporous PTFE fibers and nanoparticles was cut into circles with a radius of 4.5 mm using a cutter, and attached to the bottom of a cylindrical slider with a radius of 4.5 mm. A custom-made FPCB (flexible printed circuit board) was used as two square electrode plates with a side length of 10 mm. The cylindrical slider with the circular sandwich electret film of composite microporous PTFE fibers and nanoparticles attached to its bottom was placed on top of the square electrode plates. Thus, the electrostatic generator based on the sandwich electret film of composite microporous PTFE fibers and nanoparticles was completed.

[0035] The surface potential of electret films can be measured using an electrostatic generator. Three sandwich electret film samples (2.5 cm × 2.5 cm in area) composed of composite microporous polytetrafluoroethylene fibers and nanoparticles, prepared using the above method, had surface potentials of -2.1 kV, -2.35 kV, and -2.49 kV, with an average surface potential of -2.31 kV. An electrostatic generator was fabricated using the film with a surface potential of -2.35 kV. The initial open-circuit voltage of the electrostatic generator was 33 V, and the short-circuit current was 0.34 μA. After 7 days, the open-circuit voltage retention rate of the electrostatic generator was 81%.

[0036] In contrast, under the same corona discharge parameters, the average surface potential of a single-layer PTFE electret film of the same thickness is -1.8 kV. Furthermore, the electrostatic generator based on the single-layer PTFE electret film outputs an open-circuit voltage of 22V, a short-circuit current of 0.2 μA, and maintains an open-circuit voltage retention rate of 60% after 7 days. It can be seen that the sandwich electret film of composite microporous PTFE fibers and nanoparticles prepared in this invention has a higher surface potential and exhibits higher electrical output and stability when applied to an electrostatic generator.

[0037] Example 2

[0038] The present invention provides a method for preparing a sandwich electret thin film composed of composite microporous fibers and nanoparticles, the structural schematic diagram of which is shown below. Figure 1 As shown, it mainly consists of a first layer of dense electret polymer film, a second layer of composite microporous fiber and nanoparticle film, and a third layer of dense electret polymer film. See the fabrication flowchart. Figure 2 and Figure 3 A highly stable electret thin film was prepared, comprising the following steps: The first step, raw material preparation: prepare a dispersion of nano-polytetrafluoroethylene particles and a microporous polytetrafluoroethylene fiber film. The second step is the preparation of the nano-polytetrafluoroethylene particle dispersion: the nano-polytetrafluoroethylene particles are uniformly dispersed in a deionized water solvent to form a dispersion, wherein the PTFE nanoparticles have a particle size of 200 nm to 400 nm. After ultrasonic stirring for 30 min, a uniform and stable nanoparticle dispersion with a mass percentage of 30% is finally prepared.

[0039] The third step involves fixing the microporous PTFE fiber film onto a glass plate and placing it in a fume hood. The prepared nano-PTFE dispersion is then poured into the solution chamber of a spray gun. The spray gun is held perpendicular to the film surface, approximately 4 cm away, and sprayed evenly from left to right and top to bottom onto the microporous PTFE fiber film surface. The film is then placed in a 60°C oven and dried for 10 minutes. This spraying and drying process is repeated three times. At this point, the composite microporous PTFE fiber and nanoparticle film is complete.

[0040] In the fourth step, the following layers of polytetrafluoroethylene (PTFE) film were stacked in the following order from top to bottom: FEP (fluorinated ethylene propylene copolymer), composite microporous fiber film, and nanoparticle PTFE film. The FEP film was sandwiched between two layers of polyimide film and placed on a heating stage at 280 °C. The mixture was then hot-pressed at 5 MPa for 30 min. The final product was a sandwich film of composite microporous PTFE fiber film and nanoparticles with a thickness of 0.06 mm.

[0041] The fifth step involves electretting the thin film under conditions of room temperature and relative humidity (RH) of 40–55%, such as... Figure 3 As shown in (b), the film was fixed on the lower electrode plate of the discharge, with the needle tip 2.5 cm from the film surface. The discharge voltage was -15 kV, and the discharge was performed for 10 min using an intermittent DC voltage application method with a duty cycle of 0.5. The discharge area was the entire 2.5 cm × 2.5 cm square region of the film. The final product was a sandwich (FEP / composite microporous PTFE fiber and nanoparticle film / FEP) electret film after corona discharge. Three samples with the same parameters were prepared according to the above method. For comparison, three single-layer FEP electret films and three single-layer microporous PTFE electret films with a thickness of 0.06 mm were prepared under the same corona discharge parameters.

[0042] The composite microporous PTFE fiber film and nanoparticle sandwich (FEP / composite microporous PTFE fiber and nanoparticle film / FEP) electret film prepared according to the above steps has an average surface potential of -1.45 kV and a surface potential retention rate of 50% after 30 days. In comparison, the average surface potential of the FEP electret film of the same thickness is -1.2 kV and the surface potential retention rate after 30 days is 41.7%, and the average surface potential of the microporous fiber PTFE electret film of the same thickness is -1.16 kV and the surface potential retention rate after 30 days is 41.3%. Therefore, the composite microporous fiber and nanoparticle sandwich (FEP / composite microporous PTFE fiber and nanoparticle film / FEP) electret film prepared by this invention has a higher surface potential and better stability.

[0043] In summary, the preparation method according to the present invention can produce electret thin films with high surface potential and good stability, which have good application prospects in micro electrostatic generators, such as micro electrostatic generators, and in self-driven sensing.

[0044] The embodiments described above are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A method for fabricating micro-nano composite electret thin films for micro-energy harvesting, characterized in that, The method includes the following steps: 1) The nanoparticle dispersion is uniformly dispersed in a deionized aqueous solvent and stirred magnetically or ultrasonically. If heating is required, it is placed in a water bath at 30℃~100℃ to finally prepare a uniform and stable nanoparticle dispersion with a mass percentage of 10%~40%. 2) Fabrication of composite microporous fiber and nanoparticle film: The prepared nanoparticle dispersion is loaded into the solution chamber of an airbrush. In a fume hood, a layer of nanoparticle dispersion is sprayed onto the surface of the microporous fiber film by spraying. The nanoparticles are sprayed into the interfiber gaps of the microporous fiber film by the air pressure of the airbrush. After spraying, the microporous fiber film is placed in a 60°C oven to dry. Then, the back side of the microporous fiber film is sprayed according to the above steps. The double-sided spraying and drying steps are repeated 3 to 5 times to finally obtain a composite microporous fiber and nanoparticle film. 3) Fabrication of sandwich film of composite microporous fiber and nanoparticle: First, the dense electret polymer film is ultrasonically cleaned and then dried in an oven at 60°C. Next, the three layers of film are stacked in the following order from top to bottom: dense electret polymer film, composite microporous fiber and nanoparticle film, and dense electret polymer film. The stacked three layers of film are sandwiched between two layers of polyimide film with high heat resistance. Then, the above five layers of film are placed on a heating table and a weight of appropriate weight is placed on it. The film is hot-pressed for 10~30 min to form sandwich film of composite microporous fiber and nanoparticle. 4) Fabrication of sandwich electret films using corona discharge method: A sandwich film of composite microporous fibers and nanoparticles is attached to the lower electrode plate of a corona discharge device. Under the condition of relative humidity RH of 40-55%, a voltage of -10kV to -18kV is applied to the tip of the needle. The intermittent DC voltage application method with a duty cycle of 0.1-1 is used. The distance between the tip of the needle and the lower electrode is 0.1-5 cm. The discharge is carried out for 1-10 minutes at room temperature, and finally a sandwich electret film of composite microporous fibers and nanoparticles, i.e., a micro-nano composite electret film, is obtained. The nanoparticles are made of one of the following materials: polytetrafluoroethylene, fluorinated ethylene propylene copolymer, polypropylene, perfluoroethylene propylene, polyvinylidene fluoride, and silicon dioxide, and the particle size of the nanoparticles is 0.01~500 nm. The microporous fiber membrane is made of one of the following materials: polytetrafluoroethylene, fluorinated ethylene propylene copolymer, polypropylene, perfluoroethylene propylene, polyvinylidene fluoride, polyvinyl butyral, polystyrene, polyester, polyvinyl acetate, nylon 6, nylon 66, polyvinyl alcohol, polymethyl methacrylate, polyaniline, polyethylene oxide, polyvinylpyrrolidone, polyacrylonitrile, polyethylene glycol, polyurethane, polysulfone, polyethersulfone, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-tetrafluoroethylene-perfluoromethyl vinyl ether, and polyvinylidene fluoride-trifluorochloroethylene. The micropore size of the microporous fiber membrane is 0.02~3 μm. The dense electret polymer film material is one of polytetrafluoroethylene, fluorinated ethylene propylene copolymer, polychlorotrifluoroethylene, ethylene tetrafluoroethylene copolymer, perfluoropolymer, polyvinylidene fluoride, polyvinylidene fluoride trifluoroethylene copolymer, polypropylene, polyimide, polyethylene terephthalate, polyethylene, and cycloolefin copolymer, and the thickness of the dense electret polymer film is 0.01~0.1 mm.

2. The method for fabricating micro / nano composite electret thin films for micro-energy harvesting according to claim 1, characterized in that: In the uniform dispersion step, the magnetic stirring or ultrasonic stirring operation involved is as follows: the dispersion is magnetically stirred at room temperature for 10-30 min, or ultrasonically vibrated for 10-30 min at a temperature of 30-50℃ and a power of 60-100 W.

3. The method for fabricating micro / nano composite electret thin films for micro-energy harvesting according to claim 2, characterized in that: The method of combining microporous fibers and nanoparticles uses vacuuming instead of spraying. The specific vacuuming method is as follows: the microporous fiber film is placed in the nanoparticle dispersion, then placed in a vacuum chamber, and vacuumed for 10-20 minutes. During this process, the air in the microporous fiber film is expelled, which will draw in the nanoparticles in the dispersion. Finally, the microporous fiber film is taken out and placed in an oven at 60°C for 10 minutes to dry. The vacuuming and drying steps are repeated 3 times.

4. The method for fabricating micro / nano composite electret thin films for micro-energy harvesting according to claim 3, characterized in that: When dense electret films are replaced with polymer tape, the hot pressing step can be eliminated, and polymer tape can be directly attached to both sides of the composite microporous fiber and nanoparticle film.

5. A sandwich electret film of composite microporous fibers and nanoparticles prepared by the method according to any one of claims 1-4, characterized in that, The film consists of, from top to bottom, a first layer of dense electret polymer film, a second layer of composite microporous fiber and nanoparticle film, and a third layer of dense electret polymer film.

6. An electrostatic generator comprising a sandwich electret thin film of composite microporous fibers and nanoparticles as described in claim 5, characterized in that, The electrostatic generator comprises a cylindrical slider, a circular sandwich electret film of composite microporous fibers and nanoparticles attached to the bottom of the cylindrical slider, and two parallel square electrode plates with a certain gap. The area of ​​the sandwich electret film is the same as the bottom area of ​​the cylindrical slider. The sandwich electret film of composite microporous fibers and nanoparticles is cut into a circular shape, attached to the bottom of the cylindrical slider, and placed on the square electrode plates. Due to the principle of electrostatic induction, when the cylindrical slider slides back and forth between the two square electrode plates, charges will move back and forth in the external circuit connected to the two square electrode plates, thereby generating an electrical output in the external circuit.

Images