Preparation method and application of circumferentially limited supercritical foaming self-packaging TENG

Abstract

The invention discloses a preparation method and application of circumferentially limited supercritical foaming self-packaging TENG, and the preparation method comprises the following steps: uniformly mixing a PDMS precursor and a curing agent, pouring the mixture into a mold, and putting the mold into a vacuum oven for curing to obtain a PDMS film; adhering the PDMS film to the middle position of the PI film through a double-sided nickel conductive adhesive tape, then putting the PDMS film into a mold, putting a thermoplastic elastomer on the upper layer, and performing hot pressing by using a vacuum auxiliary hot press to obtain a prefabricated sample; putting the prefabricated sample into a supercritical foaming reaction kettle, controlling the temperature to 70-130 DEG C, injecting supercritical fluid into the foaming reaction kettle, after the prefabricated sample and the supercritical fluid form a saturated and stable blending system, maintaining for 0.8-1.5 hours, taking out the blended system, and naturally cooling to room temperature, so as to obtain the TENG. The preparation method has the beneficial effects that the self-assembled and self-packaged TENG with the bionic dome structure is successfully prepared through cooperation of a supercritical fluid technology and a limited foaming strategy, and the technical scheme of the self-assembled and self-packaged TENG obtains breakthrough progress in the aspects of the preparation process, the structural design and the environmental adaptability.

Description

Technical Field

[0001] The present invention relates to the technical field of triboelectric nanogenerators, and particularly relates to a preparation method and application of a circumferentially restricted supercritical foaming self-encapsulated TENG. Background Art

[0002] As a highly promising new energy technology, the triboelectric nanogenerator (TENG) shows great application potential in the fields of self-powered sensing, wearable devices, and environmental monitoring. However, its practical application is still limited by key issues such as structural design and environmental adaptability. Traditional TENGs rely on independent support units (such as springs, foams, etc.) to maintain a fixed friction space, and then manual assembly is carried out, resulting in complex preparation processes, long processing cycles, and poor sample molding consistency. At the same time, its output performance is greatly affected by environmental humidity. Usually, methods such as modifying the material surface to be hydrophobic and post-treatment encapsulation are adopted. However, in the scheme of modifying the surface to be hydrophobic, the friction material surface is still directly exposed to the environment, so its protection performance is limited. And for the post-treatment encapsulation scheme, there are problems such as complex preparation processes and difficulty in continuous large-scale production.

[0003] For example, a triboelectric nanogenerator and test device disclosed in Patent CN211018678U is applied between the track and the bed plate of the railway system and installed at the midpoint of the rail section between every two adjacent sleepers. The triboelectric nanogenerator includes a layered structure and an insulating and waterproof encapsulation protection layer covering the layered structure. The layered structure includes an upper support layer, an upper electrode layer, a friction pair, a lower electrode layer, a lower support layer, and a buffer layer from top to bottom; CN110277936A discloses a triboelectric nanogenerator. An elastic material is designed as the electrode substrate of the triboelectric nanogenerator. On this basis, carbon nanotubes are added as a conductive material, and polydopamine and borax are introduced into the flexible electrode to make it have a self-healing function when encountering water. Finally, it is encapsulated with highly flexible silica gel to realize the flexible application and repairable application of the triboelectric nanogenerator. The present invention not only designs a triboelectric nanogenerator with good flexibility and high biosecurity, which can collect the tiny frictional movement energy generated during human movement and apply it to wearable electronic devices, but also introduces a repairable function into traditional flexible materials, overcoming the defects of wearable materials being easily worn and broken. The above methods all require an insulating and waterproof encapsulation process, and there are problems such as complex preparation processes, poor sample molding consistency, high time-consuming cost, and inability to produce continuously.

[0004] In addition, patent document CN111953226A discloses an implantable triboelectric nanogenerator and its preparation method and application. To design and prepare a triboelectric nanogenerator with a simple preparation method, an implantable triboelectric nanogenerator is provided, which includes a packaging layer, a friction layer, and a conductive hydrogel. The friction layer and the pits of the packaging layer form a closed void. The void of this triboelectric nanogenerator is carbon dioxide, which can be generated spontaneously in the void without additional inflation, simplifying the preparation method and improving production efficiency. However, in this preparation method, the outer layer material can only use thermosetting materials such as silicone rubber elastomers like Ecoflex, which is not foamed and cannot be foamed, so the elasticity cannot be further improved. Moreover, its positive friction layer uses PVA hydrogel, which contains a large amount of water and inorganic salts (such as lithium chloride, sodium bicarbonate, etc.), has a corrosive effect on metal electrodes, and the sealed space after encapsulation is still in a humid environment. At the same time, the gas cavity (friction space) in the encapsulation and assembly process completely relies on the decomposition of sodium bicarbonate, with limited gas loading and a single type (only CO2 can be generated), and the release process is not easy to control, having great limitations. Summary of the Invention

[0005] Aiming at the key problems of the current TENG, such as complex assembly process and being affected by the environment (especially humidity), the present invention provides a preparation method and application of a circumferentially restricted supercritical foaming self-encapsulated TENG, aiming to utilize the green and efficient supercritical fluid foaming technology to achieve the controllable construction of a bionic dome structure self-assembled and self-encapsulated elastomer foam-based TENG through locally restricted foaming, as shown in Figure 1 to significantly improve the mechanical entropy energy harvesting effect of the elastomer foam-based TENG and assist in the large-scale continuous industrial production and commercial application of the elastomer foam-based TENG and its related self-powered sensing devices.

[0006] To achieve the above invention purpose, a preparation method of a circumferentially restricted supercritical foaming self-encapsulated TENG provided by the present invention specifically includes the following steps: The first step: Prepare a preform Mix the PDMS precursor and the curing agent evenly, pour them into a mold and cure them in a vacuum oven to obtain a PDMS film; wherein, the mass ratio of the PDMS precursor to the curing agent is 8-12:1, preferably 10:1; Attach the PDMS film to the center position of the PI film through a double-sided nickel conductive tape, then put it into a mold, and place a thermoplastic elastomer on the upper layer, and use a vacuum-assisted hot press to hot press to obtain a preform; the double-sided nickel conductive tape is externally connected to a stainless steel wire; wherein, the thermoplastic elastomer is a positively charged thermoplastic elastomer, specifically any one of TPU, PEbax, TPEE, and SEBS.

[0007] Step 2: Supercritical fluid foaming Place the prefabricated sample into a supercritical foaming reactor, control the foaming temperature to 70 - 130 °C, inject the supercritical fluid into the foaming reactor under pressure. After the prefabricated sample and the supercritical fluid form a saturated and stable blend system within the pressure range of 5 - 20 MPa, maintain for 0.8 - 1.5 h, then take out and naturally cool to room temperature to obtain the TENG; the supercritical fluid is scCO2 or scN2. Preferably, the foaming temperature is 100 - 120 °C, and the effect is best at 110 °C; the saturated pressure is preferably 10 - 20 MPa, and the output performance is best at 15 MPa.

[0008] The distance between the edge of the PDMS film and the edge of the PI film, or the contact width between the PDMS film and the thermoplastic elastomer is 7 - 15 mm, preferably 10 mm.

[0009] The curing temperature of the vacuum oven is 100 - 120 °C, and the curing time is 0.8 - 1.5 h; preferably, the curing temperature is 110 °C and the curing time is 1 h.

[0010] The hot pressing temperature of the vacuum-assisted hot press is 150 - 200 °C, and the hot pressing time is 8 - 12 min; preferably, the hot pressing temperature is 180 °C and the hot pressing time is 10 min. The self-encapsulated TENG of the present invention includes a PI film, a thermoplastic elastomer foaming film, and a PDMS film adhered to the middle position of the inner surface of the PI film by a double-sided nickel conductive tape; The edge of the thermoplastic elastomer foaming film is hermetically connected to the edge of the PI film, and its middle part forms a dome structure with the PI film to form a friction space, and the friction space is filled with dry foaming gas overflowing during the foaming of the thermoplastic elastomer; The PDMS film is a positive friction layer; The thermoplastic elastomer foaming film is a negative friction layer and also a packaging layer; The double-sided nickel conductive tape is externally connected with a stainless steel wire; Among them, the thermoplastic elastomer is a positively charged thermoplastic elastomer, specifically any one of TPU, PEbax, TPEE, and SEBS.

[0011] In order to better achieve the above-mentioned invention purpose, the circumferentially restricted supercritical foaming self-encapsulated TENG can be applied in a fluid control system. Specifically, the self-encapsulated TENG is used as a self-powered mechanical sensor, generates an electrical signal by detecting the fluid impact force or mechanical deformation, and transmits the electrical signal to a terminal device through a wireless transmission module to realize on-line monitoring and remote flow control of the water flow parameters at the water outlet.

[0012] The beneficial effects of the present invention are as follows: Through an environmentally friendly, simple, and efficient method, the present invention prepares a TENG with self-assembly and self-encapsulation characteristics of a bionic dome structure. Through the synergy of supercritical fluid technology and circumferentially constrained foaming strategy, a self-assembled and self-encapsulated TENG with a bionic dome structure is successfully prepared. Its technical solution has made breakthrough progress in the preparation process, structural design, and environmental adaptability, specifically reflected in the following advantages: (1) One-step green preparation process: By regulating the saturation pressure and foaming temperature, the in-situ self-assembly of the bionic dome structure in the friction space and the simultaneous self-encapsulation of the device are achieved. Compared with the traditional TENG process, the steps of assembling the support unit and secondary encapsulation are omitted, the processing cycle is shortened by more than 40%, and there is no solvent residue; (2) Fully enclosed anti-interference structure: The airtight friction space filled with foaming gas isolates environmental humidity. Combined with the strong interfacial bonding force between the outer encapsulation of the thermoplastic elastomer foaming film and the PDMS negative friction layer, the TENG can achieve stable underwater output and be used as a self-powered sensor in high-humidity environments; (3) Synergistic design of multifunctional materials: The thermoplastic elastomer foaming film has dual functions of a positive friction layer and an encapsulation layer, and has a protective effect on metal electrodes (nickel and stainless steel wires); (4) Breakthrough in strengthening mechanical properties: The bionic dome structure formed by circumferentially constrained supercritical foaming endows the device with super elasticity, effectively solving the problem of friction gap failure caused by mechanical fatigue in traditional TENGs. Description of the Drawings

[0013] Figure 1 Schematic diagram of the morphological bionic jellyfish of the self-encapsulated TENG in Examples 1-5.

[0014] Figure 2 Schematic diagram of the one-step forming principle of the self-encapsulated TENG in Examples 1-5.

[0015] Figure 3 Comparison diagram before and after the preform foaming and forming of the self-encapsulated TENG method in Example 2.

[0016] Figure 4 Schematic diagram of the macroscopic morphology regulation of the self-encapsulated TENG in Example 6.

[0017] Figure 5 Schematic diagram of the compression deformation process, triboelectric generation principle, and potential simulation results during the deformation process of the self-encapsulated TENG in Example 7.

[0018] Figure 6 Schematic diagram of the pressure resistance (run over by a car) and underwater performance test of the self-encapsulated TENG in Example 7.

[0019] Figure 7Schematic diagram of the self-encapsulated TENG in Example 7 as a self-powered sensor for its response to different forces and for wireless sensing for controlling and monitoring the water flow at the water outlet. Detailed implementation mode

[0020] The present invention realizes a one-step method for a self-encapsulated TENG with a bionic dome structure (such as Figure 1 ) through locally confined foaming. As shown in Figure 2 , a thermoplastic elastomer (such as TPU, etc.), PDMS, a conductive nickel tape, and a polyimide film (PI film) are tightly hot-pressed together through vacuum hot-pressing treatment to obtain a composite material preform, wherein the thermoplastic elastomer and the polyimide film (PI film) completely wrap PDMS and the conductive nickel tape. During the foaming process of the preform, due to the extremely strong interfacial bonding force between the thermoplastic elastomer and PI, the growth of nucleation sites is restricted after supercritical soaking treatment. Along with the processes of gas nucleation, growth, and overflow, the firm interfacial bonding between the thermoplastic elastomer and PI is restricted, and a large amount of gas overflows, resulting in a very low foaming ratio or even no foaming at this place. On the contrary, due to the extremely low interfacial bonding between the thermoplastic elastomer and PDMS, during the foaming and expansion process of TPU, it separates from the PDMS layer and expands outward to form a sealed air chamber, and at the same time, the overflowing foaming gas (mainly from PDMS and TPU) fills the air chamber, synchronously completing the self-assembly and self-encapsulation molding of the TENG.

[0021] To clearly illustrate the technical features of this solution, the following elaborates on this solution through specific implementation modes.

[0022] Example 1 The embodiment of the present invention provides a preparation method for a circumferentially confined supercritical foaming self-encapsulated TENG, including the following steps: The first step: Prepare the preform Mix the PDMS precursor and the curing agent evenly according to a mass ratio of 10:1, pour it into a mold, and cure it in a vacuum oven at 110 °C for 1 h to obtain a PDMS film; Attach the PDMS film to the central position of the PI film through a double-sided nickel conductive tape, then put it into a mold, and place TPU pellets on the upper layer. The contact width between the PDMS film and the TPU pellets is 10 mm, and use a vacuum-assisted hot press to hot-press at 180 °C for 10 min to obtain a preform; wherein, a stainless steel wire is externally connected to the double-sided nickel conductive tape; The second step: Supercritical fluid foaming Put the preform into a supercritical foaming reactor, control the temperature to 110 °C, inject scCO2 under pressure into the foaming reactor. After the preform and scCO2 form a saturated and stable blend system, maintain it for 1 h, take it out and naturally cool it to room temperature to obtain the TENG.

[0023] Example 2 An embodiment of the present invention provides a preparation method of a circumferentially restricted supercritical foaming self - encapsulated TENG, including the following steps: The first step: preparing a preform Mix the PDMS precursor and the curing agent evenly according to a mass ratio of 10:1, pour them into a mold with dimensions of 40 mm×40 mm×0.1 mm, and place them in a vacuum oven for curing at 110 °C for 1 h to obtain a PDMS film; Use a double - sided nickel conductive tape of the same area to stick the PDMS film at the central position of a PI film with dimensions of 50 mm×50 mm×0.25 mm, then place it in a mold with dimensions of 50 mm×50 mm×0.95 mm, and put TPU pellets on the upper layer. Use a vacuum - assisted hot press to hot - press at 180 °C for 10 min to obtain a preform; wherein, the double - sided nickel conductive tape is externally connected with a stainless - steel wire; The second step: supercritical fluid foaming Put the preform into a supercritical foaming reactor, use a temperature control system to precisely control the internal temperature of the reactor to reach the preset foaming temperature of 110 °C, inject scCO2 into the foaming reactor through a gas supply system. After the preform and scCO2 form a saturated and stable blend system at a pressure of 15 MPa, maintain for 1 h, take it out and naturally cool to room temperature to obtain a TENG. Figure 3 Shows the comparison before and after the preform foams. The TPU layer is filled with dense bubbles, changes from transparent to white, and the TPU bulges after being restricted by the PI film during the foaming process, forming a dome structure.

[0024] Example 3 An embodiment of the present invention provides a preparation method of a circumferentially restricted supercritical foaming self - encapsulated TENG, including the following steps: The first step: preparing a preform Mix the PDMS precursor and the curing agent evenly according to a mass ratio of 8:1, pour them into a mold, and place them in a vacuum oven for curing at 100 °C for 1.5 h to obtain a PDMS film; Stick the PDMS film to the centered position of the PI film through a double - sided nickel conductive tape, then place it in a mold, and put TPU pellets on the upper layer. The contact width between the PDMS film and the TPU pellets is 8 mm. Use a vacuum - assisted hot press to hot - press at 150 °C for 12 min to obtain a preform; wherein, the double - sided nickel conductive tape is externally connected with a stainless - steel wire; The second step: supercritical fluid foaming Put the preform into a supercritical foaming reactor, control the temperature to 100 °C, inject scN2 under pressure into the foaming reactor. After the preform and scN2 form a saturated and stable blend system at a pressure of 20 MPa, maintain for 1.5 h, take it out and naturally cool to room temperature to obtain a TENG.

[0025] Example 4 The embodiment of the present invention provides a method for preparing a circumferentially restricted supercritical foaming self-encapsulated TENG, comprising the following steps: Step 1: Prepare the preform The PDMS precursor and curing agent were mixed evenly in a mass ratio of 12:1, poured into a mold, and placed in a vacuum oven for curing at 120°C for 0.8h to obtain a PDMS film; The PDMS film was adhered to the center of the PI film through a double-sided nickel conductive tape, and then placed in a mold, and TPU pellets were placed on the upper layer. The contact width between the PDMS film and the TPU pellets was 15 mm. A vacuum-assisted hot press was used for hot pressing at 200°C for 8 minutes to obtain a prefabricated sample; wherein the double-sided nickel conductive tape was externally connected to a stainless steel wire; Step 2: Supercritical Fluid Foaming The prefabricated sample was placed in a supercritical foaming reactor, the temperature was controlled to 130°C, and scCO2 was pressurized and injected into the foaming reactor. After the prefabricated sample and scCO2 formed a saturated and stable blending system under a pressure of 10 MPa, it was maintained for 0.8 h, taken out and naturally cooled to room temperature to obtain TENG.

[0026] Example 5 This embodiment provides a self-encapsulated TENG, comprising a PI film, a thermoplastic elastomer foam film, and a PDMS film adhered to the center of the inner surface of the PI film by a double-sided nickel conductive tape; The edge of the thermoplastic elastomer foam film is sealed and connected to the edge of the PI film, and the middle part thereof is in a dome structure to form a friction space with the PI film. The friction space contains dry foaming gas overflowed during the foaming of the thermoplastic elastomer. The PDMS film is a positive friction layer; The thermoplastic elastomer foam film is a negative friction layer and also an encapsulation layer; The double-sided nickel conductive tape is connected to a stainless steel wire; The thermoplastic elastomer may be any one of the positively charged thermoplastic elastomers TPU, PEbax, TPEE, and SEBS; and the TPU in Examples 1-4 may be replaced by any one of the positively charged thermoplastic elastomers.

[0027] Example 6 In any of the preparation methods of Examples 1-4 of the present invention, the macroscopic structure of the TENG prepared by locally confining the thermoplastic elastomer can be precisely controlled by adjusting the foaming parameters (such as foaming temperature, saturation pressure, etc.). Figure 4 As shown in the example, Figure 4shows the voltage of the self-assembled and self-encapsulated TENG prepared at the same pressure (15 Mpa) and different temperatures (70 - 130 °C) ( Figure 4 a) and current ( Figure 4 b), as well as the influence of macroscopic morphology ( Figure 4 c). By adjusting the foaming temperature, precise control of the performance and macroscopic morphology of the self-encapsulated TENG is achieved. It can be seen that the output performance of the TENG obtained by supercritical foaming at 70 - 130 °C can meet the requirements, and the TENG foamed at 110 °C has the best output performance.

[0028] Example 7 For the circumferentially confined supercritical foaming self-encapsulated TENG prepared in Example 1 of the present invention, its positive and negative friction layers (TPU and PDMS) are in a completely enclosed environment, and the enclosed environment is completely filled with dry foaming gas, which has a protective effect on the metal electrodes (nickel and stainless steel wires), overcoming the shortcomings of traditional TENGs restricted by the environment, especially the influence of humidity. Therefore, the self-encapsulated TENG of the present invention can achieve stable underwater output and be used as a self-powered sensor in a high-humidity environment. As Figure 6 shown, Figure 6 the left figure in shows the compressive test of the self-encapsulated TENG (green) and the non-self-encapsulated TENG (orange) by using a car to roll over. After the self-encapsulated TENG is subjected to high-intensity extrusion, its morphology is significantly better maintained than that of the post-encapsulated TENG, and a performance test is carried out. In contrast, the current output of the self-encapsulated TENG does not decay before and after being compressed; in addition, as Figure 6 the right figure in shows the humidity resistance performance of the self-encapsulated TENG. The self-encapsulated TENG is repeatedly pinched by hand and the output current signal is detected. When directly transitioning from air (green) to underwater (orange), the output signal does not change. As Figure 7 shown, through Figure 7 the performance test experiments of one finger and two fingers in a, and Figure 7 slow stepping and fast stepping with the foot in b, it shows the sensitivity of the self-encapsulated TENG, which can quickly respond to forces of different magnitudes and frequencies. For this purpose, the circuit connection diagrams and actual connected photos shown in Figure 7 c and Figure 7 d are designed. Figure 7 e is Figure 7 the mobile phone app display interface when the c system is running. While controlling the water output through the self-assembled TENG, the size and duration of the water flow can be monitored in real time through the interface. Figure 7 f shows that when the self-assembled TENG is stepped on by foot four times, the voltage (after filtering) each time is basically the same, proving its stability of the output signal during operation.

[0029] Compared with traditional TENGs, the self-encapsulated TENG prepared in the present invention does not require an independent support unit (such as a spring, foam, etc.) to maintain a fixed friction space, nor does it require additional secondary manual assembly and encapsulation processes. The foamed TPU and the foaming gas in the friction space surrounded by PI play a very good supporting role for the entire TENG device, ensuring that it can still rebound and recover its original shape after being deformed under pressure. As Figure 5 shown, it records the release process of the self-encapsulated TENG after being compressed, as well as the working mechanism of the continuous electrical energy generation caused by repeated flattening and release (i.e., the contact separation of the positive and negative friction layers) and the finite element potential simulation diagram.

[0030] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A preparation method of a circumferentially restricted supercritical foaming self-encapsulated TENG, characterized in that, The preparation method includes the following steps: The first step: preparing a preform Mix the PDMS precursor and the curing agent evenly, pour the mixture into a mold and place it in a vacuum oven for curing to obtain a PDMS film; Attach the PDMS film to the center position of the PI film through a double-sided nickel conductive tape, then place it in a mold, and put a thermoplastic elastomer on the upper layer, and use a vacuum-assisted hot press for hot pressing to obtain a preform; The second step: supercritical fluid foaming Place the preform in a supercritical foaming reactor, control the temperature to 70-130 °C, inject the supercritical fluid into the foaming reactor under pressure. After the preform and the supercritical fluid form a saturated and stable blend system, maintain for 0.8-1.5 h, take it out and cool it naturally to room temperature to obtain a TENG.

2. The preparation method according to claim 1, characterized in that, The mass ratio of the PDMS precursor to the curing agent is 8-12:

1.

3. The preparation method according to claim 1, characterized in that, The distance between the edge of the PDMS film and the edge of the PI film, or the contact width between the PDMS film and the thermoplastic elastomer is 7-15 mm.

4. The preparation method according to claim 1, characterized in that, The curing temperature of the vacuum oven is 100-120 °C, and the curing time is 0.8-1.5 h.

5. The preparation method according to claim 1, wherein The double-sided nickel conductive tape is externally connected with a stainless steel wire.

6. The preparation method according to claim 1, wherein The hot pressing temperature of the vacuum-assisted hot press is 150-200 °C, and the hot pressing time is 8-12 min.

7. The preparation method according to claim 1, characterized in that, In the second step, the thermoplastic elastomer is a positively charged thermoplastic elastomer, specifically any one of TPU, PEbax, TPEE and SEBS.

8. The preparation method according to claim 1, wherein, The supercritical fluid is scCO2 or scN2.

9. A self-encapsulated TENG, characterized in that, It includes a PI film, a thermoplastic elastomer foamed film, and a PDMS film adhered to the center position of the inner surface of the PI film by a double-sided nickel conductive tape; The edge of the thermoplastic elastomer foamed film is hermetically connected to the edge of the PI film, and its middle part forms a dome structure to form a friction space with the PI film, and the friction space is filled with dry foaming gas overflowed during the foaming of the thermoplastic elastomer; The PDMS film is a positive friction layer; The thermoplastic elastomer foamed film is a negative friction layer and also a packaging layer; The double-sided nickel conductive tape is externally connected with a stainless steel wire; Among them, the thermoplastic elastomer is a positively charged thermoplastic elastomer, specifically any one of TPU, PEbax, TPEE and SEBS.

10. The application of the self-encapsulated TENG obtained by the preparation method according to any one of claims 1-8, or the self-encapsulated TENG according to claim 9, in a fluid control system, characterized in that, The self-encapsulated TENG, as a self-powered mechanical sensor, generates electrical signals by detecting fluid impact force or mechanical deformation in real time, and transmits the electrical signals to a terminal device through a wireless transmission module to realize on-line monitoring of water outlet flow parameters and remote flow control.

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