Polyimide / silver composite nanofiber conductive aerogel with piezoresistive sensing performance and preparation method thereof

Abstract

The invention relates to polyimide / silver composite nanofiber conductive aerogel with piezoresistive sensing performance and a preparation method of the polyimide / silver composite nanofiber conductive aerogel. The method comprises the following steps: firstly, forming a silver seed layer on the surface of polyamide acid nanofiber through in-situ metallization; then, the polyimide / silver composite nanofiber aerogel and hot-melt polyamide acid nanofibers are dispersed in a specific solvent through high-speed stirring to prepare mixed dispersion liquid, and then the polyimide / silver composite nanofiber aerogel with a three-dimensional cross-linked network structure is obtained through freeze drying and thermal imidization; and finally, carrying out chemical plating on the aerogel again to enable the silver particles on the surface of the fiber to further grow into a compact silver layer, thereby obtaining the polyimide / silver composite nanofiber conductive aerogel with the piezoresistive sensing performance. The aerogel prepared by the method has good flexibility, rebound resilience and excellent conductivity and piezoresistance, the preparation process is simple and controllable, industrial preparation is easy, and the aerogel has wide application prospects in the field of flexible sensing.

Description

Technical Field

[0001] The invention belongs to the field of polymer nanomaterials and strain sensing, and in particular relates to a polyimide / silver composite nanofiber conductive aerogel with piezoresistive sensing performance and a preparation method thereof. Background Art

[0002] Piezoresistive sensors use applied pressure to cause changes in the resistivity of materials, thereby achieving accurate monitoring of external pressure or strain. This technology is widely used in health monitoring, electronic skin, smart textiles, robot tactile perception and other fields, especially in situations where highly sensitive and reliable responses are required. However, with the expansion of application areas, the performance requirements for piezoresistive sensors are also increasing, especially in terms of sensitivity, stability, flexibility and scalability. The performance of piezoresistive sensors depends to a large extent on the electrical and mechanical properties of the sensing material. Traditional piezoresistive materials are mostly hard metals or semiconductor materials. Although these materials have high sensitivity in some occasions, their rigidity and fragility limit their application in flexible electronic devices.

[0003] Aerogel materials have become important candidate materials in the field of piezoresistive sensors due to their extremely high specific surface area, low density, good thermal stability and excellent flexibility. In particular, when conductive fillers (such as carbon nanotubes, graphene, nanometals, etc.) are introduced into the aerogel matrix, the material not only maintains good flexibility, but also significantly improves its conductivity and piezoresistive effect. However, these materials still have limitations in application, such as the conductive fillers are easy to aggregate, resulting in uneven dispersion, and the poor adhesion of nanometals to the matrix material, which is also an important factor limiting their widespread application.

[0004] Therefore, there is an urgent need to develop a technology that can evenly disperse conductive fillers in the polymer aerogel matrix and enhance its adhesion, which can not only enhance the piezoresistive effect of the composite aerogel, but also improve its long-term stability and reusability, providing new ideas for the preparation of composite conductive aerogels that can be used in the field of flexible piezoresistive sensing. Summary of the invention

[0005] The present invention aims to solve the technical problems of poor compression recovery, poor cyclic stability and poor micro-strain detection capability of current composite conductive aerogel materials, and provides a polyimide / silver composite nanofiber aerogel with excellent resilience, good conductivity and stable response and a preparation method thereof. The composite aerogel prepared by the present invention has excellent fatigue resistance and cyclic stability, and has good application prospects in the field of flexible sensing.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a polyimide / silver composite nanofiber aerogel. The framework of the composite aerogel is polyimide nanofibers, and the fibers penetrate and interlace with each other to form a three-dimensional nano-network structure. A silver layer is coated on the surface of the fibers to form a three-dimensional conductive network structure.

[0008] Furthermore, the diameter of the polyimide nanofibers is 20 - 1000 nm, preferably 100 - 500 nm.

[0009] Furthermore, the volume density of the polyimide / silver composite conductive nanofiber aerogel is 20 - 200 mg / cm 3 。

[0010] A preparation method of a conductive polyimide / silver nanofiber composite aerogel with piezoresistive sensing performance comprises the following steps:

[0011] A: A polyamic acid solution is obtained by polycondensation reaction of diamine monomers and dianhydride monomers, and then polyamic acid nanofibers are obtained through electrospinning and further drying treatment. According to the types of dianhydride and diamine monomers, thermosetting and hot-melt polyamic acid nanofibers can be respectively prepared;

[0012] B: The thermosetting polyamic acid nanofibers prepared in step A are placed in an aqueous silver salt solution for ion exchange, and then placed in an aqueous reducing agent solution for reduction to form a silver seed layer on the surface of the polyamic acid nanofibers;

[0013] C: The polyamic acid / silver composite nanofibers prepared in step B and the hot-melt nanofibers prepared in step A are dispersed in a specific solvent through high-speed stirring to obtain a nanofiber mixed dispersion liquid, and then through freeze-drying and thermal imidization treatment, a polyimide / silver composite nanofiber aerogel with silverization on the first surface is obtained;

[0014] D: An appropriate amount of silver salt and soluble base are dissolved in deionized water, and stirred to obtain a clear and transparent mixed solution 1, which is placed in the dark for standby; an appropriate amount of alcohol additive and weak reducing agent are dissolved in deionized water, and stirred to obtain a clear and transparent mixed solution 2, which is placed in the dark for standby; the solution 1 and 2 are mixed and stirred evenly to obtain an electroless plating solution, which is placed in the dark for standby.

[0015] E: The polyimide / silver composite nanofiber aerogel prepared in step C is placed in the electroless plating solution prepared in step D, taken out after impregnation for a period of time, washed and dried, and then a polyimide / silver composite nanofiber conductive aerogel with piezoresistive sensing performance is obtained.

[0016] Further, the solid content of the polyamic acid solution in step A is 5-40 wt%; the drying treatment is drying at 150°C for 0.5-3 h; the dianhydride used for preparing the thermosetting polyimide nanofibers is one or a mixture of two or more of biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), benzophenone tetracarboxylic dianhydride (BTDA), and the diamine is one or a mixture of two or more of diaminodiphenyl ether (ODA), p-phenylenediamine (PDA), 4,4'-diaminodiphenylmethane (MDA). The dianhydride used for preparing the hot-melt polyimide nanofibers is one or a mixture of two or more of hexafluorodiacid dianhydride (6FDA), 4,4'-diphenylethertetracarboxylic dianhydride (ODPA), bisphenol A dianhydride (BPADA), and the diamine is one or two of 4,4'-diaminodiphenyl ether (4,4'-ODA), m-phenylenediamine (MPD); the solvent used is one or more of N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide.

[0017] Further, the silver salt in step B is selected from one or more of silver chloride, silver cyanide, silver nitrate, silver acetate, silver fluoroborate, and silver trifluoromethanesulfonate, the solvent is deionized water, the solution concentration is 0.01-0.5 mol / L, the ion exchange time is 5-40 min, and the exchange temperature is 10-50°C; the reducing agent is selected from one or more of formaldehyde, glucose, dimethylaminoborane, ascorbic acid, and sodium hypophosphite, the solvent is deionized water, the solution concentration is 1-20 mmol / L, the reduction time is 1-10 min, and the reduction temperature is 10-50°C.

[0018] Further, the solid content of the nanofibers in step C is 0.5%-3%, and the ratio of the thermosetting composite nanofibers to the hot-melt nanofibers is 6:1-12:1; the solvent is an aqueous solution of tert-butanol, where the mass ratio of tert-butanol to water is 1:1-3:1.

[0019] Further, the high-temperature thermal imidization treatment process in step C is as follows: under a nitrogen atmosphere, it is heated from room temperature to 135°C in 1 h and held for 0.5 h, and then heated to 300°C in 1.5 h and held for 0.5 h.

[0020] Further, the silver salt in the electroless plating solution in step D is selected from one or more of silver chloride, silver cyanide, silver nitrate, silver acetate, silver fluoroborate, and silver trifluoromethanesulfonate; the soluble base is selected from one or more of ammonia water, potassium hydroxide, and sodium hydroxide; the alcohol auxiliary is selected from one or more of methanol, ethanol, n-propanol, and tert-butanol; the weak reducing agent is selected from one or more of glucose, glyoxal, formaldehyde, and potassium sodium tartrate.

[0021] Further, the immersion time of the polyimide / silver composite nanofiber aerogel described in step E in the electroless plating solution is 5 - 60 min, preferably 10 - 40 min.

[0022] Compared with existing materials and technologies, the present invention has the following beneficial effects:

[0023] (1) The polyimide nanofibers selected by the method of the present invention contain nanofibers that can be melted by heat. After high-temperature thermal imidization, they can act as cross-linking agents in the fibers to form effective adhesion; in addition, the silver nanoparticles diffuse and migrate during high-temperature thermal imidization, and then sinter on the fiber surface to form a dense silver layer, thereby endowing electrical conductivity and providing certain mechanical support for the nanofibers, enhancing the skeleton structure of the aerogel, and enabling the aerogel to exhibit good compression and rebound performance.

[0024] (2) In the method of the present invention, a silver seed layer is first generated on the fiber surface by in-situ metallization. Metal ions migrate from the shallow surface layer of the polymer matrix outward and are reduced to form a metal layer, thereby effectively solving the interfacial adhesion problem between the metal layer and the polymer matrix, achieving heterogeneous interface matching and excellent interfacial adhesion performance. Then, the seed layer is further grown and thickened by electroless plating to form a continuous conductive silver layer, thereby realizing efficient and controllable loading of a highly adhesive metal layer; this "one-time silver seeding and secondary growth" process is beneficial to the formation of a uniform and highly adhesive silver layer on the fiber surface, thereby forming a firm three-dimensional conductive network with the aerogel as the matrix, endowing the polyimide / silver composite nanofiber aerogel with excellent electrical conductivity and stable cyclic response performance.

[0025] (3) The preparation process of the method of the present invention is simple and controllable. The aerogel has a strong designability in terms of volume density, microporous structure, silver loading, and size and shape, is easy to mass-produce industrially, and has broad application prospects. Description of the Drawings

[0026] Figure 1 is a physical appearance diagram of the polyimide / silver composite nanofiber aerogel in Example 1;

[0027] Figure 2 is the SEM micrograph of the polyimide / silver composite nanofiber aerogel in Comparative Example 1 and Example 1;

[0028] Figure 3 is a curve diagram showing the change rate of resistance of the polyimide / silver composite nanofiber aerogel in Example 1 with the change of strain;

[0029] Figure 4 is a curve diagram showing the change rate of resistance of the polyimide / silver composite nanofiber aerogel in Example 1 under different strains;

[0030] Figure 5It is a graph showing the change rate of resistance of the polyimide / silver composite nanofiber aerogel in Example 1 with the number of cycles at 15% strain (3000 cycles); Detailed implementation manners

[0031] The invention will be further described below in conjunction with specific embodiments. It should be noted that the following embodiments are only used to illustrate the invention and do not limit the technical solutions described in the invention. Therefore, although the present specification has described the invention in detail with reference to the following embodiments, those skilled in the art should understand that the invention can still be modified or equivalently replaced; and all technical solutions and their improvements that do not depart from the spirit and scope of the invention should be covered within the scope of the claims of the invention.

[0032] Example 1

[0033] (1) A polyamic acid solution with a solid content of 15% in the BPDA / ODA system was synthesized in N,N-dimethylformamide solvent through condensation polymerization reaction. The nanofiber membrane was obtained by electrospinning and drying at 150 °C to remove the solvent. Similarly, the ODPA / ODA nanofiber membrane was obtained.

[0034] (2) The polyamic acid nanofibers of the BPDA / ODA system prepared above were impregnated in an aqueous solution of silver nitrate (AgNO3) with a concentration of 0.1 mol / L for silver ion exchange for 30 min, taken out, washed with deionized water and dried, and then impregnated in an aqueous solution of dimethylaminoborane (DMAB) with a concentration of 0.005 mol / L for silver ion reduction for 10 min, taken out, washed with deionized water and dried to obtain polyamic acid / silver composite nanofibers.

[0035] (3) The polyamic acid / silver composite nanofibers prepared above were dispersed in an aqueous solution of tert-butanol at a solid content of 1% (where the mass ratio of BPDA / ODA composite nanofibers to ODPA / ODA nanofibers is 9:1; the mass ratio of tert-butanol to water is 7:3). The dispersion was poured into a mold and prepared into a polyamic acid / silver composite nanofiber aerogel through freeze-drying. The polyamic acid / silver composite nanofiber aerogel was placed in a furnace (under a nitrogen atmosphere), heated from room temperature to 150 °C and held for 1.5 h, and then heated to 300 °C and held for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0036] (4) 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water were weighed and mixed to obtain solution A. 6 mL of ethanol, 2.1 g of glucose, 0.6 g of potassium sodium tartrate, and 60 mL of deionized water were weighed and mixed to obtain solution B. Solution A and solution B were mixed evenly to obtain an electroless plating solution.

[0037] (5) Immerse the prepared polyimide / silver composite nanofiber aerogel in the electroless plating solution for 30 min to obtain the polyimide / silver composite nanofiber aerogel.

[0038] Example 2

[0039] (1) Synthesize a polyamic acid solution of the BTDA / PDA system with a solid content of 15% in an N,N-dimethylformamide solvent through condensation polymerization. Remove the solvent by electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, obtain an ODPA / ODA nanofiber membrane.

[0040] (2) Immerse the prepared polyamic acid nanofibers of the BTDA / PDA system in an aqueous silver nitrate (AgNO3) solution with a concentration of 0.1 mol / L for silver ion exchange for 30 min. After taking out, wash and dry with deionized water, and then immerse in an aqueous solution of dimethylaminoborane (DMAB) with a concentration of 0.005 mol / L for silver ion reduction for 10 min. After taking out, wash and dry with deionized water to obtain polyamic acid / silver composite nanofibers.

[0041] (3) Disperse the prepared polyamic acid / silver composite nanofibers at a solid content of 1% in an aqueous tert-butanol solution (where the mass ratio of BTDA / PDA composite nanofibers to ODPA / ODA nanofibers is 9:1; the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid / silver composite nanofiber aerogel by freeze-drying. Place the polyamic acid / silver composite nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat from room temperature to 150 °C and hold for 1.5 h, then heat to 300 °C and hold for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0042] (4) Weigh 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water and mix to obtain solution A. Weigh 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water and mix to obtain solution B. Mix solution A and solution B evenly to obtain the electroless plating solution.

[0043] (5) Immerse the prepared polyimide / silver composite nanofiber aerogel in the electroless plating solution for 30 min to obtain a polyimide / silver composite nanofiber conductive aerogel.

[0044] Example 3

[0045] (1) A polyamic acid solution of the BPDA / ODA system with a solid content of 15% was synthesized in an N,N-dimethylformamide solvent through a condensation polymerization reaction. The solvent was removed by electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, a BPADA / MPD nanofiber membrane was obtained.

[0046] (2) The polyamic acid nanofibers of the BPDA / ODA system prepared above were immersed in an aqueous solution of silver nitrate (AgNO3) with a concentration of 0.1 mol / L for silver ion exchange for 30 min. After taking out, it was washed with deionized water and dried, and then immersed in an aqueous solution of dimethylaminoborane (DMAB) with a concentration of 0.005 mol / L for silver ion reduction for 10 min. After taking out, it was washed with deionized water and dried to obtain polyamic acid / silver composite nanofibers.

[0047] (3) The polyamic acid / silver composite nanofibers prepared above were dispersed in an aqueous solution of tert-butanol at a solid content of 1% (where the mass ratio of BPDA / ODA composite nanofibers to BPADA / MDA nanofibers is 9:1; the mass ratio of tert-butanol to water is 7:3). The dispersion was poured into a mold and freeze-dried to prepare a polyamic acid / silver composite nanofiber aerogel. The polyamic acid / silver composite nanofiber aerogel was placed in a furnace (under a nitrogen atmosphere), heated from room temperature to 150 °C and held for 1.5 h, and then heated to 300 °C and held for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0048] (4) 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water were weighed and mixed to obtain solution A. 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water were weighed and mixed to obtain solution B. Solution A and solution B were mixed evenly to obtain an electroless plating solution.

[0049] (5) The polyimide / silver composite nanofiber aerogel prepared above was immersed in the electroless plating solution for 30 min to obtain a polyimide / silver composite nanofiber aerogel.

[0050] Example 4

[0051] (1) A polyamic acid solution of the BPDA / ODA system with a solid content of 15% was synthesized in an N,N-dimethylformamide solvent through a condensation polymerization reaction. The solvent was removed by electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, an ODPA / ODA nanofiber membrane was obtained.

[0052] (2) The polyamic acid nanofibers of the BPDA / ODA system prepared above were immersed in an aqueous solution of silver nitrate (AgNO3) with a concentration of 0.05 mol / L for silver ion exchange for 30 min. After taking them out, they were washed with deionized water and dried, and then immersed in an aqueous solution of dimethylaminoborane (DMAB) with a concentration of 0.005 mol / L for silver ion reduction for 10 min. After taking them out, they were washed with deionized water and dried to obtain polyamic acid / silver composite nanofibers.

[0053] (3) The polyamic acid / silver composite nanofibers prepared above were dispersed in an aqueous solution of tert-butanol at a solid content of 1% (where the mass ratio of BPDA / ODA composite nanofibers to ODPA / ODA nanofibers was 9:1; the mass ratio of tert-butanol to water was 7:3). The dispersion was poured into a mold and freeze-dried to prepare a polyamic acid / silver composite nanofiber aerogel. The polyamic acid / silver composite nanofiber aerogel was placed in a hot furnace (under a nitrogen atmosphere), heated from room temperature to 150 °C and held for 1.5 h, and then heated to 300 °C and held for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0054] (4) Weigh 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water and mix them to obtain solution A. Weigh 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water and mix them to obtain solution B. Mix solution A and solution B evenly to obtain an electroless plating solution.

[0055] (5) Immerse the polyimide / silver composite nanofiber aerogel prepared above in the electroless plating solution for 30 min to obtain a polyimide / silver composite nanofiber aerogel.

[0056] Example 5

[0057] (1) A polyamic acid solution of the BPDA / ODA system with a solid content of 15% was synthesized in an N,N-dimethylformamide solvent through a condensation polymerization reaction. The solvent was removed by electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, an ODPA / ODA nanofiber membrane was obtained.

[0058] (2) The polyamic acid nanofibers of the BPDA / ODA system prepared above were immersed in an aqueous solution of silver nitrate (AgNO3) with a concentration of 0.2 mol / L for silver ion exchange for 30 min. After taking them out, they were washed with deionized water and dried, and then immersed in an aqueous solution of dimethylaminoborane (DMAB) with a concentration of 0.005 mol / L for silver ion reduction for 10 min. After taking them out, they were washed with deionized water and dried to obtain polyamic acid / silver composite nanofibers.

[0059] (3) Disperse the prepared polyamic acid / silver composite nanofibers obtained above at a solid content of 1% in an aqueous tert-butanol solution (where the mass ratio of BPDA / ODA composite nanofibers to ODPA / ODA nanofibers is 9:1; the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid / silver composite nanofiber aerogel through freeze-drying. Place the polyamic acid / silver composite nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat it from room temperature to 150 °C and hold for 1.5 h, then heat it to 300 °C and hold for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0060] (4) Weigh 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water and mix them to obtain solution A. Weigh 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water and mix them to obtain solution B. Mix solution A and solution B evenly to obtain an electroless plating solution.

[0061] (5) Immerse the prepared polyimide / silver composite nanofiber aerogel obtained above in the electroless plating solution for 30 min to obtain a polyimide / silver composite nanofiber aerogel.

[0062] Example 6

[0063] (1) Synthesize a polyamic acid solution of the BPDA / ODA system with a solid content of 15% in an N,N-dimethylformamide solvent through a condensation polymerization reaction. Remove the solvent through electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, obtain an ODPA / ODA nanofiber membrane.

[0064] (2) Immerse the prepared BPDA / ODA system polyamic acid nanofibers in an aqueous solution of silver trifluoromethanesulfonate (AgOTf) with a concentration of 0.1 mol / L for silver ion exchange for 30 min. Take it out, wash it with deionized water and dry it. Subsequently, immerse it in an aqueous solution of dimethylaminoborane (DMAB) with a concentration of 0.005 mol / L for silver ion reduction for 10 min. Take it out, wash it with deionized water and dry it to obtain polyamic acid / silver composite nanofibers.

[0065] (3) Disperse the obtained polyamic acid / silver composite nanofibers at a solid content of 1% in an aqueous tert-butanol solution (where the mass ratio of BPDA / ODA composite nanofibers to ODPA / ODA nanofibers is 9:1; the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid / silver composite nanofiber aerogel through freeze-drying. Place the polyamic acid / silver composite nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat it from room temperature to 150 °C and hold for 1.5 h, then heat it to 300 °C and hold for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0066] (4) Weigh 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water and mix them to obtain solution A. Weigh 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water and mix them to obtain solution B. Mix solution A and solution B evenly to obtain an electroless plating solution.

[0067] (5) Immerse the obtained polyimide / silver composite nanofiber aerogel in the electroless plating solution for 30 min to obtain a polyimide / silver composite nanofiber aerogel.

[0068] Example 7

[0069] (1) Synthesize a polyamic acid solution of the BPDA / ODA system with a solid content of 15% in an N,N-dimethylformamide solvent through condensation polymerization. Remove the solvent by electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, obtain an ODPA / ODA nanofiber membrane.

[0070] (2) Immerse the obtained BPDA / ODA system polyamic acid nanofibers in an aqueous solution of silver nitrate (AgNO3) with a concentration of 0.1 mol / L for silver ion exchange for 30 min. Take them out, wash them with deionized water, and dry them. Then immerse them in an aqueous solution of dimethylaminoborane (DMAB) with a concentration of 0.0025 mol / L for silver ion reduction for 10 min. Take them out, wash them with deionized water, and dry them to obtain polyamic acid / silver composite nanofibers.

[0071] (3) Disperse the prepared polyamic acid / silver composite nanofibers obtained above at a solid content of 1% in an aqueous tert-butanol solution (where the mass ratio of BPDA / ODA composite nanofibers to ODPA / ODA nanofibers is 9:1; the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid / silver composite nanofiber aerogel through freeze-drying. Place the polyamic acid / silver composite nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat it from room temperature to 150 °C and hold for 1.5 h, then heat it to 300 °C and hold for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0072] (4) Weigh 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water and mix them to obtain solution A. Weigh 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water and mix them to obtain solution B. Mix solution A and solution B evenly to obtain an electroless plating solution.

[0073] (5) Immerse the prepared polyimide / silver composite nanofiber aerogel obtained above in the electroless plating solution for 30 min to obtain a polyimide / silver composite nanofiber aerogel.

[0074] Example 8

[0075] (1) Synthesize a polyamic acid solution of the BPDA / ODA system with a solid content of 15% in an N,N-dimethylformamide solvent through a condensation polymerization reaction. Remove the solvent through electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, obtain an ODPA / ODA nanofiber membrane.

[0076] (2) Immerse the prepared BPDA / ODA system polyamic acid nanofibers in an aqueous solution of silver nitrate (AgNO3) with a concentration of 0.1 mol / L for silver ion exchange for 30 min. After taking them out, wash them with deionized water and dry them. Then immerse them in an aqueous solution of dimethylaminoborane (DMAB) with a concentration of 0.01 mol / L for silver ion reduction for 10 min. After taking them out, wash them with deionized water and dry them to obtain polyamic acid / silver composite nanofibers.

[0077] (3) Disperse the above-prepared polyamic acid / silver composite nanofibers at a solid content of 1% in an aqueous solution of tert-butanol (where the mass ratio of BPDA / ODA composite nanofibers to ODPA / ODA nanofibers is 9:1; the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid / silver composite nanofiber aerogel through freeze-drying. Place the polyamic acid / silver composite nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat it from room temperature to 150 °C and hold for 1.5 h, then heat it to 300 °C and hold for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0078] (4) Weigh 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water and mix them to obtain solution A. Weigh 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water and mix them to obtain solution B. Mix solution A and solution B evenly to obtain an electroless plating solution.

[0079] (5) Immerse the above-prepared polyimide / silver composite nanofiber aerogel in the electroless plating solution for 30 min to obtain a polyimide / silver composite nanofiber aerogel.

[0080] Example 9

[0081] (1) Synthesize a polyamic acid solution of the BPDA / ODA system with a solid content of 15% in an N,N-dimethylformamide solvent through condensation polymerization. Remove the solvent through electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, obtain an ODPA / ODA nanofiber membrane.

[0082] (2) Immerse the above-prepared polyamic acid nanofibers of the BPDA / ODA system in an aqueous solution of silver nitrate (AgNO3) with a concentration of 0.1 mol / L for silver ion exchange for 30 min. Take it out, wash it with deionized water, and dry it. Then immerse it in an aqueous solution of ascorbic acid with a concentration of 0.005 mol / L for silver ion reduction for 10 min. Take it out, wash it with deionized water, and dry it to obtain polyamic acid / silver composite nanofibers.

[0083] (3) Disperse the prepared polyamic acid / silver composite nanofibers obtained above at a solid content of 1% in an aqueous solution of tert-butanol (where the mass ratio of BPDA / ODA composite nanofibers to ODPA / ODA nanofibers is 9:1; the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid / silver composite nanofiber aerogel through freeze-drying. Place the polyamic acid / silver composite nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat it from room temperature to 150 °C and hold for 1.5 h, then heat it to 300 °C and hold for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0084] (4) Weigh 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water and mix them to obtain solution A. Weigh 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water and mix them to obtain solution B. Mix solution A and solution B evenly to obtain an electroless plating solution.

[0085] (5) Immerse the prepared polyimide / silver composite nanofiber aerogel obtained above in the electroless plating solution for 30 min to obtain a polyimide / silver composite nanofiber aerogel.

[0086] Example 10

[0087] (1) Synthesize a polyamic acid solution of the BPDA / ODA system with a solid content of 15% in an N,N-dimethylformamide solvent through a condensation polymerization reaction. Remove the solvent by electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, obtain an ODPA / ODA nanofiber membrane.

[0088] (2) Immerse the prepared polyamic acid nanofibers of the BPDA / ODA system in an aqueous solution of silver nitrate (AgNO3) with a concentration of 0.1 mol / L for silver ion exchange for 30 min. Take it out, wash it with deionized water and dry it, and then immerse it in an aqueous solution of dimethylaminoborane (DMAB) with a concentration of 0.005 mol / L for silver ion reduction for 10 min. Take it out, wash it with deionized water and dry it to obtain polyamic acid / silver composite nanofibers.

[0089] (3) Disperse the prepared polyamic acid / silver composite nanofibers obtained above at a solid content of 1% in an aqueous solution of tert-butanol (where the mass ratio of BPDA / ODA composite nanofibers to ODPA / ODA nanofibers is 6:1; the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid / silver composite nanofiber aerogel through freeze-drying. Place the polyamic acid / silver composite nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat it from room temperature to 150 °C and hold for 1.5 h, then heat it to 300 °C and hold for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0090] (4) Weigh 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water and mix them to obtain solution A. Weigh 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water and mix them to obtain solution B. Mix solution A and solution B evenly to obtain an electroless plating solution.

[0091] (5) Immerse the prepared polyimide / silver composite nanofiber aerogel obtained above in the electroless plating solution for 30 min to obtain a polyimide / silver composite nanofiber aerogel.

[0092] Example 11

[0093] (1) Synthesize a polyamic acid solution of the BPDA / ODA system with a solid content of 15% in an N,N-dimethylformamide solvent through a condensation polymerization reaction. Remove the solvent through electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, obtain an ODPA / ODA nanofiber membrane.

[0094] (2) Immerse the prepared BPDA / ODA system polyamic acid nanofibers in an aqueous solution of silver nitrate (AgNO3) with a concentration of 0.1 mol / L for silver ion exchange for 30 min. Take them out, wash them with deionized water, and dry them. Then immerse them in an aqueous solution of dimethylaminoborane (DMAB) with a concentration of 0.005 mol / L for silver ion reduction for 10 min. Take them out, wash them with deionized water, and dry them to obtain polyamic acid / silver composite nanofibers.

[0095] (3) Disperse the prepared polyamic acid / silver composite nanofibers obtained above at a solid content of 1% in an aqueous tert-butanol solution (where the mass ratio of BPDA / ODA composite nanofibers to ODPA / ODA nanofibers is 12:1; the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid / silver composite nanofiber aerogel through freeze-drying. Place the polyamic acid / silver composite nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat it from room temperature to 150 °C and hold for 1.5 h, then heat it to 300 °C and hold for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0096] (4) Weigh 1.5 g of silver nitrate, 9 ml of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water and mix them to obtain solution A. Weigh 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water and mix them to obtain solution B. Mix solution A and solution B evenly to obtain an electroless plating solution.

[0097] (5) Immerse the prepared polyimide / silver composite nanofiber aerogel obtained above in the electroless plating solution for 30 min to obtain a polyimide / silver composite nanofiber aerogel.

[0098] Example 12

[0099] (1) Synthesize a polyamic acid solution of the BPDA / ODA system with a solid content of 15% in an N,N-dimethylformamide solvent through a condensation polymerization reaction. Remove the solvent by electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, obtain an ODPA / ODA nanofiber membrane.

[0100] (2) Immerse the prepared BPDA / ODA system polyamic acid nanofibers in an aqueous solution of silver nitrate (AgNO3) with a concentration of 0.1 mol / L for silver ion exchange for 30 min. Take them out, wash them with deionized water, and dry them. Then immerse them in an aqueous solution of dimethylaminoborane (DMAB) with a concentration of 0.005 mol / L for silver ion reduction for 10 min. Take them out, wash them with deionized water, and dry them to obtain polyamic acid / silver composite nanofibers.

[0101] (3) Disperse the prepared polyamic acid / silver composite nanofibers obtained above at a solid content of 1% in an aqueous tert-butanol solution (where the mass ratio of BPDA / ODA composite nanofibers to ODPA / ODA nanofibers is 9:1; the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid / silver composite nanofiber aerogel through freeze-drying. Place the polyamic acid / silver composite nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat it from room temperature to 150 °C and hold for 1.5 h, then heat it to 300 °C and hold for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0102] (4) Weigh 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water and mix them to obtain solution A. Weigh 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water and mix them to obtain solution B. Mix solution A and solution B evenly to obtain an electroless plating solution.

[0103] (5) Immerse the prepared polyimide / silver composite nanofiber aerogel obtained above in the electroless plating solution for 20 min to obtain a polyimide / silver composite nanofiber aerogel.

[0104] Example 13

[0105] (1) Synthesize a polyamic acid solution of the BPDA / ODA system with a solid content of 15% in an N,N-dimethylformamide solvent through a condensation polymerization reaction. Remove the solvent by electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, obtain an ODPA / ODA nanofiber membrane.

[0106] (2) Immerse the prepared BPDA / ODA system polyamic acid nanofibers in an aqueous solution of silver nitrate (AgNO3) with a concentration of 0.1 mol / L for silver ion exchange for 30 min. Take them out, wash them with deionized water, and dry them. Then immerse them in an aqueous solution of dimethylaminoborane (DMAB) with a concentration of 0.005 mol / L for silver ion reduction for 10 min. Take them out, wash them with deionized water, and dry them to obtain polyamic acid / silver composite nanofibers.

[0107] (3) Disperse the prepared polyamic acid / silver composite nanofibers obtained above at a solid content of 1% in an aqueous tert-butanol solution (where the mass ratio of BPDA / ODA composite nanofibers to ODPA / ODA nanofibers is 9:1; the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid / silver composite nanofiber aerogel through freeze-drying. Place the polyamic acid / silver composite nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat it from room temperature to 150 °C and hold for 1.5 h, then heat it to 300 °C and hold for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0108] (4) Weigh 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water and mix them to obtain solution A. Weigh 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water and mix them to obtain solution B. Mix solution A and solution B evenly to obtain an electroless plating solution.

[0109] (5) Immerse the prepared polyimide / silver composite nanofiber aerogel obtained above in the electroless plating solution for 40 min to obtain a polyimide / silver composite nanofiber aerogel.

[0110] Comparative Example 1

[0111] (1) Synthesize a polyamic acid solution of the BPDA / ODA system with a solid content of 15% in an N,N-dimethylformamide solvent through a condensation polymerization reaction. Remove the solvent by electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, obtain an ODPA / ODA nanofiber membrane.

[0112] (2) Immerse the prepared polyamic acid nanofibers of the BPDA / ODA system in an aqueous solution of silver nitrate (AgNO3) with a concentration of 0.1 mol / L for silver ion exchange for 30 min. Take it out, wash it with deionized water and dry it. Then immerse it in an aqueous solution of dimethylaminoborane (DMAB) with a concentration of 0.005 mol / L for silver ion reduction for 10 min. Take it out, wash it with deionized water and dry it to obtain polyamic acid / silver composite nanofibers.

[0113] (3) Disperse the prepared polyamic acid / silver composite nanofibers obtained above at a solid content of 1% in an aqueous tert-butanol solution (where the mass ratio of BPDA / ODA composite nanofibers to ODPA / ODA nanofibers is 9:1; the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid / silver composite nanofiber aerogel through freeze-drying. Place the polyamic acid / silver composite nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat it from room temperature to 150 °C and hold for 1.5 h, then heat it to 300 °C and hold for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0114] Comparative Example 2

[0115] (1) Synthesize a polyamic acid solution of the BPDA / ODA system with a solid content of 15% in an N,N-dimethylformamide solvent through condensation polymerization. Remove the solvent through electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, obtain an ODPA / ODA nanofiber membrane.

[0116] (2) Disperse the prepared polyamic acid nanofibers obtained above at a solid content of 1% in an aqueous tert-butanol solution (where the mass ratio of BPDA / ODA nanofibers to ODPA / ODA nanofibers is 9:1; the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid nanofiber aerogel through freeze-drying. Place the polyamic acid nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat it from room temperature to 150 °C and hold for 1.5 h, then heat it to 300 °C and hold for 0.5 h to obtain a polyimide nanofiber aerogel.

[0117] (3) Weigh 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water and mix them to obtain solution A. Weigh 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water and mix them to obtain solution B. Mix solution A and solution B evenly to obtain an electroless plating solution.

[0118] (4) Immerse the prepared polyimide nanofiber aerogel obtained above in the electroless plating solution for 30 min to obtain a polyimide / silver composite nanofiber aerogel.

[0119] Comparative Example 3

[0120] (1) Synthesize a polyamic acid solution of the BPDA / ODA system with a solid content of 15% in an N,N-dimethylformamide solvent through condensation polymerization. Remove the solvent through electrospinning and drying at 150 °C to obtain a nanofiber membrane. Similarly, obtain an ODPA / ODA nanofiber membrane.

[0121] (2) Disperse the polyamic acid nanofibers prepared above at a solid content of 1% in an aqueous tert-butanol solution (where the mass ratio of BPDA / ODA nanofibers to ODPA / ODA nanofibers is 9:1; the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid nanofiber aerogel through freeze-drying. Place the polyamic acid nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat it from room temperature to 150 °C and hold for 1.5 h, then heat it to 300 °C and hold for 0.5 h to obtain a polyimide nanofiber aerogel.

[0122] (3) Mix nano silver powder and ethanol at a mass ratio of 1:25, and ultrasonically stir for 60 min at 25 °C to obtain an ethanol solution of nano silver.

[0123] (4) Immerse the polyimide nanofiber aerogel prepared above in the ethanol solution of nano silver for 30 min, then dry it at 50 °C for 3 h, and finally sinter the dried aerogel at 250 °C for 2 h to obtain a polyimide / silver nanofiber composite aerogel.

[0124] Comparative Example 4

[0125] (1) Synthesize a polyamic acid solution of the BPDA / ODA system with a solid content of 15% in an N,N-dimethylformamide solvent through condensation polymerization. Remove the solvent through electrospinning and drying at 150 °C to obtain a nanofiber membrane.

[0126] (2) Immerse the polyamic acid nanofibers of the BPDA / ODA system prepared above in an aqueous silver nitrate (AgNO3) solution with a concentration of 0.1 mol / L for silver ion exchange for 30 min. Take it out, wash it with deionized water and dry it, then immerse it in an aqueous dimethylaminoborane (DMAB) solution with a concentration of 0.005 mol / L for silver ion reduction for 10 min. Take it out, wash it with deionized water and dry it to obtain polyamic acid / silver composite nanofibers.

[0127] (3) Disperse the polyamic acid / silver composite nanofibers prepared above at a solid content of 1% in an aqueous tert-butanol solution (the mass ratio of tert-butanol to water is 7:3). Pour the dispersion into a mold and prepare a polyamic acid / silver composite nanofiber aerogel through freeze-drying. Place the polyamic acid / silver composite nanofiber aerogel in a furnace (under a nitrogen atmosphere), heat it from room temperature to 150 °C and hold for 1.5 h, then heat it to 300 °C and hold for 0.5 h to obtain a polyimide / silver composite nanofiber aerogel.

[0128] (4) Weigh 1.5 g of silver nitrate, 9 mL of ammonia water, 0.75 g of potassium hydroxide, and 90 mL of deionized water and mix them to obtain solution A. Weigh 6 mL of ethanol, 2.1 g of glucose, 0.6 g of sodium potassium tartrate, and 60 mL of deionized water and mix them to obtain solution B. Mix solution A and solution B evenly to obtain the electroless plating solution.

[0129] (5) Immerse the prepared polyimide / silver composite nanofiber aerogel in the electroless plating solution for 30 min to obtain the polyimide / silver composite nanofiber aerogel.

[0130] Piezoelectric performance test:

[0131] Resistance change rate @ 80% compressive strain = ((R0 - R) / R0) × 100%, where R0 is the resistance value of the sample without applied strain, and R is the resistance value of the sample under 80% applied strain;

[0132] Resistance increase rate @ 3000 - cycle compression = ((R 3000 - R0) / R0) × 100%, where R0 is the resistance value of the sample without applied strain, and R 3000 is the resistance value of the sample after 15% rebound after 3000 - cycle compression;

[0133] Rebound efficiency = (h / h0) × 100%, where h is the height of the sample after 80% compression and rebound, and h0 is the initial height of the sample.

[0134] Table 1 Resistance change rate @ 80% compressive strain, resistance increase rate @ 3000 - cycle compression, and rebound efficiency @ 1 min of the samples obtained under different examples and comparative examples

[0135]

[0136] As can be seen from Table 1, the aerogels of Comparative Example 1 with only the in - situ metallization step and Comparative Example 2 with only the electroless plating step do not have conductivity. Through Figure 2 the SEM images, it can be observed that the silver particles on the fiber surface of Comparative Example 1 are evenly dispersed but there are gaps between them; while in Example 1, the silver particles are closely combined to form a silver layer. This shows that the process of generating a silver seed layer on the fiber surface through in - situ metallization and then promoting the growth and connection of the silver seed layer to form a uniform silver layer through electroless plating can effectively transform the polyimide aerogel from non - conductive to conductive, providing value for its application in the field of flexible sensing.

[0137] Compared with Comparative Example 3 doped with silver nanoparticles, the resistance increase rate of the aerogel of Example 1 was smaller after 3000 cycles of compression. This indicates that the process combining in-situ metallization and electroless plating can improve the adhesion of silver nanoparticles in the composite aerogel, making it more stable than the direct doping method.

[0138] Compared with Comparative Example 4 without adding hot-melt polyimide nanofibers, the aerogel in Example 1 almost completely recovered after being compressed at 80% strain. This is because the hot-melt polyimide nanofibers can act as cross-linking agents in the fibers during the high-temperature thermal imidization process to form effective bonding, thereby enhancing the three-dimensional network skeleton structure of the aerogel and endowing the polyimide / silver composite nanofiber aerogel with excellent resilience.

[0139] In addition, as can be seen from Figure 1 the physical picture, the polyimide / silver composite nanofiber aerogel has good flexibility and can not break under high curling. Figure 3 shows the change rate of the resistance of the aerogel in response to strain. Figure 4 shows that the aerogel exhibits a stable response and a linear trend at different strains. Further, through Figure 5 the cyclic test of the resistance change rate, it can be seen that at 15% strain, after 3000 cycles of compression, the resistance change rate of the aerogel remains stable, showing excellent piezoresistive cyclic stability.

[0140] The above are only the preferred embodiments of the present invention, and do not limit the implementation manners and protection scope of the present invention. For those skilled in the art, it should be realized that all the equivalent substitutions and obvious changes made by using the description and drawings of the present invention should be included in the protection scope of the present invention.

Claims

1. A polyimide silver / composite nanofiber conductive aerogel with piezoresistive sensing performance, characterized in that, The polyimide nanofibers penetrate and crosslink with each other to form a three-dimensional nano-network skeleton, and silver nanoparticles are coated on the fiber surface, constituting a composite aerogel material with a three-dimensional conductive network structure; after the aerogel is compressed by 80% and recovered for 1 minute, the rebound efficiency of the aerogel is above 99%, and it has excellent rebound performance; it has an ultra-low linear detection limit (0.002 kPa, 0.5% compressive strain), and the resistance increase rate is less than 4% after repeated compression and rebound 3000 times or more at 15% strain, having a stable cyclic response ability.

2. The preparation method of the polyimide / silver composite nanofiber conductive aerogel with piezoresistive sensing performance according to claim 1, characterized in that, It includes the following steps: A: The diamine monomer and the dianhydride monomer are subjected to a polycondensation reaction to obtain a polyamic acid solution, and then subjected to electrospinning and further drying treatment to obtain polyamic acid nanofibers; according to the types of dianhydride and diamine monomers, thermosetting and hot-melt polyamic acid nanofibers can be respectively prepared; B: The thermosetting polyamic acid nanofibers prepared in step A are placed in an aqueous silver salt solution for ion exchange, and then placed in an aqueous reducing agent solution for reduction to form a silver seed layer on the surface of the polyamic acid nanofibers; C: The polyamic acid / silver composite nanofibers prepared in step B and the hot-melt nanofibers prepared in step A are dispersed in a specific solvent by high-speed stirring to obtain a nanofiber mixed dispersion, and then subjected to freeze-drying and thermal imidization treatment to obtain a polyimide / silver composite nanofiber aerogel with silver on the surface for the first time; D: Weigh an appropriate amount of silver salt and soluble base and dissolve them in deionized water, stir to obtain a clear and transparent mixed solution 1, and place it in the dark for later use; weigh an appropriate amount of alcohol auxiliary agent and weak reducing agent and dissolve them in deionized water, stir to obtain a clear and transparent mixed solution 2, and place it in the dark for later use; mix solution 1 and 2 and stir evenly to obtain an electroless plating solution, and place it in the dark for later use; E: The polyimide / silver composite nanofiber aerogel prepared in step C is placed in the electroless plating solution prepared in step D, taken out after impregnation for a period of time, washed and dried, and then the polyimide / silver composite nanofiber conductive aerogel with piezoresistive sensing performance is obtained.

3. The preparation method of a polyimide / silver composite nanofiber conductive aerogel with piezoresistive sensing performance according to claim 2, characterized in that, In step A, the solid content of the polyamic acid solution is 5-40 wt%; the drying treatment is drying at 150 °C for 0.5-3 h; the diameter of the polyimide nanofibers is 20-1000 nm, preferably 100-500 nm.

4. The preparation method of a polyimide / silver composite nanofiber conductive aerogel with piezoresistive sensing performance according to claim 2, characterized in that, The dianhydrides used in the preparation of the thermosetting polyimide nanofibers described in step A are one or a mixture of two or more of biphenyltetracarboxylic dianhydride (BPDA), pyromellitic dianhydride (PMDA), and benzophenone tetracarboxylic dianhydride (BTDA). The diamines are one or a mixture of two or more of diaminodiphenyl ether (ODA), p-phenylenediamine (PDA), and 4,4'-diaminodiphenylmethane (MDA). The dianhydrides used in the preparation of the thermoplastic polyimide nanofibers are one or a mixture of two or more of hexafluorodiacid dianhydride (6FDA), 4,4'-diphenylether tetracarboxylic dianhydride (ODPA), and bisphenol A type dianhydride (BPADA). The diamines are one or two of 4,4'-diaminodiphenyl ether (4,4'-ODA) and m-phenylenediamine (MPD). The solvents used are one or more of N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide.

5. The preparation method of a polyimide / silver composite nanofiber conductive aerogel with piezoresistive sensing performance according to claim 2, characterized in that, The silver salts described in step B are selected from one or more of silver chloride, silver cyanide, silver nitrate, silver acetate, silver fluoroborate, and silver trifluoromethanesulfonate. The solvent is deionized water. The solution concentration is 0.01 - 0.5 mol / L, the ion exchange time is 5 - 40 min, and the exchange temperature is 10 - 50 °C. The reducing agents are selected from one or more of formaldehyde, glucose, dimethylaminoborane, ascorbic acid, and sodium hypophosphite. The solvent is deionized water. The solution concentration is 1 - 20 mmol / L, the reduction time is 1 - 10 min, and the reduction temperature is 10 - 50 °C.

6. The preparation method of a polyimide / silver composite nanofiber conductive aerogel with piezoresistive sensing performance according to claim 2, characterized in that, The solid content of the dispersion described in step C is 0.5% - 3%. Among them, the mass ratio of the thermosetting composite nanofibers to the thermoplastic nanofibers is 6:1 - 12:

1. The solvent is an aqueous solution of tert-butanol, where the mass ratio of tert-butanol to water is 1:1 - 3:

1.

7. The preparation method of a polyimide / silver composite nanofiber conductive aerogel with piezoresistive sensing performance according to claim 2, characterized in that, The high-temperature thermal imidization process described in step C is as follows: Under a nitrogen atmosphere, it is heated from room temperature to 135 °C in 1 h and held for 0.5 h, and then heated to 300 °C in 1.5 h and held for 0.5 h.

8. The preparation method of a polyimide / silver composite nanofiber conductive aerogel with piezoresistive sensing performance according to claim 2, characterized in that The silver salts in the electroless plating solution described in step D are selected from one or more of silver chloride, silver cyanide, silver nitrate, silver acetate, silver fluoroborate, and silver trifluoromethanesulfonate. The soluble bases are selected from one or more of ammonia water, potassium hydroxide, and sodium hydroxide. The alcohol additives are selected from one or more of methanol, ethanol, n-propanol, and tert-butanol. The weak reducing agents are selected from one or more of glucose, glyoxal, formaldehyde, and potassium sodium tartrate.

9. The preparation method of a polyimide / silver composite nanofiber conductive aerogel with piezoresistive sensing performance according to claim 2, characterized in that, The soaking time of the polyimide / silver composite nanofiber aerogel in the electroless plating solution described in step E is 5 - 60 min, preferably 10 - 40 min.

10. A polyimide / silver composite nanofiber conductive aerogel and its products with piezoresistive sensing properties prepared by any of the methods according to claims 1 - 9.

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