A method for preparing a stretchable transparent electrode having helical conductive nanofibers and an electrode thereof

Abstract

This invention discloses a method for preparing a stretchable transparent electrode with helical conductive nanofibers. The method involves electrospinning a copolymer polyamic acid spinning solution onto a hollowed-out metal ring to form a pre-designed nanofiber network. The pre-designed nanofiber network is then heat-treated to obtain a nanofiber network with helicalized polyimide nanofibers. The nanofiber network is then immersed in a soluble silver salt solution for ion exchange, followed by chemical reduction with a reducing agent to obtain a silver-coated nanofiber network. This silver-coated nanofiber network undergoes a second silver coating to obtain a helical conductive polyimide nanofiber network. Finally, the helical conductive polyimide nanofiber network is transferred to the surface of a flexible transparent substrate to obtain the finished product. This invention also discloses an electrode prepared using a method for preparing a stretchable transparent electrode with helical conductive nanofibers. The stretchable transparent electrode prepared in this invention exhibits high transparency and maintains stable signal output over a wide strain range, showing great application potential in the field of flexible tensile sensors.

Description

Technical Field

[0001] This invention relates to the field of nanofiber technology, and in particular to a method for preparing a stretchable transparent electrode with helical conductive nanofibers and the electrode thereof. Background Technology

[0002] In recent years, emerging technologies such as electronic skin, wearable devices, flexible displays, and smart sensors have developed rapidly. Their thin, flexible, bendable, and even stretchable properties have brought revolutionary changes to fields such as medical monitoring, health management, motion tracking, and human-computer interaction. To ensure stable operation in complex and ever-changing practical applications, transparent electrodes, as one of their core functional components, must not only ensure excellent conductivity, optical transparency, and mechanical durability, but also be able to withstand elastic deformation.

[0003] Among numerous transparent conductive materials, conductive nanofiber networks have become an important candidate material for constructing stretchable transparent electrodes due to their high aspect ratio, excellent flexibility, and superior optical transmittance. However, they mainly rely on the relative slippage between the network nanostructures to alleviate strain. In practical applications, conductive nanofiber networks may experience a sharp decrease in electrode conductivity due to fiber breakage or failure of conductive paths during stretching, thus affecting the overall performance of the device. Therefore, how to improve the structural stability of conductive networks to achieve high conductivity of transparent electrodes under large strain conditions remains a key problem that urgently needs to be solved. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a stretchable transparent electrode with helical conductive nanofibers.

[0005] The innovation of this invention lies in the construction of a spiral conductive nanofiber with excellent repeated stretchability and bending fatigue resistance, and the preparation method of its stretchable transparent electrode. The prepared stretchable transparent electrode has high transparency and maintains stable signal output over a wide strain range, which has great application prospects in the field of flexible tensile sensors.

[0006] To achieve the above-mentioned objectives, the technical solution of this invention is: a method for preparing a stretchable transparent electrode with helical conductive nanofibers, comprising the following steps:

[0007] (1) A condensation polymerization reaction is carried out between a diamine monomer and a dianhydride monomer in an organic solvent to obtain a copolyamic acid spinning solution, wherein the diamine monomer and / or the dianhydride monomer includes monomers containing siloxane structures.

[0008] (2) The copolymer polyamic acid spinning solution is electrospinned and deposited on a hollow metal ring to form a pre-designed nanofiber network composed of several fibers.

[0009] (3) The preset nanofiber mesh is further heated to cause the fibers of the preset nanofiber mesh to undergo entropy elastic recovery curling, thereby obtaining a nanofiber mesh with helical polyimide nanofibers.

[0010] (4) The nanofiber mesh is treated with alkaline solution, then washed until neutral, placed in a soluble silver salt solution for ion exchange, and then chemically reduced by a reducing agent. An ultrathin seed silver layer is loaded on the surface of the spiral polyimide nanofibers of the nanofiber mesh to obtain a silver-coated nanofiber mesh.

[0011] (5) The silver-coated nanofiber mesh is immersed in a chemical plating solution for secondary silver coating to obtain a spiral conductive polyimide nanofiber mesh.

[0012] (6) The spiral conductive polyimide nanofiber mesh is transferred to the surface of a flexible transparent substrate by direct heating molding or by dispersion spin coating followed by heat treatment to obtain the finished product.

[0013] Further, in step (1), the molar ratio of dianhydride monomer to diamine monomer is 0.98–1.02:1, and the monomer containing the siloxane structure accounts for 5–100% of the total molar amount of diamine monomer and dianhydride monomer. The diamine monomer includes one or more of 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-diaminodiphenylmethane, 1,4-phenylenediamine, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, and 3,4-diaminobenzyloxytrifluoride. The dianhydride monomer includes hexafluoroisopropylphthalic anhydride, pyromellitic dianhydride, biphenyl dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 4,4-biphenyl ether dianhydride. One or more of 3,3,4,4-diphenylsulfone tetracarboxylic acid dianhydride and 4,4'-(3,4-dicarboxyphenoxy)diphenylthionine dianhydride; monomers containing a siloxane structure including aminopropyl-terminated polydimethylsiloxane, α,ω-bis(amino)-terminated polydimethylsiloxane, bis[4-(p-aminophenoxy)-phenoxy]dimethylsilane, 1,3-bis(γ-aminopropyl)-1,1′,3,3′-tetramethyldisiloxane, 1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldisiloxane dianhydride, and bis(3,4-benzenetetracarboxylic acid dianhydride)dimethylsilane; organic solvents including one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0014] Furthermore, the solid content of the copolyamic acid spinning solution is 5-40%.

[0015] Furthermore, in step (3), the heating temperature is 250–380°C and the treatment time is 0.5–2 h; the diameter of the spiral polyimide nanofibers is 50–500 nm.

[0016] Further, in step (4), the alkaline solution is an aqueous solution of potassium hydroxide and sodium hydroxide with a concentration of 0.02–0.2 mol / L and a treatment time of 5–90 min; the soluble silver salt solution contains one or more of silver nitrate, silver fluoride, silver fluoroborate, silver ammonia complex solution, and silver trifluoromethanesulfonate with a concentration of 0.01–1 g / ml and a treatment time of 1–60 min; the reducing agent contains one or more of glucose, dimethylaminoborane, ascorbic acid, and sodium hypophosphite with a concentration of 0.01–0.1 mol / L and a reduction time of 5–20 min.

[0017] Further, in step (5), the electroless plating solution includes solution A and solution B, with a volume ratio of 1 to 3:1. Solution A includes silver nitrate, ammonia, potassium hydroxide, and deionized water, while solution B includes glucose, potassium sodium tartrate, ethanol, and deionized water. Solution A: silver nitrate 10 to 20 g / L, ammonia 0.05 to 0.15 L / L, potassium hydroxide 5 to 15 g / L; Solution B: glucose 30 to 40 g / L, potassium sodium tartrate 5 to 15 g / L, ethanol 0.05 to 0.15 L / L; the immersion time in the electroless plating solution is 1 to 60 minutes.

[0018] Further, in step (6), the flexible transparent substrate is one of polydimethylsiloxane, polyimide, polyester, and polyvinyl alcohol; the heating temperature of the direct heating molding method is 5 to 50°C above the glass transition temperature of the flexible transparent substrate, the time is 0.5 to 5 minutes, and the pressure is 0.01 to 0.5 MPa; the method of heat treatment after dispersion spin coating is to first carry it at room temperature, and then heat it to above the glass transition temperature of the flexible transparent substrate.

[0019] A method for preparing a stretchable transparent electrode with helical conductive nanofibers reveals an electrode in which a helical conductive polyimide nanofiber mesh is attached to the surface of a flexible transparent substrate, wherein the fibers of the helical conductive polyimide nanofiber mesh are formed by coating the surface of helical polyimide nanofibers with a silver layer.

[0020] The beneficial effects of this invention are:

[0021] 1. This invention introduces flexible siloxane segments into the molecular backbone structure (i.e., adds monomers containing siloxane structures during polymerization), which enables polyamic acid nanofibers to become highly helical during high-temperature heat treatment, resulting in superior repeated stretchability and resistance to bending fatigue compared to traditional nanofiber networks.

[0022] 2. The method of the present invention forms a pre-set nanofiber network by directly depositing on a hollow metal ring. The polyamic acid nanofibers are imidized while being spiralized at high temperature, and then further silvered on the surface to form a conductive network. It has the advantage of integrated molding and does not damage the original conductive network structure during post-processing.

[0023] 3. The method of the present invention first performs ring-opening treatment on the surface of polyimide nanofibers by alkaline treatment to generate -COO- active groups, and then performs chemical silver plating on the surface of nanofibers. The silver layer and the nanofiber substrate have stronger adhesion, and the prepared stretchable transparent electrode still has excellent cycle stability under large tensile strain conditions.

[0024] 4. The method of the present invention bonds helical conductive nanofibers to the surface of a flexible transparent substrate by direct heating molding or dispersion spin coating heat treatment, which completely preserves the original polyimide nanofiber conductive network structure. At the same time, the nanofibers and the flexible transparent substrate have good adhesion, and can maintain stable signal output during repeated stretching and bending. Attached Figure Description

[0025] Figure 1 This is a photograph of the stretchable transparent electrode prepared in Example 1.

[0026] Figure 2 This is an SEM image of the nanofiber network with spiral polyimide nanofibers obtained in step (3) of Example 1.

[0027] Figure 3 This is a SEM image of the stretchable transparent electrode prepared in Example 1.

[0028] Figure 4 These are the XRD patterns of the stretchable transparent electrode prepared in Example 1 before and after silver plating.

[0029] Figure 5 It is the resistance change rate of the stretchable transparent electrode prepared in Example 1 under different tensile strains.

[0030] Figure 6 The resistance change rate of the stretchable transparent electrode prepared in Example 1 is shown in (a) tensile cycle response test under different tensile strains and (b) resistance change rate after 100 tensile cycles at 40% tensile strain.

[0031] Figure 7 This is a comparison of the resistance change rate of the stretchable transparent electrode prepared in Example 1 and the commercially available ITO transparent conductive electrode after being repeatedly bent 2000 times at (a) different bending radii and (b) a bending radius of 2 mm. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will now be clearly and completely described in conjunction with the accompanying drawings.

[0033] Example 1: A method for preparing a stretchable transparent electrode with helical conductive nanofibers, comprising the following steps:

[0034] (1) A condensation polymerization reaction is carried out between a diamine monomer and a dianhydride monomer in an organic solvent to obtain a copolyamic acid spinning solution. The diamine monomer and / or the dianhydride monomer includes a monomer containing a siloxane structure. The solid content of the copolyamic acid spinning solution is 5%. The molar ratio of the dianhydride monomer to the diamine monomer is 0.98:1. The monomer containing a siloxane structure accounts for 5% of the total molar amount of the diamine monomer and the dianhydride monomer. The diamine monomer is 4,4'-diaminodiphenyl ether. The dianhydride monomer is hexafluoroisopropylphthalic anhydride. The monomer containing a siloxane structure is aminopropyl-terminated polydimethylsiloxane. The organic solvent is N,N-dimethylformamide.

[0035] (2) The copolymer polyamic acid spinning solution is electrospinned and deposited on a hollow metal ring to form a pre-designed nanofiber network composed of several fibers.

[0036] (3) The preset nanofiber mesh is further heated to cause the fibers of the preset nanofiber mesh to undergo entropy elastic recovery and coiling, so as to obtain a nanofiber mesh with helical polyimide nanofibers; the heating temperature is 250℃ and the treatment time is 0.5h; the diameter of the helical polyimide nanofibers is 500nm.

[0037] (4) The nanofiber mesh was treated with an alkaline solution, then washed until neutral, and placed in a soluble silver salt solution for ion exchange. After chemical reduction with a reducing agent, an ultrathin seed silver layer was loaded on the surface of the spiral polyimide nanofibers of the nanofiber mesh to obtain a silver-coated nanofiber mesh. The alkaline solution was an aqueous solution of potassium hydroxide with a concentration of 0.02 mol / L and a treatment time of 5 min. The silver salt in the soluble silver salt solution was silver nitrate with a concentration of 0.01 g / ml and a treatment time of 1 min. The reducing agent was glucose with a concentration of 0.01 mol / L and a reduction time of 5 min.

[0038] (5) The silver-coated nanofiber mesh is immersed in a chemical plating solution for secondary silver plating to obtain a spiral conductive polyimide nanofiber mesh; the chemical plating solution includes solution A and solution B, with a volume ratio of 1:1. Solution A includes silver nitrate, ammonia, potassium hydroxide and deionized water, and solution B includes glucose, potassium sodium tartrate, ethanol and deionized water. Solution A: silver nitrate 10 g / L, ammonia 0.05 L / L, potassium hydroxide 5 g / L; Solution B: glucose 30 g / L, potassium sodium tartrate 5 g / L, ethanol 0.05 L / L;

[0039] Immersion time in the chemical plating solution is 1 minute.

[0040] (6) The spiral conductive polyimide nanofiber mesh is transferred to the surface of a flexible transparent substrate by direct heating molding to obtain the finished product; the flexible transparent substrate is polydimethylsiloxane; the heating temperature of the direct heating molding method is 5°C above the glass transition temperature of the flexible transparent substrate, and the time is...

[0041] 0.5 min, pressure 0.01 MPa.

[0042] Example 2: A method for preparing a stretchable transparent electrode with helical conductive nanofibers, comprising the following steps:

[0043] (1) A condensation polymerization reaction is carried out between a diamine monomer and a dianhydride monomer in an organic solvent to obtain a copolyamic acid spinning solution. The diamine monomer and / or the dianhydride monomer includes a monomer containing a siloxane structure. The solid content of the copolyamic acid spinning solution is 20%. The molar ratio of the dianhydride monomer to the diamine monomer is 1:1. The monomer containing a siloxane structure accounts for 40% of the total molar amount of the diamine monomer and the dianhydride monomer. The diamine monomer is 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl. The dianhydride monomer is pyromellitic dianhydride. The monomer containing a siloxane structure is α,ω-bis(amino)-terminated polydimethylsiloxane. The organic solvent is N,N-dimethylacetamide.

[0044] (2) The copolymer polyamic acid spinning solution is electrospinned and deposited on a hollow metal ring to form a pre-designed nanofiber network composed of several fibers.

[0045] (3) The preset nanofiber mesh is further heated to cause the fibers of the preset nanofiber mesh to undergo entropy elastic recovery curling, thereby obtaining a nanofiber mesh with helical polyimide nanofibers; the heating temperature is 250℃ and the treatment time is 0.5h; the diameter of the helical polyimide nanofibers is 50nm.

[0046] (4) The nanofiber mesh was treated with an alkaline solution, then washed until neutral, and placed in a soluble silver salt solution for ion exchange. After chemical reduction with a reducing agent, an ultrathin seed silver layer was loaded on the surface of the spiral polyimide nanofibers of the nanofiber mesh to obtain a silver-coated nanofiber mesh. The alkaline solution was an aqueous solution of sodium hydroxide with a concentration of 0.1 mol / L and a treatment time of 40 min. The silver salt in the soluble silver salt solution was silver fluoride with a concentration of 0.05 g / ml and a treatment time of 30 min. The reducing agent was dimethylaminoborane with a concentration of 0.05 mol / L and a reduction time of 10 min.

[0047] (5) The silver-coated nanofiber mesh is immersed in a chemical plating solution for secondary silver plating to obtain a spiral conductive polyimide nanofiber mesh; the chemical plating solution includes solution A and solution B, with a volume ratio of solution A to solution B of 2:1. Solution A includes silver nitrate, ammonia, potassium hydroxide and deionized water, and solution B includes glucose, potassium sodium tartrate, ethanol and deionized water. Solution A: silver nitrate 12g / L, ammonia 0.08L / L, potassium hydroxide 8g / L; Solution B: glucose 33g / L, potassium sodium tartrate 8g / L, ethanol 0.08L / L;

[0048] Immersion time in the chemical plating solution is 20 minutes.

[0049] (6) The spiral conductive polyimide nanofiber mesh is directly heated and molded to obtain the finished product; the flexible transparent substrate is polyimide; the heating temperature of the direct heating and molding method is 25°C above the glass transition temperature of the flexible transparent substrate, the time is 2 min, and the pressure is 0.02 MPa.

[0050] Example 3: A method for preparing a stretchable transparent electrode with helical conductive nanofibers, comprising the following steps:

[0051] (1) A condensation polymerization reaction is carried out between a diamine monomer and a dianhydride monomer in an organic solvent to obtain a copolymer polyamic acid spinning solution. The diamine monomer and / or the dianhydride monomer includes a monomer containing a siloxane structure. The solid content of the copolymer polyamic acid spinning solution is 40%. The molar ratio of the dianhydride monomer to the diamine monomer is 1.01:1. The monomer containing a siloxane structure accounts for 60% of the total molar amount of the diamine monomer and the dianhydride monomer. The diamine monomer is 4,4'-diaminodiphenylmethane. The dianhydride monomer is biphenyl dianhydride. The monomer containing a siloxane structure is bis[4-(p-aminophenoxy)-phenoxy]dimethylsilane. The organic solvent is N-methylpyrrolidone.

[0052] (2) The copolymer polyamic acid spinning solution is electrospinned and deposited on a hollow metal ring to form a pre-designed nanofiber network composed of several fibers.

[0053] (3) The preset nanofiber mesh is further heated to cause the fibers of the preset nanofiber mesh to undergo entropy elastic recovery and coiling, so as to obtain a nanofiber mesh with helical polyimide nanofibers; the heating temperature is 380℃ and the treatment time is 2h; the diameter of the helical polyimide nanofibers is 500nm.

[0054] (4) The nanofiber mesh was treated with an alkaline solution, then washed until neutral, and placed in a soluble silver salt solution for ion exchange. After chemical reduction with a reducing agent, an ultrathin seed silver layer was loaded on the surface of the spiral polyimide nanofibers of the nanofiber mesh to obtain a silver-coated nanofiber mesh. The alkaline solution was an aqueous solution of potassium hydroxide with a concentration of 0.2 mol / L and a treatment time of 90 min. The silver salt in the soluble silver salt solution was silver fluoroborate with a concentration of 1 g / ml and a treatment time of 60 min. The reducing agent was ascorbic acid with a concentration of 0.1 mol / L and a reduction time of 20 min.

[0055] (5) The silver-coated nanofiber mesh is immersed in a chemical plating solution for secondary silver plating to obtain a spiral conductive polyimide nanofiber mesh; the chemical plating solution includes solution A and solution B, with a volume ratio of solution A to solution B of 2.5:1. Solution A includes silver nitrate, ammonia, potassium hydroxide and deionized water, and solution B includes glucose, potassium sodium tartrate, ethanol and deionized water. Solution A: silver nitrate 17 g / L, ammonia 0.12 L / L, potassium hydroxide 13 g / L; Solution B: glucose 38 g / L, potassium sodium tartrate 12 g / L, ethanol 0.12 L / L;

[0056] Immersion time in the chemical plating solution is 40 minutes.

[0057] (6) The spiral conductive polyimide nanofiber mesh is transferred to the surface of a flexible transparent substrate by direct heating molding to obtain the finished product; the flexible transparent substrate is polyester; the heating temperature of the direct heating molding method is 50°C above the glass transition temperature of the flexible transparent substrate, the time is 5 min, and the pressure is 0.5 MPa.

[0058] Example 4: A method for preparing a stretchable transparent electrode with helical conductive nanofibers, comprising the following steps:

[0059] (1) A condensation polymerization reaction is carried out between diamine monomer and dianhydride monomer in an organic solvent to obtain a copolymer polyamic acid spinning solution. The diamine monomer and / or dianhydride monomer includes monomers containing siloxane structures. The solid content of the copolymer polyamic acid spinning solution is 35%. The molar ratio of dianhydride monomer to diamine monomer is 1.02:1. The monomers containing siloxane structures account for 100% of the total molar amount of diamine monomer and dianhydride monomer. The monomers containing siloxane structures are aminopropyl-terminated polydimethylsiloxane and bis(3,4-benzenetetracarboxylic acid dianhydride)dimethylsilane. The organic solvent is N,N-dimethylformamide.

[0060] (2) The copolymer polyamic acid spinning solution is electrospinned and deposited on a hollow metal ring to form a pre-designed nanofiber network composed of several fibers.

[0061] (3) The preset nanofiber mesh is further heated to cause the fibers of the preset nanofiber mesh to undergo entropy elastic recovery curling, thereby obtaining a nanofiber mesh with helical polyimide nanofibers; the heating temperature is 350℃ and the treatment time is 1.5h; the diameter of the helical polyimide nanofibers is 350nm.

[0062] (4) The nanofiber mesh was treated with an alkaline solution, then washed until neutral, and placed in a soluble silver salt solution for ion exchange. After chemical reduction with a reducing agent, an ultrathin seed silver layer was loaded on the surface of the spiral polyimide nanofibers of the nanofiber mesh to obtain a silver-coated nanofiber mesh. The alkaline solution was an aqueous solution of sodium hydroxide with a concentration of 0.05 mol / L and a treatment time of 35 min. The silver salt in the soluble silver salt solution was silver trifluoromethanesulfonate with a concentration of 0.08 g / ml and a treatment time of 50 min. The reducing agent was sodium hypophosphite with a concentration of 0.08 mol / L and a reduction time of 15 min.

[0063] (5) The silver-coated nanofiber mesh is immersed in a chemical plating solution for secondary silver plating to obtain a spiral conductive polyimide nanofiber mesh; the chemical plating solution includes solution A and solution B, with a volume ratio of solution A to solution B of 3:1. Solution A includes silver nitrate, ammonia, potassium hydroxide and deionized water, and solution B includes glucose, potassium sodium tartrate, ethanol and deionized water. Solution A: silver nitrate 20 g / L, ammonia 0.15 L / L, potassium hydroxide 15 g / L; Solution B: glucose 40 g / L, potassium sodium tartrate 15 g / L, ethanol 0.15 L / L;

[0064] Immersion time in the chemical plating solution is 60 minutes.

[0065] (6) The spiral conductive polyimide nanofiber mesh is transferred to the surface of a flexible transparent substrate by a method of dispersion spin coating followed by heat treatment to obtain the finished product; the flexible transparent substrate is polyvinyl alcohol; the method of dispersion spin coating followed by heat treatment is carried out at room temperature first, and then heated to above the glass transition temperature of the flexible transparent substrate.

[0066] Example 5: Referring to Example 1, the diamine monomer includes one or more of 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-diaminodiphenylmethane, 1,4-phenylenediamine, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, and 3,4-diaminobenzyloxytrifluoride; the dianhydride monomer includes hexafluoroisopropylphthalic anhydride, pyromellitic dianhydride, biphenyl dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4-biphenyl ether dianhydride, 3,3,4,4-diphenylsulfone tetracarboxylic dianhydride, and 4,4'-(3,4- One or more of dicarboxyphenoxy-diphenylthionine dianhydride; monomers containing a siloxane structure including aminopropyl-terminated polydimethylsiloxane, α,ω-bis(amino)-terminated polydimethylsiloxane, bis[4-(p-aminophenoxy)-phenoxy]dimethylsilane, 1,3-bis(γ-aminopropyl)-1,1′,3,3′-tetramethyldisiloxane, 1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldisiloxane dianhydride, and bis(3,4-benzenetetracarboxylic dianhydride)dimethylsilane; organic solvents including one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

[0067] The silver salt in the soluble silver salt solution includes one or more of silver nitrate, silver fluoride, silver fluoroborate, silver ammonia complex solution, and silver trifluoromethanesulfonate; the reducing agent includes one or more of glucose, dimethylaminoborane, ascorbic acid, and sodium hypophosphite.

[0068] Flexible transparent substrates include one of polydimethylsiloxane, polyimide, polyester, and polyvinyl alcohol.

[0069] Example 6: An electrode prepared by a method for fabricating a stretchable transparent electrode with helical conductive nanofibers. The electrode is prepared by attaching a helical conductive polyimide nanofiber mesh to the surface of a flexible transparent substrate. The fibers of the helical conductive polyimide nanofiber mesh are formed by coating a silver layer on the surface of helical polyimide nanofibers.

[0070] Comparative Example 1: Referring to Example 1, the monomer containing the siloxane structure accounts for 0% of the total molar amount of the diamine monomer and dianhydride monomer.

[0071] Comparative Example 2: Referring to Example 1, the silver plating method in steps (4) and (5) was modified to "vacuum evaporation method to plate silver on a nanofiber mesh with spiral polyimide nanofibers to obtain a spiral conductive polyimide nanofiber mesh".

[0072] Comparative Example 3: Referring to Example 1, the phrase "the copolyamic acid spinning solution is electrospinned on a hollow metal ring to form a preset nanofiber network composed of several fibers" in steps (2) and (3) is modified to "the preset nanofiber network is deposited on aluminum foil by electrospinning".

[0073] Table 1. Initial sheet resistance, sheet resistance under 40% tensile strain, and sheet resistance under 100 tensile cycles at 40% tensile strain for the stretchable transparent electrodes prepared in different embodiments and comparative examples.

[0074]

[0075] As can be seen from Examples 1-4 and Comparative Examples 1-3 in Table 1, the stretchable transparent electrode prepared by the method of the present invention has good conductivity, and the sheet resistance change rate is extremely small after large tensile deformation and multiple tensile cycle tests, indicating that it has good stretchability and fatigue resistance. Comparing the sheet resistance and sheet resistance change of Example 1 and Comparative Example 1, it can be seen that the introduction of siloxane segments can make the nanofibers highly helicalized during heat treatment. Therefore, the sheet resistance of the prepared stretchable transparent electrode remains almost unchanged after large tensile deformation and multiple cycle tests. In addition, the comparison of the sheet resistance change results of Example 1 and Comparative Example 2 shows that the silver plating method provided by the present invention results in a stronger adhesion between the silver layer and the nanofiber matrix.

[0076] Figure 1 The image shows a physical picture of a stretchable transparent electrode prepared using the method of this invention. It can be seen that the prepared electrode has good transparency and conductivity. Figure 2 , Figure 3 and Figure 4 SEM images and XRD patterns of the nanofibers before and after silver plating show that they are highly spiralized and their surfaces are completely coated with silver nanoparticles. Figure 5 , Figure 6 and Figure 7 The tensile and bending tests demonstrate that the transparent electrode prepared by the method of the present invention has better cycle stability under large tensile strain and bending conditions compared with the prior art.

[0077] The described embodiments 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 of making a stretchable transparent electrode having helical conductive nanofibers, characterized by, Includes the following steps: (1) The diamine monomer and the dianhydride monomer are subjected to a condensation polymerization reaction in an organic solvent to obtain a copolyamic acid spinning solution. The diamine monomer and / or the dianhydride monomer includes a monomer containing a siloxane structure. The monomer containing a siloxane structure includes one or more of the following: aminopropyl-terminated polydimethylsiloxane, α,ω-bis(amino)-terminated polydimethylsiloxane, bis[4-(p-aminophenoxy)-phenoxy]dimethylsilane, 1,3-bis(γ-aminopropyl)-1,1′,3,3′-tetramethyldisiloxane, 1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldisiloxane dianhydride, and bis(3,4-benzenetetracarboxylic dianhydride)dimethylsilane. (2) The copolymer polyamic acid spinning solution is electrospinned and deposited on a hollow metal ring to form a pre-designed nanofiber network composed of several fibers. (3) The preset nanofiber mesh is further heated to cause the fibers of the preset nanofiber mesh to undergo entropy elastic recovery coiling, thereby obtaining a nanofiber mesh with helicalized polyimide nanofibers; (4) The nanofiber mesh is treated with alkaline solution, then washed until neutral, placed in a soluble silver salt solution for ion exchange, and then chemically reduced by a reducing agent. An ultrathin seed silver layer is loaded on the surface of the spiral polyimide nanofibers of the nanofiber mesh to obtain a silver-coated nanofiber mesh. (5) The silver-coated nanofiber mesh is immersed in a chemical plating solution for secondary silver coating to obtain a spiral conductive polyimide nanofiber mesh. (6) The spiral conductive polyimide nanofiber mesh is transferred to the surface of a flexible transparent substrate by direct heating molding or by dispersion spin coating followed by heat treatment to obtain the finished product.

2. The method of claim 1, wherein the method further comprises the step of: In step (1), the molar ratio of dianhydride monomer to diamine monomer is 0.98–1.02:1, and the monomer containing a siloxane structure accounts for 5–100% of the total molar amount of diamine monomer and dianhydride monomer. The diamine monomer includes 4,4'-diaminodiphenyl ether, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-diaminodiphenylmethane, 1,4-phenylenediamine, 2,2-bis[4-(4-aminophenoxy)phenyl]-1,1,1,3,3,3-hexafluoropropane, 3,4- One or more of diaminobenzyloxytrifluorides; dianhydride monomers include one or more of hexafluoroisopropylphthalic anhydride, pyromellitic dianhydride, biphenyl dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4-biphenyl ether dianhydride, 3,3,4,4-diphenylsulfone tetracarboxylic dianhydride, and 4,4'-(3,4-dicarboxyphenoxy)diphenylthionine dianhydride; organic solvents include one or more of N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone.

3. The method of claim 1, wherein the method further comprises the step of: The solid content of the copolymer polyamic acid spinning solution is 5-40%.

4. The method for preparing a stretchable transparent electrode with helical conductive nanofibers according to claim 1, characterized in that, The heating temperature in step (3) is 250-380℃ and the treatment time is 0.5-2h; the diameter of the spiral polyimide nanofiber is 50-500nm.

5. The method for preparing a stretchable transparent electrode with helical conductive nanofibers according to claim 1, characterized in that, The alkaline solution in step (4) is an aqueous solution of potassium hydroxide and sodium hydroxide with a concentration of 0.02-0.2 mol / L and a treatment time of 5-90 min; the soluble silver salt solution contains one or more of silver nitrate, silver fluoride, silver fluoroborate, silver ammonia complex solution, and silver trifluoromethanesulfonate with a concentration of 0.01-1 g / ml and a treatment time of 1-60 min; the reducing agent contains one or more of glucose, dimethylaminoborane, ascorbic acid, and sodium hypophosphite with a concentration of 0.01-0.1 mol / L and a reduction time of 5-20 min.

6. The method for preparing a stretchable transparent electrode with helical conductive nanofibers according to claim 1, characterized in that, In step (5), the electroless plating solution includes solution A and solution B, with a volume ratio of 1 to 3:

1. Solution A includes silver nitrate, ammonia, potassium hydroxide, and deionized water, while solution B includes glucose, potassium sodium tartrate, ethanol, and deionized water. Solution A: silver nitrate 10 to 20 g / L, ammonia 0.05 to 0.15 L / L, potassium hydroxide 5 to 15 g / L; Solution B: glucose 30 to 40 g / L, potassium sodium tartrate 5 to 15 g / L, ethanol 0.05 to 0.15 L / L; the immersion time in the electroless plating solution is 1 to 60 minutes.

7. The method for preparing a stretchable transparent electrode with helical conductive nanofibers according to claim 1, characterized in that, In step (6), the flexible transparent substrate is one of polydimethylsiloxane, polyimide, polyester, or polyvinyl alcohol; the heating temperature of the direct heating molding method is 5 to 50°C above the glass transition temperature of the flexible transparent substrate, the time is 0.5 to 5 minutes, and the pressure is 0.01 to 0.5 MPa; the method of heat treatment after dispersion spin coating is to first carry it out at room temperature, and then heat it to above the glass transition temperature of the flexible transparent substrate.

8. An electrode prepared by the method for preparing a stretchable transparent electrode with helical conductive nanofibers as described in any one of claims 1 to 7, characterized in that, A spiral conductive polyimide nanofiber mesh is attached to the surface of a flexible transparent substrate. The fibers of the spiral conductive polyimide nanofiber mesh are formed by coating the surface of spiral polyimide nanofibers with a silver layer.

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