CN112331410B

CN112331410B - Preparation of silver nanowire and application of silver nanowire in transparent conductive film

Info

Publication number: CN112331410B
Application number: CN202010928296.9A
Authority: CN
Inventors: 胡家文; 韩梅; 段曦东; 葛勇杰
Original assignee: Hunan University
Current assignee: Hunan University
Priority date: 2020-09-07
Filing date: 2020-09-07
Publication date: 2021-11-26
Anticipated expiration: 2040-09-07
Also published as: CN112331410A

Abstract

The invention provides a preparation method of a silver nanowire and application of the silver nanowire in a transparent conductive film, wherein the preparation method of the silver nanowire comprises the following steps: step 1): obtaining a composite hydrogel comprising NVP polymerized linear and branched polymers; step 2): dissolving the composite hydrogel and a control agent in polyhydric alcohol to obtain a base solution, then adding a silver source solution A into the base solution, carrying out pre-reaction, and synthesizing a nano-silver seed crystal solution; step 3): and (3) dropwise adding the silver source solution B into the nano silver seed crystal solution obtained in the step 2), and continuing to react to obtain the silver nanowires. The silver nanowire transparent film prepared by the invention has high light transmittance and good conductivity, and is beneficial to the implementation of industrial production.

Description

Preparation of silver nanowire and application of silver nanowire in transparent conductive film

Technical Field

The invention relates to the technical field of flexible transparent conductive films, in particular to preparation of a high-length-diameter-ratio, high-purity and ultrathin capping layer silver nanowire and application of the capping layer silver nanowire in a transparent conductive film.

Background

As mobile internet technology and artificial intelligence devices have penetrated every corner of the world, transparent conductive electrodes, which play an important role in electronic devices, have attracted great research interest. Most of the transparent electrodes are currently producedThe technique is based on metal oxides, e.g. In₂O₃:Sn(ITO)，SnO₂F (FTO), ZnO (Al (AZO)), which have very good light transmission and very low electrical resistivity. However, there are many problems, such as low storage capacity, high manufacturing cost, complex process, and its mechanical property is very poor, which greatly hinders the application in flexible optoelectronic devices. In order to solve these problems, researchers have searched for a series of alternative materials, in which silver nanowires (silver nanowires) are considered as ideal materials for the next generation of flexible Transparent Conductors (TCs) because of their advantages of bending resistance, high optical transparency, good electrical and thermal conductivity, and the like.

The length-diameter ratio of the silver nanowire is one of the influence factors of the conductivity and the transmittance of the transparent conductive film of the silver nanowire. Currently, researchers have developed many synthetic methods for synthesizing silver nanowires (Ag NWs) with controllable morphology and aspect ratio, including ultraviolet radiation method, template method, hydrothermal method, electrochemical method and polyol reduction method. The polyol method is simple to operate, low in cost and capable of realizing mass production, and is a mature method for preparing the silver nanowires with high length-diameter ratio at present.

However, the end capping agent is introduced into the silver nanowire product prepared by the polyol method, which inevitably results in an insulating end capping agent layer remaining on the surface of the silver nanowire and cannot be removed by the conventional washing process. The presence of the capping layer can create a barrier to electron transport between nanowires and at the AgNW film/active layer of the stacked device constructed from AgNW films, thereby greatly affecting the in-plane and out-of-plane carrier transport properties of the transparent conductive thin film. In addition, the synthesis process is easy to generate more silver nano particle (Ag NPs) by-products. Because Ag NPs have a strong light scattering effect, the light transmittance of the Ag NW film is greatly influenced, raw materials are seriously wasted and are difficult to remove, a subsequent complex purification treatment process is required, and the overall yield of the silver nanowires is reduced.

Disclosure of Invention

In order to solve the defects of small length-diameter ratio, low purity, thick end-capping film, non-ideal photoelectric property and the like of the prepared material in the existing silver nanowire preparation method, the first aim of the invention is to provide a method for preparing the ultrathin end-capping layer silver nanowire with high length-diameter ratio and high purity.

The second purpose of the invention is to provide the silver nanowire prepared by the preparation method.

The third purpose of the invention is to provide a transparent conductive film containing the silver nanowires.

The fourth purpose of the invention is to provide the application of the transparent conductive film in preparing electronic and/or photoelectric devices.

A preparation method of silver nanowires comprises the following steps:

step 1): obtaining a composite hydrogel comprising NVP polymerized linear and branched polymers;

step 2): dissolving the composite hydrogel and a control agent in polyhydric alcohol to obtain a base solution, then adding a silver source solution A into the base solution, carrying out pre-reaction, and synthesizing a nano-silver seed crystal solution;

step 3): and (3) dropwise adding the silver source solution B into the nano silver seed crystal solution obtained in the step 2), and continuing to react to obtain the silver nanowires.

The invention innovatively finds that by adopting the composite hydrogel containing the linear polymer and the branched polymer as a terminal blocking material (terminal blocking agent), the silver nanowire with high length, high length-diameter ratio, high purity (less silver nanoparticles) and ultrathin terminal blocking layer can be obtained unexpectedly, and not only the photoelectric property and the carrier transmission property of the prepared silver nanowire can be improved.

The invention discovers for the first time that the length and the length-diameter ratio of nano silver can be unexpectedly improved by adopting the hydrogel as the end-capping reagent prepared from the silver nanowires, particularly the composite hydrogel formed by the linear and branched chain compounded NVP polymer, the thickness of the end-capping layer is reduced, and the photoelectric property and the carrier transmission property are improved; moreover, the side yield of the nano particles can be reduced, and the purity of the silver nano wires can be improved.

In the invention, the linear and branched mixed composite hydrogel as a blocking agent is the key for improving the length-diameter ratio, reducing the blocking thickness and improving the purity and performance. The capping layer first layer molecules are chemically bonded to the Ag surface through Ag-O bonds, while the outer layer is physically adsorbed on the first layer through van der waals interactions. The branched end capping agent inevitably generates strong steric hindrance between outer layers in the process of multilayer adsorption, so that the branched end capping agent is difficult to accumulate and is easy to desorb. The existence of water changes the seed formation of Ag NWs and the growth process of nanowires from the aspect of dynamics, and reduces the generation of AgNPs byproducts.

In the invention, the composite hydrogel can be realized based on the preferable scheme A and scheme B:

scheme A: in the step (1), the composite hydrogel is obtained by mixing and hydrating a linear polymer and a branched polymer. In scheme a, the linear and branched polymers are directly available ex-situ from existing commercial NVP polymerization polymers.

In the embodiment a, the number average molecular weight and the ratio of the linear polymer and the branched polymer can be adjusted according to the actual use requirement. Preferably, the number average molecular weight of the linear polymer is 2 to 100 ten thousand. Preferably, the number average molecular weight of the branched polymer is 2 to 100 ten thousand. The mass ratio of the linear polymer to the branched polymer is 100000-1: 1 to 100000.

Another embodiment of the present invention for obtaining the composite hydrogel (embodiment B): the aqueous solution containing NVP monomer and initiator is obtained by initiating reaction. The preferred embodiment B, based on the NVP and the initiator, polymerizes and gels in one step to obtain linear and branched composite hydrogels.

The initiator is preferably an initiator that polymerizes the NVP to form linear and branched polymers. The amount of initiator used is not less than the minimum theoretical amount to initiate NVP polymerization.

Preferably, the initiator is g-C₃N₄. The research shows that the effect of the prepared composite hydrogel on improving the aspect ratio and length of the silver nanowire and reducing the thickness of the blocking film can be further improved unexpectedly by adopting the preferred material for initiation.

In the present invention, said g-C₃N₄Can be based onThe preparation method adopts the existing means. Preferably, the initiator g-C₃N₄The preparation process comprises the following steps: in the air atmosphere, heat treatment (sintering) is carried out on melamine at the temperature of 500-600 ℃ to obtain C₃N₄Block, and mixing the C₃N₄The blocks are peeled off under ultrasound.

In scheme B of the present invention, a further preferred preparation process of the composite hydrogel comprises: c is to be₃N₄Stripping the block under ultrasonic wave, and centrifuging to obtain the dispersed g-C₃N₄To g-C₃N₄Adding NVP into the supernatant, and carrying out initiation reaction to obtain the composite hydrogel.

Preferably, g-C₃N₄In the supernatant, g-C₃N₄The concentration is 0.01-1 mg/L. The amount of initiator used may be adjusted to ensure that the reaction is induced, based on the preparation requirements, e.g. g-C₃N₄The volume ratio of the supernatant to NVP is 1:2-1: 6.

In the present embodiment B, the reaction initiating condition is preferably uv irradiation.

Preferably, the wavelength of ultraviolet is 250-380 nm; the time of ultraviolet initiation reaction is 1-10 h.

The invention innovatively utilizes the composite hydrogel as a capping agent, silver nano seed crystals are formed under the assistance of the capping agent, and the silver nano wires are prepared through further reaction.

Preferably, in step 2), the control agent is a metal halide, preferably CuCl₂、FeCl₃、NaCl、NaBr、CuBr₂At least one of (1).

In the invention, the polyalcohol is at least one of glycol, pentanediol, glycerol and butanediol.

In the present invention, the base solution may be obtained by dissolving the composite hydrogel in a polyol in advance and then mixing the resulting solution with a polyol solution in which a control agent is dissolved.

In the invention, the silver source solution A can be added into the base solution and then heated for pre-reaction, or the base solution is heated to the pre-reaction temperature in advance, and then the silver source solution A is added for pre-reaction to obtain the crystal seed solution.

Preferably, the silver source in the silver source solution A is a water-soluble silver source, preferably AgNO₃、AgClO₄And AgF.

Preferably, the molar concentration of the silver source in the silver source solution A is 0.005-0.02M.

Preferably, the silver source introduced into the silver source solution A accounts for 0.005-5% of the total weight of the silver source; more preferably 0.01 to 1%.

Preferably, in the step 2), the molar ratio of the control agent to the silver source in the silver source solution A is 1:1-1:3 (the silver amount in the step (2).

Preferably, in the step 2), the temperature of the pre-reaction process is 150-; further preferably 160-180 ℃. The research finds that the control of the temperature in the preferable range is beneficial to further facilitating the preparation of the silver nanowire after the high-length-diameter-ratio ultrathin end-sealing layer.

In the invention, after the pre-reaction forms the seed crystal, the silver source solution B is further dripped, and the rest planned amount of silver source is added, thereby obtaining the material.

Preferably, the mol weight of the composite hydrogel is calculated by NVP (N-vinyl pyrrolidone) monomers, and the mol ratio of the composite hydrogel to the total silver source is 2-12: 1; more preferably 7-10: 1. Researches show that under the composite hydrogel, the Ag nanowire with ultrahigh length-diameter ratio and thinner coating layer in the further field is facilitated by further matching with the control of the ratio of NVP/Ag, and the purity of the nanowire is improved.

Preferably, in step 3), the silver source solution B is a silver source polyol solution; the silver source is the same as the silver source solution A, and the selected type of the polyhydric alcohol is the same as the base solution and the silver source solution A. Preferably, the molar concentration of the silver source solution B is 0.05-0.2 mol/L.

Preferably, in the step 3), the adding speed of the silver source solution B is 0.1-1 mL/min; preferably 0.5 to 1 mL/min. It was found that control at this preferred input rate facilitates further preparation of the ultra high aspect ratio, thinner clad Ag nanowires, and in addition, improves nanowire purity.

Preferably, the reaction temperature of the step 3) is controlled at 150-200 ℃; further preferably 160-180 ℃. Researches show that the Ag nanowire with ultrahigh length-diameter ratio and thinner coating layer can be prepared by matching the composite hydrogel, the NVP/Ag dosage and the Ag conveying speed control and further matching the reaction temperature control, and in addition, the purity of the nanowire can be improved.

The invention also provides a more preferable preparation method of the silver nanowires, which comprises the following steps:

1) preparing the block C by thermal polymerization under air atmosphere₃N₄Dispersing in deionized water (preferably polymerization conditions, obtained by directly performing high temperature thermal polymerization on melamine at 550 deg.C for 4h, at 2 deg.C/min), performing ultrasonic treatment, centrifuging at high speed, and collecting supernatant to obtain g-C₃N₄An aqueous solution; g to C₃N₄Mixing the aqueous solution with NVP (preferably at a volume ratio of 1:2-1:6) under stirring, and vertically irradiating under ultraviolet lamp (preferably under curing conditions: ultraviolet light with wavelength of 360nm for 1-12h) to form transparent high viscosity hydrogel (CN/NVP)

2) Adding the required amount of CN/NVP hydrogel (based on NVP, the hydrogel is preferably added in an amount which is equal to the amount of AgNO added subsequently₃The total molar ratio of 2-12: 1) dissolving in EG solution, magnetically stirring in an oil bath, heating to 150-;

3) at room temperature, adding CuCl₂Dissolving in EG, stirring well, and preparing CuCl with required concentration₂Solution (preferably with concentration of 0.005-0.02 mol/L); mixing AgNO₃Dissolving in EG, stirring uniformly, and preparing AgNO with required concentration₃A solution;

4) adding the CuCl of the step 3) into the mixed solution of the step 2)₂The solution is added with AgNO prepared in the step 3) after continuously keeping the constant temperature₃Solution (preferred concentration is 0.005-0.02mol/L, AgNO)₃With CuCl₂Molar ratio of 2:1), kept constantAnd (4) warming.

5) The AgNO obtained in the step 3)₃Injecting the solution (preferably with a concentration of 0.05-0.2mol/L) into the mixed solution (preferably at a rate of 0.5-1mL/min) in the step 4) by a syringe pump, and keeping the mixed solution at a constant temperature (preferably at a temperature of 160-.

In the method, by a polyol method, the linear and branched composite hydrogel formed by self-made NVP polymerization is used for replacing commercial PVP as a blocking agent, the prepared silver nanowire has higher length-diameter ratio, an ultrathin blocking layer and few byproducts, the synthetic process is simple and quick, subsequent complex purification and post-treatment are not needed, and the method is favorable for industrial production. The transparent conductive film prepared based on the silver nanowires has good photoelectric characteristics and carrier transmission performance.

The invention also provides the silver nanowire prepared by the preparation method; the silver nanowire-based composite material comprises silver nanowires and a capping layer coated on the surface of the silver nanowires in situ, wherein the capping layer comprises NVP polymerized linear polymer and branched polymer.

Preferably, the length-diameter ratio of the silver nanowires is more than 1000; the length is 50-200 μm; the thickness of the end capping layer is not higher than 3 nm.

The invention also provides a transparent conductive film comprising the silver nanowire.

Preferably, said use is characterized by the production of electronic and/or optoelectronic devices;

preferably for the production of flexible electronic and/or optoelectronic devices.

Compared with the prior art, the invention has the following effects:

1. the linear and branched composite hydrogel is adopted as the end sealing agent, and compared with a commercial PVP K30 (linear) end sealing agent, the dynamic parameters of Ag atom deposition can be regulated and controlled in the preparation process of the silver nanowire, so that the production of the silver nanowire can be facilitated, the formation of by-product silver particles is reduced, and the silver nanowire with high length-diameter ratio and high purity is obtained.

2. The silver nanowires produced by the method are influenced by intermolecular forces of the composite hydrogel such as CN/NVP branched chains, the surfaces of the silver nanowires are provided with ultrathin end sealing layers, and meanwhile, the silver nanowires are few in silver particles, can be directly applied to preparation of transparent conductive films, do not need complex secondary cleaning and purification treatment, are beneficial to reduction of production cost and improvement of yield, and are beneficial to industrial production.

3. The research of the invention also finds that on the premise of using the innovative linear chain/branched chain composite hydrogel, the molar ratio of the hydrogel to Ag, the temperature of hydrothermal reaction and the conveying speed of Ag in the preparation process are further matched, so that the method is favorable for being unexpectedly cooperated with the composite hydrogel to further improve the purity of the silver nanowire, and not only can the length-diameter ratio of the prepared nanowire be further improved to obtain the ultra-long nanowire, but also the thickness of the end sealing layer can be reduced, so that the end sealing layer with the thickness of single-digit nanometer can be obtained.

Researches show that the AgNW transparent conductive film prepared by the preparation method has high light transmittance, good conductivity and good application prospect.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.

FIG. 1: example 1 optical photographs, SEM images and nmr spectra of CN/NVP hydrogels were prepared under the conditions of example 1.

FIG. 2: SEM images of Ag NWs prepared under the conditions of example 1 and their length and diameter histograms.

FIG. 3: example 1 preparation of silver nanowires without treatment of CN/NVP gel (CN/NVP-wrapped Ag NW) and by-product comparison with commercial PVP-wrapped Ag NW (PVP-wrapped Ag NW, comparative example 1): among them, SEM images (a, c) and dark field optical images (b, d) of CN/NVP-wrapped (a, b) and PVP-wrapped Ag NWs (c, d), and high magnification SEM images of inset a, c: CN/NVP-wrapped and PVP-wrapped Ag NWs.

FIG. 4: example 1 the thickness of the capping layer on the untreated CN/NVP-wrappedAg NW surface was compared to PVP-wrappedAgNW: among these, negative-stained SEM images (a, c) and HRTEM images (b, d) of PVP-wrapped (a, b) and CN/NVP-wrapped Ag NW (c, d).

FIG. 5: out-of-plane electron transport properties of single carrier devices: wherein, (a) a schematic diagram of a single carrier device structure; (b) I-V curve of silver nanowire thin film single carrier device with same transmittance.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Example 1

According to the following method, the high-length-diameter ratio, high-purity and ultrathin capping layer silver nanowire is prepared and applied to the preparation of the transparent conductive film.

1) Heat treating melamine at 550 deg.C for 4h, wherein the heating rate is 2 deg.C/min to obtain block C₃N₄Powder; block shape C₃N₄Placing 0.005g of the powder in 100mL of deionized water, and performing ultrasonic treatment to obtain ultrathin nanosheet (g-C)₃N₄) Centrifuging at 10000rpm to obtain the product containing the stripped g-C₃N₄The supernatant of (a);

2) g-C prepared as above₃N₄Mixing the nanosheet solution with NVP (volume ratio of 1:4), stirring, and vertically irradiating for 4h under a 360nm 12W ultraviolet lamp to form the fully transparent high-viscosity hydrogel.

3) A250 mL round bottom flask was charged with 1.0g CN/NVP hydrogel (10: 1 molar ratio converted to NVP to total Ag) and 20mL EG solution, magnetically stirred in an oil bath and warmed to 160 ℃ and held constant temperature for 1 h. Subsequently, 35. mu.L of 0.01mol/L CuCl was added to the mixed solution₂The temperature of the solution is kept constant for 30min, and then 70 mu L of 0.01mol/LAgNO is added₃Adding EG solution into the mixed solution, and maintaining the constant temperature for 35min to promoteForming five-layer twin crystal Ag nano seeds;

4) 7mL of 0.1mol/LAgNO was injected into the round bottom flask by a two-channel syringe pump at a rate of 0.5mL/min₃An EG solution. The reaction was continued at 160 ℃ for about 30 minutes, and then the silver nanowire mixture was naturally cooled to room temperature. The obtained CN/NVP-coated silver nanowire (CN/NVP-wrappedAg NW) is collected after being centrifuged at 2000rpm for 10min and then is dispersed in ethanol for standby.

5) 200. mu.L of 1.0mg/mL Ag NW ethanol dispersion was applied to 2X 2cm PET substrate pieces 2 times by spin coating and dried naturally.

The preparation yielded Ag NWs of relatively uniform diameter and aspect ratio exceeding 1200, with average length up to 78 μm, average diameter 63nm, ultra-thin capping layer thickness of 1nm, and negligible co-generated byproduct AgNPs.

Example 2

1) A250 mL round bottom flask was charged with 0.7g of CN/NVP hydrogel (same as in example 1; molar ratio converted to NVP to total Ag 7:1) and 20mL of EG solution, magnetically stirred in an oil bath and warmed to 160 ℃ and held constant for 1 h. Subsequently, 35. mu.L of 0.01mol/L CuCl was added to the mixed solution₂The temperature of the solution is kept constant for 30min, and then 70 mu L of 0.01mol/LAgNO is added₃Adding the EG solution into the mixed solution, and keeping the temperature constant for 35min to promote the formation of quintuple twin Ag nano seeds;

2) 7mL of 0.1mol/LAgNO was injected into the round bottom flask by a two-channel syringe pump at a rate of 0.5mL/min₃An EG solution. The reaction was continued at 160 ℃ for about 30 minutes, and then the silver nanowire mixture was naturally cooled to room temperature. The obtained silver nanowire coated with CN/NVP is collected after being centrifuged at 2000rpm for 10min and then is dispersed in ethanol for standby.

The addition of the CN/NVP gel from 1.0g to 0.7g in example 1 produced Ag NWs with an aspect ratio of 740, average length of 65 μm and average diameter of 88nm, with a small amount of co-produced AgNPs as a by-product.

Comparative example 1

Compared to example 1, the hydrogel initiated in example 1 was replaced with conventional linear PVP, specifically:

1) a250 mL round bottom flask was charged with 0.1667g PVP K30 (Shanghai nationality, guaranteed GR, 99%, straight chain) and 20mL EG solution, magnetically stirred in an oil bath and warmed to 160 ℃ and held constant temperature for 1 h. Subsequently, 35. mu.L of 0.01mol/L CuCl was added to the mixed solution₂The temperature of the solution is kept constant for 30min, and then 70 mu L of 0.01mol/LAgNO is added₃Adding EG solution into the mixed solution, and keeping the constant temperature for 35 min;

2) 5mL of 0.1mol/LAgNO was injected into the round bottom flask by a two-channel syringe pump at a rate of 0.5mL/min₃An EG solution. The reaction was continued at 160 ℃ for about 30 minutes, and then the silver nanowire mixture was naturally cooled to room temperature. The obtained PVP-coated silver nanowire (PVP-wrappedAg NW) is collected after being centrifuged for 10min at 2000rpm and then is dispersed in ethanol for standby.

3) 200 μ L of 0.8mg/mL Ag NW ethanol dispersion was applied to 2X 2cm PET substrate pieces by spin coating, followed by drying.

The CN/NVP hydrogel from example 1 was replaced with commercial PVP K30, the most suitable experimental parameters of PVPK30 were adjusted to produce Ag NWs with aspect ratio of 350, average length up to 25 μm, average diameter of 70nm, capping layer thickness of 4nm, and substantial co-production of Ag NPs as a by-product.

Comparative example 2

Compared with the example 1, the method adopts the low-concentration CN/NVP hydrogel as the end-capping agent, and specifically comprises the following steps:

1) a250 mL round bottom flask was charged with 0.1g of CN/NVP hydrogel (same as in example 1; 1:1) in terms of mol ratio of NVP to total Ag and 20mL of EG solution, magnetically stirring in an oil bath, raising the temperature to 160 ℃ and keeping the temperature constant for 1 h. Subsequently, 35. mu.L of 0.01mol/L CuCl was added to the mixed solution₂The temperature of the solution is kept constant for 30min, and then 70 mu L of 0.01mol/LAgNO is added₃Adding the EG solution into the mixed solution, and keeping the temperature constant for 35min to promote the formation of quintuple twin Ag nano seeds;

2) 7mL of 0.1mol/LAgNO was injected into the round bottom flask by a two-channel syringe pump at a rate of 0.5mL/min₃An EG solution. The reaction was continued at 160 ℃ for about 30 minutes, howeverAnd naturally cooling the silver nanowire mixed solution to room temperature. The obtained silver nanowire coated with CN/NVP is collected after being centrifuged at 2000rpm for 10min and then is dispersed in ethanol for standby.

The CN/NVP gel loading in example 1 was varied from 1.0g to 0.2g, and the synthesis conditions were fully referenced to commercial PVPK30 to produce AgNWs with an average length of 160 μm and an average diameter of 111nm with a small amount of co-produced by-product Ag NPs.

Comparative example 3

Compared with the example 1, the method for preparing the nano-crystalline silicon dioxide/NVP hydrogel comprises the following steps:

1) a250 mL round bottom flask was charged with 1.5g of CN/NVP hydrogel (same as in example 1; calculated as a molar ratio of NVP to total Ag of 15:1) and 20mL of EG solution, magnetically stirred in an oil bath and warmed to 160 ℃ and held constant for 1 h. Subsequently, 35. mu.L of 0.01mol/L CuCl was added to the mixed solution₂The temperature of the solution is kept constant for 30min, and then 70 mu L of 0.01mol/LAgNO is added₃Adding the EG solution into the mixed solution, and keeping the temperature constant for 35min to promote the formation of quintuple twin Ag nano seeds;

The addition of the CN/NVP gel in example 1 was changed from 1.0g to 1.5g to produce Ag NWs with an aspect ratio 422, average length of 36 μm and average diameter of 85nm, resulting in a large amount of Ag NPs, even forming a one-dimensional AgNPs chain structure.

Comparative example 4

Compared with the embodiment 1, the method has the advantages that in the growth process of the nanowire, the adding speed of the silver source B is increased, and the method specifically comprises the following steps:

1) a250 mL round bottom flask was charged with 1.0g CN/NVP hydrogel and 20mL EG solution, magnetically stirred in an oil bath and warmed to 160 ℃ and held at constant temperature for 1 h. Subsequently, 35. mu.L of 0.01mol/L CuCl was added to the mixed solution₂EG solution, continue to protectKeeping the temperature constant for 30min, and then keeping 70 mu L of 0.01mol/L AgNO₃Adding the EG solution into the mixed solution, and keeping the temperature constant for 35min to promote the formation of quintuple twin Ag nano seeds;

2) 7mL of 0.1mol/LAgNO was injected into the round bottom flask by a two-channel syringe pump at a rate of 2.0mL/min₃An EG solution. The reaction was continued at 150 ℃ for about 30 minutes, and then the silver nanowire mixture was naturally cooled to room temperature. The obtained silver nanowire coated with CN/NVP is collected after being centrifuged at 2000rpm for 10min and then is dispersed in ethanol for standby.

The syringe pump speed in example 1 was adjusted from 0.5mL/min to 2.0mL/min, producing a small amount of Ag NWs with a large amount of co-produced byproduct AgNPs.

Comparative example 5

Compared with the example 1, the growth temperature is reduced, specifically:

1) a250 mL round bottom flask was charged with 1.0g CN/NVP hydrogel and 20mL EG solution, magnetically stirred in an oil bath and warmed to 140 ℃ and held at constant temperature for 1 h. Subsequently, 35. mu.L of 0.01mol/L CuCl was added to the mixed solution₂Keeping constant temperature for 30min in EG solution, and then adding 70 mu L of 0.01mol/L AgNO₃Adding the EG solution into the mixed solution, and keeping the temperature constant for 35min to promote the formation of quintuple twin Ag nano seeds;

2) 7mL of 0.1mol/LAgNO was injected into the round bottom flask by a two-channel syringe pump at a rate of 0.5mL/min₃An EG solution. The reaction was continued at 140 ℃ for about 30 minutes, and then the silver nanowire mixture was naturally cooled to room temperature. The obtained silver nanowire coated with CN/NVP is collected after being centrifuged at 2000rpm for 10min and then is dispersed in ethanol for standby.

The heating temperature in example 1 was adjusted from 160 ℃ to 140 ℃ with a large amount of Ag particles.

Comparative example 6

Compared with the example 1, the hydrogel initiated in the example 1 is replaced by the commercial PVPK30 hydrogel gelled under the irradiation of hydrogen peroxide ultraviolet light, and the specific steps are as follows:

1) a250 mL round bottom flask was charged with 1g PVP K30 hydrogel (2: 8 water to PVP by weight) and 20mL EG solution in an oil bath magnetStirring and heating to 160 ℃ and keeping the constant temperature for 1 h. Subsequently, 35. mu.L of 0.01mol/L CuCl was added to the mixed solution₂The temperature of the solution is kept constant for 30min, and then 70 mu L of 0.01mol/LAgNO is added₃Adding EG solution into the mixed solution, and keeping the constant temperature for 35 min;

2) 7mL of 0.1mol/LAgNO was injected into the round bottom flask by a two-channel syringe pump at a rate of 0.5mL/min₃An EG solution. The reaction was continued at 160 ℃ for about 30 minutes, and then the silver nanowire mixture was naturally cooled to room temperature.

In comparison to example 1, there were only a small number of nanowires in the finished product prepared from the commercial PVP K30 hydrogel, whereas a large number of AgNPs were present.

As can be seen from SEM in FIG. 1, the CN/NVP hydrogel forms a three-dimensional porous cross-linked network structure after drying, unlike PVP and NVP¹³C NMR spectra, the CN/NVP hydrogel, showed two new peaks at 70ppm and 56ppm shifts, corresponding to the 4C atom and the hypomethylene C atom of the pyrrolidone ring, respectively, which further confirms the formation of N-C-O crosslinks or N-C-O-C-N crosslinks as shown in FIG. 1(C), indicating the conversion of a portion of the pyrrolidone rings to succinimide rings and the formation of branches in the CN/NVP hydrogel.

As can be seen from the SEM image of fig. 2, the CN/NVP-wrappedagnws had a relatively uniform diameter and an aspect ratio of over 1200, the average length of the Ag NWs reached 78 μm, the average diameter was 63nm, and the symbiotic by-product AgNPs were negligible.

As can be seen from the SEM images and dark field optical photographs of the unpurified CN/NVP-wrated synthesized in example 1 and the synthesized PVP-wrappAgNWs in comparative example 1 in FIG. 3, the PVP-wrappedAg NWs contained a large amount of random Ag NPs, while the CN/NVP-wrappedAg NWs contained only a small amount of particles and was almost negligible.

From the SEM control results of fig. 4, it is clear that thicker PVP coating was evident on the PVP-wrappedAg NW surface (fig. 4 a); while there was no significant organic layer coating on the surface of the CN/NVP-wrappedAg NW (FIG. 4 c). Meanwhile, from the TEM control results of fig. 4b and 4d, in the PVP-wrappedAg NW, more than 4nm amorphous regions were present in the region next to the silver crystalline structure; whereas CN/NVP-wrappAg NW, the amorphous region is only around 1nm and the bilayer PVP (-0.7 nm) is predicted near the theoretical limit.

Utilizing commercial polyvinylpyrrolidone (PVP-wrappedAg NW), CN/NVP hydrogel silver nanowire (CN/NVP-wrappedAg NW) transparent conductive films with the same transmittance (85%) and through NaBH₄The cleaned CN/NVP hydrogel silver nanowire (surface-clean NW) transparent conductive films were used to prepare single carrier devices, and the equivalent circuit of the device is shown in fig. 5 a. FIG. 5b is a J-V curve of Ag NW films to construct a single carrier device. Compared with a PVP-wrappedAgNW thin film device with the same optical performance, the CN/NVP-wrappedAg NW thin film device has the current density 7.7 times higher. The CN/NVP-wrapAgNW thin film device is reduced in the contact resistance of 774 omega/cm compared with the Ag NWs thin film/C60 of the PVP-wrappAgNW thin film device through equivalent circuit calculation²The conductive resistance of the conductive film is reduced by 1908 omega/cm²And the total resistance value of the device is reduced by 2682 omega/cm²It is shown that the capping layer thickness and aspect ratio (areal density) together affect the in-plane and out-of-plane carrier transport of the device, while the CN/NVP-wrapped Ag NW thin film devices with high aspect ratio ultra-thin capping layers have good optoelectronic properties. The single-carrier devices constructed by CN/NVP-wrapped and surface-cleaned NW films with the same transmittance have relatively close current density, and the end capping layer on the AgNWs surface is removed, so that the current density is only improved by 1.2 times. Obviously, the ultrathin end capping layer can effectively reduce the resistance of the AgNWs thin film and Ag NW thin film/active layer interface, and ensures that the CN/NVP-wrappage Ag NW thin film device has the in-plane and out-of-plane carrier transport performance which is comparable to that of a surface-clear dAg NW thin film device.

While particular embodiments of the present invention have been illustrated and described, it would be obvious that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.

Claims

1. A preparation method of silver nanowires is characterized by comprising the following steps:

step 1): obtaining Linear and branched polymers comprising NVP polymerizationThe composite hydrogel of (a); the composite hydrogel is obtained by carrying out initiation reaction on an aqueous solution containing NVP monomer and an initiator; the initiator is g-C₃N₄；

Step 2): dissolving the composite hydrogel and a control agent in polyhydric alcohol to obtain a base solution, then adding a silver source solution A into the base solution, carrying out pre-reaction, and synthesizing a nano-silver seed crystal solution; the control agent is metal halide;

step 3): dripping the silver source solution B into the nano silver seed crystal solution obtained in the step 2), and continuously reacting to obtain silver nanowires;

the mol weight of the composite hydrogel is calculated by NVP (N-vinyl pyrrolidone) monomers, and the mol ratio of the composite hydrogel to the total silver source is 2-12: 1;

the adding speed of the silver source solution B is 0.1-1 mL/min;

the reaction temperature of the step 3) is controlled to be 150-200 ℃.

2. The method for preparing silver nanowires of claim 1, wherein in the step (1), the composite hydrogel is obtained by mixing and hydrogelling a linear polymer and a branched polymer.

3. The method of preparing silver nanowires of claim 1, wherein the linear polymer has a number average molecular weight of 2 to 100 ten thousand.

4. The method of preparing silver nanowires of claim 1, wherein the branched polymer has a number average molecular weight of 2 to 100 ten thousand.

5. The method for preparing silver nanowires according to claim 1, wherein the mass ratio of the linear polymer to the branched polymer is 100000-1: 1 to 100000.

6. The method of preparing silver nanowires of claim 1, wherein the initiator g-C₃N₄The preparation process comprises the following steps:

in the air atmosphere, the melamine is subjected to heat treatment at the temperature of 500-600 ℃ to obtain g-C₃N₄Blocking the block, and mixing the g-C₃N₄The blocks are peeled off under ultrasound.

7. The method for preparing silver nanowires of claim 6, wherein the composite hydrogel is prepared by the following steps: g to C₃N₄Stripping the block under ultrasonic wave, and centrifuging to obtain the dispersed g-C₃N₄To g-C₃N₄Adding NVP into the supernatant, and carrying out initiation reaction to obtain the composite hydrogel.

8. The method of preparing silver nanowires of claim 7, wherein g-C₃N₄In the supernatant, g-C₃N₄The concentration is 0.01-1 mg/L; g-C₃N₄The volume ratio of the supernatant to NVP is 1:2-1: 6.

9. The method for preparing silver nanowires of claim 1, wherein in step 1), the reaction is initiated under ultraviolet irradiation.

10. The method for preparing silver nanowires of claim 1, wherein the wavelength of ultraviolet light is 250 to 380 nm; the time of ultraviolet initiation reaction is 1-10 h.

11. The method of preparing silver nanowires of claim 1, wherein in step 2), the control agent is CuCl₂、FeCl₃、NaCl、NaBr、CuBr₂At least one of (1).

12. The method of claim 1, wherein the silver source solution A, B is AgNO₃、AgClO₄And AgF.

13. The method for preparing silver nanowires of claim 1, wherein in the step 2), the molar ratio of the control agent to the silver source in the silver source solution a is 1:1 to 1: 3.

14. The method for preparing silver nanowires of claim 1, wherein in the step 2), the polyol is at least one of ethylene glycol, pentanediol, glycerol, and butanediol.

15. The method for preparing silver nanowires of claim 1, wherein the temperature during the pre-reaction is 150 to 200 ℃.

16. The method for preparing silver nanowires of claim 1, wherein the temperature of the pre-reaction process is 160-180 ℃.

17. The method for preparing silver nanowires according to claim 1, wherein the solubility of the silver source in the silver source solution a is 0.005 to 0.02 mol/L; the silver source introduced into the silver source solution A accounts for 0.005-5% of the total weight of the silver source.

18. The method for preparing silver nanowires of claim 1, wherein in step 3), the molar concentration of the silver source solution B is 0.05 to 0.2 mol/L.

19. The method for preparing silver nanowires of claim 1, wherein the adding speed of the silver source solution B is 0.5-1 mL/min.

20. The method for preparing silver nanowires of claim 1, wherein the reaction temperature in step 3) is controlled at 160-180 ℃.

21. Silver nanowires produced by the production method according to any one of claims 1 to 20; the silver nanowire/branched polymer composite material is characterized by comprising silver nanowires and a capping layer coated on the surface of the silver nanowires in situ, wherein the capping layer comprises a linear polymer and a branched polymer polymerized by NVP.

22. Silver nanowires produced by the production method according to claim 21; the preparation method is characterized in that the length-diameter ratio of the silver nanowire is more than 1000; the length is 50-200 μm; the thickness of the end capping layer is not higher than 3 nm.

23. A transparent conductive film comprising the silver nanowire according to claim 21 or 22.

24. Use of the transparent conductive film according to claim 23 for the preparation of an electronic and/or optoelectronic device.

25. Use of the transparent conductive film according to claim 24 for the preparation of flexible electronic and/or optoelectronic devices.