Silver nanowires, a method for preparing the same, and a flexible composite film prepared from the silver nanowires and a method for preparing the same

Abstract

The present application relates to the technical field of nanometer material preparation, and particularly relates to silver nanowires, a preparation method thereof, and a flexible composite film prepared from the silver nanowires and a preparation method thereof. The silver nanowires are obtained by mixing a gallic acid solution and a glucose solution, adding a silver precursor solution under acidic conditions, and performing ultrasonic treatment under light irradiation, and then performing centrifugation and washing. The silver nanowires with a single morphology and uniform size are prepared by controlling the proportion of each component, and the operation method is simple, the production process is green and environmentally friendly, and the production cost is low. The water dispersion of the obtained silver nanowires is deposited on a mixed cellulose film, and then the flexible composite film is obtained through drying, fumigation and curing. The composite film prepared from the obtained silver nanowires has excellent conductivity, acid resistance, mechanical flexibility, protein adsorption resistance and antibacterial property.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanomaterial preparation, and particularly relates to silver nanowires, a preparation method thereof, and a flexible composite film prepared from the silver nanowires and a preparation method thereof. BACKGROUND

[0002] Silver nanowires are one-dimensional nanomaterials with a radial size limited to a nanoscale between 1-100 nm. Silver nanowires not only have excellent electrical conductivity and thermal conductivity required by conductive materials, but also have good flexibility, chemical and mechanical stability, and exhibit superior performance in terms of light, electricity, magnetism and antibacterial properties, and are widely used in the technical fields of plasmonic imaging, solar cells, touch screens, electronic circuits and the like.

[0003] At present, the preparation methods of silver nanowires mainly include physical methods, chemical methods and biological synthesis methods. Among them, the physical method includes laser sputtering method, arc method and the like, which vaporizes large-size bulk materials by laser or high temperature, and then condenses on a low-temperature substrate to finally prepare silver nanowires. The physical method has high requirements for equipment and is complex to operate. The chemical method includes polyol method, seed method, template method, wet chemical method, photoreduction method and the like, which reduces silver ions into silver nanoparticles, aggregates into large particles and finally grows into silver nanowires. The chemical method has simple equipment process, high repeatability and high product yield, but the production cost of this kind of method is high, and at the same time, some organic reagents such as polyvinylpyrrolidone or polyvinyl alcohol are used, which involves the use of some toxic chemicals and causes certain environmental pollution. The biological synthesis method uses some components of plant extracts as reducing agents or stabilizers to reduce silver ions into elemental silver, and finally synthesizes silver nanowires. This method has mild operating conditions, low cost and is green and environmentally friendly, which meets the principle of green development, but the silver nanowires obtained by the green synthesis method will generate a mixture of non-single morphology, and the size of the obtained silver nanowires is not uniform.

[0004] Flexible transparent conductive films are widely used in the fields of organic light-emitting diodes, liquid crystal displays, touch panels, solar cells, wearable sensors, medical devices and the like due to their strong flexibility and conductivity. In the application process of thin films in wearable electronic devices and medical devices, the thin films will be contaminated by microorganisms from the environment or human body, which will seriously affect the performance of the thin films, so the thin films are required to have good inhibition effect on common pathogenic bacteria. At present, the mainstream indium tin oxide film has good conductivity, but its application is limited due to high cost, poor flexibility and great harm to the environment. The flexible film made of silver nanowires has the advantages of low surface resistance, good flexibility, strong conductivity, low price and strong antibacterial property compared with other materials, and is expected to become the optimal choice to replace indium tin oxide. The preparation methods of silver nanowire films include Meyer rod method, spin coating method, drop coating method, spray coating method, dip coating method, vacuum filtration method and brush coating method and the like.

[0005] CN110181074A discloses a method for green preparation of high aspect ratio silver nanowires by composite soft template method, which uses organic diacid and polyvinyl alcohol as composite soft template, and gallic acid as reducing agent to reduce silver salt to prepare silver nanowires. The method uses polyvinyl alcohol and organic diacid as composite soft template, and consumes a large amount of organic reagent. The reaction time is 1-3 days, which is not conducive to improving production efficiency.

[0006] CN114515836A discloses a method for synthesizing silver nanowires in aqueous phase at low temperature, which uses vitamin C as reducing agent, glucose as surfactant, and 1-allyl-3-methylimidazole as nucleation control agent. However, the reaction time under low temperature condition is as long as 60 hours, which is time-consuming. CN110560705A discloses a method for hydrothermal synthesis of silver nanowires by using iron ions as control agent, and CN104313687A discloses a preparation process of fine silver nanowires with high aspect ratio. Both of them use glucose as reducing agent, polyvinylpyrrolidone and polyvinyl alcohol as template agent, and halide as inducing agent, which consumes a large amount of chemical reagents, is not conducive to environmental protection, and produces high cost.

[0007] CN110576193A discloses a method for preparing ultra-fine silver nanowires by using citrate as reducing agent, and polyvinylpyrrolidone as template agent. CN115647380A discloses a method for preparing silver nanowires by soft template method, which uses lactose as template agent and tea polyphenol as reducing agent to reduce silver salt to prepare silver nanowires. Both of the two methods use halide as control agent, which consumes a large amount of chemical reagents and requires high reaction conditions, resulting in high energy consumption.

[0008] CN109095782A discloses a preparation method of silver nanowire transparent conductive film based on three-dimensional microstructure, which uses glucose as reducing agent, iron sulfate as inducing agent, and polyvinylpyrrolidone as morphology inducing agent to prepare silver nanowires. The method combines the method of "internal layer embedding and heating curing short silver nanowires" with the method of "outer layer modification of long silver nanowires" to prepare silver nanowire transparent conductive film. The method consumes a large amount of organic reagents and produces high energy consumption in the process of film preparation. CN111069626A discloses a green and environmentally friendly preparation method of silver nanowires and a post-processing method of silver nanowire film, which uses glucose as reducing agent to prepare silver nanowires under high-pressure sealed hydrothermal conditions. The method requires high reaction conditions and is time-consuming. The light transmittance of the processed silver nanowire transparent film is poor.

[0009] CN109727706A discloses a flexible transparent conductive film and a preparation method thereof, and the conductive film needs to be prepared under high pressure conditions, which requires high reaction conditions; CN113501996A discloses a flexible cellulose-based conductive composite film and a preparation method and application thereof, and cellulose film is obtained by microbial fermentation, and then the cellulose film is soaked in a graphene and silver nanowire liquid, and the composite film is obtained through freezing solidification, vacuum drying and hot pressing treatment, and the preparation process is relatively complex; CN110164590A discloses a graphene flexible high-conductive film with a sandwich structure and a preparation method and application thereof, and the conductive film prepared by the method needs high mass density silver nanowires to obtain a film with good conductivity, and the preparation process of the three methods takes a long time.

[0010] Therefore, it is of important research significance to provide a silver nanowire preparation method with simple process and high repeatability, and to use the silver nanowires prepared by the method to prepare a flexible composite film, so that the prepared flexible composite film has excellent conductivity and flexibility, and strong acid resistance. SUMMARY

[0011] The present application aims to provide a silver nanowire and a preparation method thereof, and a flexible composite film prepared by the silver nanowire and a preparation method thereof, to solve the problems in the prior art.

[0012] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0013] The present application provides a preparation method of silver nanowires, comprising the following preparation steps:

[0014] (1) mixing a gallic acid solution and a glucose solution, and then adjusting the pH to obtain a first mixed solution;

[0015] (2) adding a silver precursor-containing solution to the obtained first mixed solution to obtain a second mixed solution;

[0016] (3) performing ultrasonic treatment on the second mixed solution obtained in step (2) after sunlight irradiation, and then performing centrifugation and washing to obtain silver nanowires.

[0017] Preferably, the concentration of the gallic acid solution in step (1) is 1-20 g / L;

[0018] The concentration of the glucose solution in step (1) is 5-50 g / L;

[0019] The volume ratio of the gallic acid solution to the glucose solution in step (1) is 1:1-10;

[0020] The step (1) uses sodium hydroxide or potassium hydroxide solution to adjust the pH of the mixed solution; the concentration of the sodium hydroxide solution is 38-42 g / L; the concentration of the potassium hydroxide solution is 54-58 g / L; and the pH of the first mixed solution is 1-7.

[0021] Preferably, the concentration of the silver-containing precursor solution in the step (2) is 0.5-5 g / L.

[0022] The silver-containing precursor solution in the step (2) comprises a silver nitrate solution or a silver acetate solution.

[0023] The volume ratio of the silver-containing precursor solution to the first mixed solution in the step (2) is 1:1-10.

[0024] The mixing temperature in the step (2) is 25-30℃, and the time is 5-24 h.

[0025] Preferably, the time of sunlight irradiation in the step (3) is 1-5 min, and the UVA intensity is 3000-5000 μW / cm 2 .

[0026] The ultrasonic treatment time in the step (3) is 5-25 min, and the ultrasonic power is 100-200 W.

[0027] The centrifugation rate in the step (3) is 5000-15000 rpm, and the centrifugation time is 5-25 min.

[0028] The application also provides silver nanowires prepared by the above method.

[0029] The application also provides a preparation method of a flexible composite film, comprising the following steps:

[0030] (1) dissolving the silver nanowires obtained by the above method in water to obtain a silver nanowire aqueous dispersion;

[0031] (2) depositing the silver nanowire aqueous dispersion on a mixed cellulose membrane, drying, fixing on a substrate, fumigating with acetone vapor, and then curing at room temperature to obtain a flexible composite film.

[0032] Preferably, the concentration of the silver nanowire aqueous dispersion in the step (1) is 5-25 mg / L.

[0033] Preferably, the pore size of the mixed cellulose membrane in the step (2) is 0.1-0.3 μm.

[0034] The deposition density of the silver nanowire aqueous dispersion on the mixed cellulose membrane in the step (2) is 0.01-0.5 mg / cm 2 .

[0035] Preferably, the substrate in the step (2) comprises a polyethylene terephthalate substrate or a polyimide substrate.

[0036] The fumigation time in the step (2) is 0.5-2 min; and the curing time is 3-8 min.

[0037] The application further provides a flexible composite film prepared by the preparation method of the flexible composite film.

[0038] Compared with the prior art, the technical scheme of the application has the following beneficial effects:

[0039] (1) The application uses gallic acid as a reducing agent and glucose as a stabilizer / capping agent, both of which are natural organic raw materials, are widely available, have low cost and no toxic side effects, and the reaction process uses water as a solvent without the need to add additional alcoholic organic reagents, and does not rely on high molecular compounds such as polyvinylpyrrolidone and polyvinyl alcohol as a template agent, which is more environmentally friendly than traditional methods, greatly reducing the production cost of silver nanowires and the wastewater treatment cost.

[0040] (2) The application can prepare silver nanowires with single morphology and uniform size by controlling the ratio of the components; the preparation process is carried out at normal temperature and pressure, the reaction conditions are mild, and silver nanowires can be prepared in only one step, so that the overall process flow is simple, the operation is simple, the repeatability is high, and the application is suitable for existing production systems and is suitable for industrialized large-scale production and application.

[0041] (3) The flexible composite film prepared from the silver nanowires obtained by the application has a sheet resistance of 1-10 Ω / sq, the sheet resistance hardly changes after several bending, the sheet resistance change rate is 5.8% after strong acid treatment, has excellent conductivity and flexibility, strong acid resistance, and the mechanical flexibility far exceeds that of ordinary indium tin oxide on the market, and has a broad application prospect in flexible electronic devices and optical electronic devices. The composite film can be patterned to construct silver nanowire patterns with different widths.

[0042] (4) The flexible composite film prepared from the silver nanowires obtained by the application has deposition density-dependent antibacterial activity and anti-protein adsorption in biological performance. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 FIG. 1 is a 5-μm transmission electron microscope image of silver nanowires prepared in Example 1 of the application;

[0044] Figure 2 FIG. 2 is a 500-nm transmission electron microscope image of silver nanowires prepared in Example 1 of the application;

[0045] Figure 35 μm TEM image of silver nanowires prepared for Example 2 of the present invention;

[0046] Figure 4 500 nm TEM image of silver nanowires prepared for Example 3 of the present invention;

[0047] Figure 5 Patterned optical image and LED bulb test image of flexible composite film prepared for Example 8 of the present invention. DETAILED DESCRIPTION

[0048] The present invention provides a method for preparing silver nanowires, comprising the following preparation steps:

[0049] (1) mixing a gallic acid solution and a glucose solution and then adjusting the pH to obtain a first mixed solution;

[0050] (2) adding a silver precursor-containing solution to the obtained first mixed solution to obtain a second mixed solution;

[0051] (3) performing ultrasonic treatment on the second mixed solution obtained in step (2) after sunlight irradiation, and then performing centrifugation and washing to obtain silver nanowires.

[0052] In the present invention, the concentration of the gallic acid solution in step (1) is 1-20 g / L, preferably 5-15 g / L, further preferably 8-12 g / L, and more preferably 9-11 g / L;

[0053] The concentration of the glucose solution in step (1) is 5-50 g / L, preferably 10-40 g / L, further preferably 15-35 g / L, and more preferably 20-30 g / L;

[0054] The volume ratio of the gallic acid solution to the glucose solution in step (1) is 1:1-10, preferably 1:3-8, and further preferably 1:4-6;

[0055] In step (1), a sodium hydroxide or potassium hydroxide solution is used to adjust the pH of the mixed solution;

[0056] The concentration of the sodium hydroxide solution is 38-42 g / L, preferably 39-41 g / L, and further preferably 40 g / L;

[0057] The concentration of the potassium hydroxide solution is 54-58 g / L, preferably 55-57 g / L, and further preferably 56 g / L;

[0058] The pH of the first mixed solution is 1-7, preferably 4-6, and further preferably 5.

[0059] In the present application, the concentration of the silver-containing precursor solution in step (2) is 0.5-5 g / L, preferably 1-4 g / L, and further preferably 2-3 g / L;

[0060] The silver-containing precursor solution in step (2) comprises a silver nitrate solution or a silver acetate solution, preferably a silver nitrate solution;

[0061] The volume ratio of the silver-containing precursor solution to the first mixed solution in step (2) is 1:1-10, preferably 1:3-8, and further preferably 1:4-6;

[0062] The mixing temperature in step (2) is 25-30℃, preferably 26-29℃, and further preferably 28℃, and the mixing time is 5-24 h, preferably 10-20 h, and further preferably 12-16 h.

[0063] In the present application, the sunlight irradiation time in step (3) is 1-5 min, further preferably 2-4 min, and more further preferably 3 min; the UVA intensity is 3000-5000 μW / cm 2 , preferably 3500-4500 μW / cm 2 , and further preferably 4200 μW / cm 2 ;

[0064] The ultrasonic treatment time in step (3) is 5-25 min, preferably 10-20 min, and further preferably 13-16 min, and the ultrasonic power is 100-200 W, preferably 120-180 W, and further preferably 140-160 W;

[0065] The centrifugation rate in step (3) is 5000-15000 rpm, preferably 8000-13000 rpm, and further preferably 10000-12000 rpm, and the centrifugation time is 5-25 min, preferably 10-20 min.

[0066] The present application also provides silver nanowires prepared by the above method.

[0067] The present application also provides a method for preparing a flexible composite film, comprising the following steps:

[0068] (1) dissolving the silver nanowires obtained by the above method in water to obtain a silver nanowire aqueous dispersion;

[0069] (2) depositing the silver nanowire aqueous dispersion onto a mixed cellulose film, drying, fixing on a substrate, fumigating with acetone vapor, and then curing at room temperature to obtain a flexible composite film.

[0070] In the present application, the concentration of the silver nanowire aqueous dispersion in step (1) is 5-25 mg / L, preferably 10-20 mg / L, and further preferably 12.5-16 mg / L.

[0071] In the present application, the pore size of the mixed cellulose membrane in step (2) is 0.1-0.3 μm, and preferably 0.2 μm.

[0072] The deposition density of the silver nanowire aqueous dispersion on the mixed cellulose membrane in step (2) is 0.01-0.5 mg / cm 2 , preferably 0.05-0.4 mg / cm 2 , further preferably 0.1-0.3 mg / cm 2 , and more preferably 0.2 mg / cm 2 .

[0073] In the present application, the substrate in step (2) comprises a polyethylene terephthalate substrate or a polyimide substrate, and preferably a polyethylene terephthalate substrate.

[0074] The fumigation time in step (2) is 0.5-2 min, and preferably 1-1.5 min; and the curing time is 3-8 min, and preferably 5-7 min.

[0075] The present application also provides a flexible composite film prepared by the above method.

[0076] The technical solutions provided by the present application will be described in detail below in conjunction with the examples, but they should not be understood as limiting the scope of protection of the present application.

[0077] In each embodiment of the present application, the purity of gallic acid, glucose, and silver-containing precursor is all analytical pure.

[0078] Example 1

[0079] (1) 60 mL of a 6 mM aqueous gallic acid solution was added to 90 mL of a 30 mM aqueous glucose solution and mixed uniformly; then a 1 M sodium hydroxide solution was added to adjust the pH to 5, to obtain a first mixed solution;

[0080] (2) The obtained first mixed solution was stirred at 28°C while adding 15 mL of a 5 mM silver nitrate solution, and mixed for 5 h to obtain a second mixed solution;

[0081] (3) The second mixed solution obtained in step (2) was filtered through a 0.2 μm mixed cellulose membrane to obtain a silver nanowire aqueous dispersion; 2After irradiation with a sunlight simulator for 3 minutes, the solution was subjected to ultrasonic treatment for 5 minutes at a power of 100W. The solution was then centrifuged at 10,000 rpm for 15 minutes and washed three times with pure water to obtain silver nanowires.

[0082] pass Figure 1 and Figure 2 As can be seen, the silver nanowires prepared by controlling the proportion of each component in this embodiment have the characteristics of uniform morphology and size.

[0083] Example 2

[0084] (1) Add 60 mL of 12 mM gallic acid aqueous solution to 90 mL of 100 mM glucose aqueous solution and mix well; then add 1 M sodium hydroxide solution to adjust the pH to 4 to obtain the first mixed solution.

[0085] (2) While vigorously stirring the first mixed solution at 28°C, add 15 mL of silver nitrate solution with a molar concentration of 5 mM and mix for 12 h to obtain the second mixed solution.

[0086] (3) The second mixed solution obtained in step (2) was subjected to 4200 μW / cm 2 After irradiation with a sunlight simulator for 3 minutes, the solution was subjected to ultrasonic treatment for 5 minutes at a power of 100W. The solution was then centrifuged at 10,000 rpm for 15 minutes and washed three times with pure water to obtain silver nanowires.

[0087] pass Figure 3 As can be seen, the silver nanowires prepared by controlling the proportion of each component in this embodiment have the characteristics of uniform morphology and size.

[0088] Example 3

[0089] (1) Add 60 mL of 30 mM gallic acid aqueous solution to 90 mL of 200 mM glucose aqueous solution and mix well; then add 1 M sodium hydroxide solution to adjust the pH to 4 to obtain the first mixed solution.

[0090] (2) While vigorously stirring the first mixed solution at 28°C, add 15 mL of silver nitrate solution with a molar concentration of 10 mM and mix for 24 h to obtain the second mixed solution.

[0091] (3) The second mixed solution obtained in step (2) was subjected to 4200 μW / cm 2The silver nanowires were prepared by the method of Example 1, and then were irradiated by the sun simulator for 3 min, and then were ultrasonically treated for 5 min at a power of 100 W. The ultrasonically treated solution was centrifuged at a speed of 10 000 rpm for 15 min, and then was washed with pure water for three times to obtain the silver nanowires.

[0092] By Figure 4 It can be seen that the silver nanowires prepared by controlling the proportion of each component have the characteristics of single morphology and uniform size.

[0093] Test Example 1

[0094] According to the M07-A9 method and M11-A6 method described by the American Clinical Laboratory Standards Institute (Clinical and Laboratory Standards Institute), the antibacterial property of the silver nanowires prepared in Example 1 was tested by the broth dilution method and the plate counting method. Staphylococcus aureus was cultured in soybean broth medium, Escherichia coli was cultured in nutrient broth medium, and Propionibacterium acnes was cultured in an anaerobic environment. The strains reaching the logarithmic growth phase were collected to prepare a bacterial solution (10 8 CFU / mL), the bacterial solution was diluted to 10 6 CFU / mL with the corresponding medium, the bacterial solution and the sample solution were mixed at a ratio of 1:1, Escherichia coli and Staphylococcus aureus were incubated at 37°C for 18 hours, and Propionibacterium acnes was incubated at 37°C for 48 hours in an anaerobic incubator. Then, 100 μL of the liquid without obvious turbidity was taken out and coated with glass beads, and the plate counting was performed after the colonies were clearly visible. The results showed that the silver nanowires had inhibitory effect on various pathogenic bacteria and exhibited good antibacterial effect. The results are shown in Table 1.

[0095] Table 1 Minimum inhibitory concentration and minimum bactericidal concentration of silver nanowires of Example 1 on Escherichia coli, Staphylococcus aureus and Propionibacterium acnes

[0096] Minimum inhibitory concentration (mg / L) Minimum bactericidal concentration (mg / L) Escherichia coli 200 800 Staphylococcus aureus 200 800 Propionibacterium acnes 50 200

[0097] Test Example 2

[0098] The inhibitory effect of the silver nanowires prepared in Example 1 on the formation of bacterial biofilm was studied by crystal violet staining method. The strains reaching the logarithmic growth phase were collected to prepare a bacterial solution (10 8Example 3 100 μL of E. coli, S. aureus, P. acnes were inoculated into 96-well plates (CFU / mL) and 100 μL of silver nanowire solution with concentrations of 12.5, 25, 50 mg / L was added. E. coli, S. aureus were incubated at 37 °C for 24 h, and P. acnes was incubated at 37 °C for 72 h under anaerobic conditions. After that, the culture medium was removed and washed with phosphate buffered saline (PBS) for 3 times. 100 μL of 4 °C pre-cooled methanol solution was added for 15 min and then removed. The sample was air-dried for 20 min, and 100 μL of crystal violet solution (0.5%) was added. After incubation at 30 °C for 20 min, the crystal violet solution was removed, and the sample was washed with PBS for 3 times to remove the excess dye. 160 μL of glacial acetic acid solution (33%) was added to dissolve the bound crystal violet dye, and the absorbance at 590 nm was measured quantitatively. The results showed that silver nanowires exhibited dose-dependent antibiofilm activity, and the biofilm destruction rate increased with the increase of silver nanowire concentration. The results are shown in Table 2:

[0099] Table 2 Inhibition rate of different concentrations of silver nanowires on E. coli, P. acnes, S. aureus biofilm

[0100]

[0101] Example 4

[0102] The silver nanowires prepared in Example 1 were diluted with ultrapure water to 8 mg / L, and then filtered under vacuum with a solvent filter after ultrasonic treatment at 100 W for 30 s to obtain a silver nanowire water dispersion;

[0103] The silver nanowire water dispersion was deposited on a mixed cellulose membrane with a pore size of 0.2 μm, and the deposition density of the silver nanowire water dispersion on the mixed cellulose membrane was 0.01 mg / cm 2 Then the film was placed in a blast drying oven at 50 °C for drying, and then fixed on a polyethylene terephthalate substrate, which was placed on acetone heated to 70 °C, fumigated with acetone vapor for 1 min, and then dried and cured at room temperature for 5 min to completely remove the acetone. The film was peeled off from the polyethylene terephthalate substrate to obtain a flexible composite film.

[0104] Example 5

[0105] The difference from Example 4 is only that the deposition density of the silver nanowire water dispersion on the mixed cellulose membrane is 0.05 mg / cm 2 .

[0106] Example 6

[0107] The difference from Example 4 is only that the deposition density of the silver nanowire water dispersion on the mixed cellulose membrane is 0.1 mg / cm 2 .

[0108] Example 7

[0109] The difference from Example 4 is that the deposition density of the silver nanowire aqueous dispersion on the mixed cellulose film is 0.2 mg / cm 2 .

[0110] Example 8

[0111] The difference from Example 4 is that the deposition density of the silver nanowire aqueous dispersion on the mixed cellulose film is 0.5 mg / cm 2 .

[0112] Comparative Example 1

[0113] The mixed cellulose film was fixed on a polyethylene terephthalate substrate, which was placed on acetone heated to 70°C, fumigated with acetone vapor for 1 min, and dried and cured at room temperature for 5 min to completely remove the acetone. The film was peeled off from the polyethylene terephthalate substrate to obtain a flexible composite film without silver nanowires.

[0114] Test Example 3

[0115] Examples 4-8 of the present application obtained different flexible composite films by controlling different deposition densities. The sheet resistance of the flexible composite films obtained in Examples 5, 6, and 8 was evaluated using a multifunctional digital four-probe measurement instrument (ST2258C), and the flexibility of the films was characterized by measuring the change in square resistance after repeated bending operations on a cylindrical object. The bending film size was 2 cm x 2 cm, and a commercial ITO film was used as a reference control. The results showed that as the deposition density increased, the mechanical properties of the film improved, and after several repeated bendings, the resistance of the composite film hardly changed, showing good mechanical flexibility. The square resistance of the commercial ITO film and the composite films with different deposition densities was tested after 500 repeated bendings, and the results are shown in Table 3:

[0116] Table 3 Square resistance of ITO film and composite films with different deposition densities after 500 repeated bendings

[0117] ITO with different deposition density thin films (mg / cm 2 )]]> ITO 0.05 0.1 0.5 Sheet resistance (Ω / sq) 31.7 3.75 1.75 0.39

[0118] Test Example 4

[0119] The flexible composite film prepared in Example 6 was subjected to heat treatment, acid treatment, and mixed E. coli and S. aureus treatment, and the square resistance change rate of the composite film was tested. The square resistance change rate of the composite film after acid treatment for 1 h was 5.8%, the square resistance change rate after heat treatment was -4.2%, and the square resistance change rate after mixed bacteria treatment was 13.751%, and the results are shown in Table 4:

[0120] Table 4 Square resistance (Ω / sq) after 1 hour of different conditions

[0121] Untreated Acid treated Heat treated Mixed bacteria treated 1.515 1.614 1.448 1.713

[0122] Test Example 5

[0123] like Figure 3 As shown, the flexible composite film prepared in Example 8 was patterned using photolithography and wet chemical etching. The film was cleaned by immersion in isopropanol, rinsed 10 times with ultrapure water to remove isopropanol residue, dried with a nitrogen gun, and then fixed onto a silicon wafer. A positive photoresist polymer was spin-coated onto the film at 500 rpm (5 s) followed by 2000 rpm (30 s). The film was exposed to a contact exposure machine (MA / BA6 Gen4) through a mask and developed for 100 s with a solution of tetramethylammonium hydroxide:H2O = 1:8 (volume ratio). The pre-patterned film was then removed from the exposed areas using a plasma resist remover (M4L). Before wet etching, the film was hardened at 100°C for 2 min, and then immersed in an etchant composed of hydrogen peroxide and ammonium hydroxide for 60 s. The volume ratio of the etching solution was NH4OH:H2O2:H2O = 1:1:10. After chemical etching, the remaining photoresist polymer on the film is removed with anhydrous ethanol solution, and the ethanol is removed by drying at room temperature to obtain a patterned film. Silver nanowire patterns of various shapes and sizes can be constructed and used as transparent flexible circuits. The electrical properties of the silver nanowire patterns can be used to light LED bulbs.

[0124] Test Example 6

[0125] The flexible composite films prepared in Examples 4-8 and Comparative Example 1 were subjected to anti-protein adsorption tests under static conditions to investigate their anti-organic fouling performance. The membrane (1 cm × 1 cm) was immersed in 2 mL of BSA solution at 37 °C for 1 hour, rinsed three times with PBS and ultrapure water, and then transferred to 1 mL of preheated washing solution at 37 °C. The adsorbed BSA protein was eluted by shaking in a shaker for 2 hours. The amount of protein adsorbed by the membrane was calculated using the protein concentration in the washing solution and quantified using a protein detection kit. The results showed that the amount of protein adsorbed on the composite film after silver nanowire deposition decreased, exhibiting a certain degree of deposition density dependence. The anti-organic fouling performance of the membrane was optimized by modifying it with silver nanowire deposition on the mixed cellulose membrane. The results are shown in Table 5.

[0126] Table 5. Adsorption capacity of proteins on flexible composite films with different deposition densities

[0127] Different sediment densities (mg / cm 2 ) 0 0.01 0.05 0.1 0.2 0.5 Protein adsorption (mg / cm 2 )]]> 0.67 0.62 0.61 0.60 0.59 0.58

[0128] Test Example 7

[0129] The antibacterial ability of the flexible composite film prepared in Examples 4-8 and Comparative Example 1 was evaluated by plate counting method. The bacterial strain cultured overnight at 37 DEG C was quantitatively obtained to prepare a bacterial suspension with a concentration of 10 8 CFU / mL, and the bacterial suspension was continuously diluted with sterile culture medium to prepare a working bacterial suspension with a concentration of 10 4 CFU / mL. 1 cm x 1 cm composite film was added to 2 mL bacterial suspension, and the bacterial suspension without the film was used as a control, and then the mixture was cultured at 37 DEG C with shaking. At 6 h, 50 μL of the mixture was diluted and spread on a solid culture medium plate, and the plate was incubated at 37 DEG C until the colonies were clear, and then the colonies were counted. The results showed that the composite film exhibited deposition density-dependent antibacterial activity against E. coli, P. acnes and S. aureus, and the final concentration of the bacteria decreased with the increase of the deposition density, and the strongest inhibition was shown against E. coli. The antibacterial results are shown in Table 6:

[0130] Table 6 Bacterial concentration after 6 h of the silver nanowire composite film with different deposition densities

[0131]

[0132] From the above examples, it can be seen that the present application provides a method for preparing silver nanowires by using gallic acid as a reducing agent and glucose as a stabilizing agent / capping agent. The Ag + reduction kinetics and morphology growth kinetics are analyzed by gravity method and high-speed centrifugation method, and the results show that the reaction starts after the addition of silver nitrate, and the induction growth period starts at 30 min, the crystal nucleus grows into nanoparticles, and the reaction ends at 5 h when the atoms on the surface of the nanoparticles reach equilibrium state with the atoms in the solution. Glucose acts as a stabilizing agent and is adsorbed on the nucleation center of the nanoparticles to form a stacking template for guiding the directional attachment of the nanoparticles and nanorods, and gallic acid mainly plays a slow reduction role, and finally silver nanowires are formed. The method has the characteristics of mild reaction conditions, cheap and readily available raw materials, easy operation, low cost, green environmental protection, etc.

[0133] The present application can prepare silver nanowires with single morphology and uniform size by controlling the ratio of the components, and the preparation process is carried out at normal temperature and pressure, the reaction conditions are mild, and the silver nanowires can be prepared by only one step, so that the overall process flow is simple, the operation is simple, the repeatability is high, and the method is suitable for the existing production system and is suitable for industrialized large-scale production and application. The flexible composite film prepared by using the obtained silver nanowires has excellent conductivity, acid resistance, mechanical flexibility, protein adsorption resistance and antibacterial property.

[0134] The above merely describes the preferred embodiments of the present application, and it should be pointed out that, for those skilled in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A method for preparing silver nanowires, characterized by, The preparation method comprises the following steps: (1) mixing a gallic acid solution and a glucose solution, and then adjusting the pH to obtain a first mixed solution; (2) adding a silver precursor solution into the first mixed solution to obtain a second mixed solution; (3) performing sunlight irradiation on the second mixed solution obtained in step (2), and then performing ultrasonic treatment, centrifugation and washing to obtain silver nanowires; In step (1), the concentration of the gallic acid solution is 1-20 g / L; the concentration of the glucose solution is 5-50 g / L; the volume ratio of the gallic acid solution to the glucose solution is 1:1-10; and the pH of the first mixed solution is 1-7. In step (2), the concentration of the silver precursor solution is 0.5-5 g / L; and the volume ratio of the silver precursor solution to the first mixed solution is 1:1-10. The time of sunlight irradiation in the step (3) is 1-5 min, and the UVA intensity is 3000-5000 μW / cm 2 .

2. The method for preparing silver nanowires according to claim 1, characterized in that, In step (1), the pH of the mixed solution is adjusted by using a sodium hydroxide solution or a potassium hydroxide solution; the concentration of the sodium hydroxide solution is 38-42 g / L; and the concentration of the potassium hydroxide solution is 54-58 g / L. 3.The method of claim 1 or 2, wherein the silver nanowires are prepared by the method of claim 1 or 2. In step (2), the silver precursor solution comprises a silver nitrate solution or a silver acetate solution. In step (2), the mixing temperature is 25-30°C, and the mixing time is 5-24 h. 4.The method of claim 3, wherein the silver nanowires are prepared by the method of claim 1 or 2. In step (3), the ultrasonic treatment time is 5-25 min, and the ultrasonic power is 100-200 W. In step (3), the centrifugation rate is 5000-15000 rpm, and the centrifugation time is 5-25 min.

5. The silver nanowires prepared by the preparation method of the silver nanowires according to any one of claims 1-4.

6. A method of making a flexible composite film, characterized by, The preparation method comprises the following steps: (1) dissolving the silver nanowires according to claim 5 in water to obtain a silver nanowire aqueous dispersion; (2) depositing the silver nanowire aqueous dispersion onto a mixed cellulose membrane, drying, fixing on a substrate, fumigating by using acetone vapor, and then curing at room temperature to obtain a flexible composite film.

7. The method of claim 6, wherein the flexible composite film is prepared by a process comprising: In step (1), the concentration of the silver nanowire aqueous dispersion is 5-25 mg / L.

8. The method of claim 7, wherein the flexible composite film is prepared by a process comprising: In step (2), the pore size of the mixed cellulose membrane is 0.1-0.3 μm. The deposition density of the silver nanowire aqueous dispersion in step (2) on the mixed cellulose film is 0.01 to 0.5 mg / cm 2 .

9. A method of making a flexible composite film according to claim 6, 7 or 8, characterised in that, In step (2), the substrate comprises a polyethylene terephthalate substrate or a polyimide substrate. In step (2), the fumigation time is 0.5-2 min; and the curing time is 3-8 min.

10. The flexible composite film prepared by the preparation method of the flexible composite film according to any one of claims 6-9.

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