US20150321257A1

US20150321257A1 - Method for manufacturing silver nanowires using ionic liquid

Info

Publication number: US20150321257A1
Application number: US14/652,084
Authority: US
Inventors: Kwang Suck Suh; Jong Eun Kim; Tae Young Kim
Original assignee: INSCON TECH Co Ltd; SOLOE TECH Co Ltd
Current assignee: INSCON TECH Co Ltd; SOLOE TECH Co Ltd
Priority date: 2012-12-14
Filing date: 2012-12-14
Publication date: 2015-11-12
Also published as: WO2014092220A1; JP2016507640A; CN104870361A; TW201422536A

Abstract

The present invention relates to a method of preparing silver nanowires having a diameter of less than 100 nm and a length of 10 μm or more, and, more particularly, to a method of uniformly preparing silver nanowires having a high aspect ratio using an ionic liquid as an additive in addition to a silver salt precursor, a reducing solvent and a capping agent in a polyol process. When the technology of the present invention is used, silver nanowires having a diameter of less than 100 nm and a length of 10 μm or more can be uniformly prepared. Further, when a transparent conductive film is formed by applying a silver nanowire-dispersed solution onto a base film, the transparent conductive film has a surface resistivity of 10¹˜10³Ω/□ and a light transmittance of 90% or more to the base film.

Description

TECHNICAL FIELD

The present invention relates to a method of preparing silver nanowires and, more particularly, to a method of uniformly preparing silver nanowires having an aspect ratio of 100 or more (for example, having a diameter of less than 100 nm and a length of 10 μm or more) using a silver salt precursor, a reducing solvent, a capping agent and an ionic liquid.

BACKGROUND ART

Recently, touch screen panels have been used as important components of various types of electric, electronic and communication appliances, such as smart phones, tablet computers, etc.
A transparent electrode film is used as a main component of a touch screen panel. As the transparent electrode film, a film having a surface resistivity of 500Ω/□ and a light transmittance of 90% or more to a base film is used. Currently, indium tin oxide (ITO) is generally used as a transparent electrode material. A transparent electrode film having a surface resistivity of 50˜500Ω/□ and a light transmittance of 90% or more to a base film can be fabricated by forming an ITO thin film on a glass substrate or a transparent polymer film using sputtering.
However, the ITO thin film is problematic in that its production cost is very high and it is easily damaged due to the difference in thermal expansibility or thermal shrinkability between the ITO thin film and a base film. Particularly, since the brittleness of the ITO thin film formed on a polymer film is very high, when this ITO thin film is used as a transparent electrode film of a touch screen panel, there is a problem of the ITO thin film being cracked by mechanical or physical deformation.
Therefore, novel raw materials for transparent electrode films, which can overcome the above problems of ITO, have lately attracted considerable attention. For this purpose, there have been many efforts made to fabricate a transparent electrode film using a novel raw material such as a conducting polymer, a carbon nanotube, graphene or a metal nanowire. Particularly, metal nanowire, such as silver nanowire, has lately been in the spotlight as a transparent electrode material that can be used in place of ITO due to the metal wire having very high electroconductvity and a high aspect ratio.
Silver nanowires, as reported in US 2005/0056118, Science 298, 2176, 2002, Chem. Mater. 14, 4736, 2002, can be prepared by a so-called polyol process. Further, there is disclosed a method of synthesizing silver nanowires having a one-dimensional shape in a solution phase using a silver salt precursor (metal precursor), a reducing solvent such as ethyleneglycol (EG) and a capping agent such as polyvinylpyrrolidone (PVP). Further, there was reported a method of synthesizing silver nanowires using an ionic liquid as a capping agent instead of PVP in the polyol process (Angewandte Chemie, 121, 3864, 2009).
However, in such methods of synthesizing silver nanowires, different shapes of silver nanoparticles as well as silver nanowires are simultaneously prepared, so it is not suitable for using these silver nanoparticles as a transparent electrode material. For instance, granular silver nanostructures are prepared together with silver nanowires. In this case, there are problems in that granular silver nanostructures must be separated from silver nanostructures after the preparation of silver nanostructures, and in that the yield of silver nanowires is low.
Further, Korean Unexamined Patent Application Publication No. 10-2010-0055983 discloses a method of preparing metal nanowires by a polyol reduction reaction in which a metal salt is mixed and reacted with a reducing solvent in the presence of an ionic liquid.
However, in order to fabricate a transparent electrode film having excellent light transmittance and surface resistance characteristics using silver nanowires, it is required to develop a method of more uniformly synthesizing silver nanowires having a higher aspect ratio.

DISCLOSURE

Technical Problem

An object of the present invention is to provide a technology of uniformly and reproducibly preparing silver nanowires having an aspect ratio of 100 or more (for example, having a diameter of less than 100 nm and a length of 10 μm or more) without preparing different shapes of silver nanostructures by a polyol reduction reaction using a metal salt as a precursor.
Other objects of the present invention are not limited to the above-mentioned object, and will be clearly understood from the following descriptions by those skilled in the art.

Technical Solution

The present invention relates to a method of preparing silver nanowires having a high aspect ratio (for example, having a diameter of less than 100 nm and a length of 10 μm or more) using an imidazolium-based ionic liquid as an additive in a polyol process.
In order to accomplish the above object, silver nanowires were prepared by a polyol reaction in which an imidazolium-based ionic liquid (additive) was mixed and reacted with a mixed solution including a silver salt precursor, a reducing solvent and a capping agent.
From the research results of the present inventors, it was found that, in the process of preparing silver nanowires by the polyol reduction reaction of a mixed solution including a silver salt precursor (for example, AgNO₃), a reducing solvent (for example, ethyleneglycol), a capping agent (for example, polyvinylpyrrolidone) and the like, when a small amount of an imidazolium-based ionic liquid was added to the mixed solution as an additive, silver nanowires having a diameter of less than 100 nm and a length of 10 μm or more were uniformly prepared. The silver salt precursor is a compound including a silver cation and an organic or inorganic anion. For example, AgNO₃, AgClO₄, AgBF₄, AgPF₆, CH₃COOAg, AgCF₃SO₃, Ag₂SO₄, CH₃COCH═COCH₃Ag or the like may be used as the silver salt precursor. The silver salt is dissociated in a solvent, and is then converted into metal silver by a reduction reaction.
The reducing solvent is a polar solvent that can dissolve a silver salt. The reducing solvent is referred to as a solvent having two or more hydroxy groups in a molecule thereof, such as diol, polyol or glycol. Specific examples of the reducing solvent may include ethyleneglycol, 1,2-propyleneglycol, 1,3-propyleneglycol, glycerin, glycerol, diethylglycol, and the like. The reducing solvent serves to produce metal silver by inducing the reduction reaction of silver cations at a predetermined temperature or more as well as serves as a solvent for dissolving a silver salt.
The capping agent serves to one-dimensionally grow silver nanoparticles because it is adsorbed (hereinafter, capped) only on a specific crystal plane by the interaction between the capping agent and the silver nanoparticles formed in the initial stage of a synthesis reaction. The capping agent is polyvinylpyrrolidone (PVP) or polyvinylalcohol (PVA).
The imidazolium-based ionic liquid, as represented by Formulas 1 and 2 below, is a monomeric or polymeric compound including an organic cation having an imidazolium group and an organic or inorganic anion. Particularly, in the case where the imidazolium-based ionic liquid including a chlorine ion (Cl⁻) or a bromine ion (Br⁻) as an anion is used as an additive, when a silver salt is converted into metal silver by a polyol reduction reaction, the metal silver nanoparticles are one-dimensionally and uniformly grown by the chemical interaction between the imidazolium-based ionic liquid and a silver ion or metal silver, thus finally forming silver nanowires having a high aspect ratio, that is, having a diameter of less than 100 nm and a length of 10 μm or more.
In the present invention, the aspect ratio of silver nanowires is 100 or more, but the upper limit thereof is not predetermined and can be adjusted to the maximum aspect ratio to such a degree that they can exist as silver nanowires by controlling the content of the ionic liquid. When the aspect ratio of silver nanowires is excessively large, they do not exist in the form of wire, and they may be entangled as yarn. Therefore, if necessary, uniform silver nanowires having a high aspect ratio can be prepared by controlling the content of the ionic liquid.
In the Formulas 1 and 2, R1, R2 and R3 are identical to or different from each other, each of which is hydrogen or a hydrocarbon group of 1 to 16 carbon atoms, and each of which includes at least one heteroatom selected from the group consisting of oxygen, sulfur, nitrogen, phosphorus, fluorine, chlorine, bromine, iodine and silicon. Further, X⁻ is an anion, and is an organic or inorganic compound including a halogen ion such as a chlorine ion (Cl⁻) or a bromine ion (Br⁻). n is a repetitive unit, and is a natural number.
Specific examples of the monomeric cationic compound represented by Formula 1 above may include 1,3-dimethylimidazolium, 1,3-diethylimidazolium, 1-ethyl-3-methylimidazolium (EMIM), 1-butyl-3-methylimidazolium (BMIM), 1-hexyl-3-methylimidazolium (HMIM), 1-octyl-3-methylimidazolium (OMIM), 1-decyl-3-methylimidazolium, 1-dodecyl-3-methylimidazolium and 1-tetradecyl-3-imidazolium, and specific examples of the polymeric cationic compound represented by Formula 2 above may include poly(1-vinyl-3-alkylimidazolium), poly(1-allyl-3-alkylimidazolium) and poly(1-(meth)acryloyloxy-3-alkylimidazolium). In order to synthesize silver nanowires, it is preferred that a chlorine ion (Cl⁻) or a bromine ion (Br⁻) be used as the anion of the ionic liquid of Formula 1 or 2.
Hereinafter, the method of preparing silver nanowires according to the present invention will be described in detail.
First, a silver salt precursor, a reducing agent, a capping agent and an ionic liquid are mixed at an appropriate ratio and then stirred at room temperature for a predetermined amount of time. Subsequently, the mixture is reacted at a temperature of 50˜180° C. for 30 minutes˜7 days to form silver nanowires. When the reaction temperature is low, reaction time is long because it takes more time to grow silver nanowires, but on the other hand, when the reaction temperature is high, silver nanowires are formed relatively rapidly.
In the present invention, in order to uniformly prepare silver nanowires, the content ratio of each of the components of the mixture is important. It is preferred that the capping agent is included in an amount of 1 to 2 mol based on 1 mol of the silver salt precursor, and the ionic liquid is included in an amount of 0.001 to 0.2 mol based on 1 mol of the silver salt precursor. In this case, when the amount of the capping agent is less than 1 mol and the amount of the ionic liquid is less than 0.001 mol, each of which being an excessively low amount, there is a problem in that silver nanowires are not uniformly formed and exist in a mixture of nanowires and nanoparticles. Further, when the amount of the capping agent is more than 2 mol and the amount of the ionic liquid is more than 0.2 mol, each of which being an excessively high amount, there is a problem in that the diameter of silver nanowires increases to 100 nm or more, or three-dimensional silver nanoparticles are formed, and thus it is difficult to form uniform silver nanowires. Particularly, when the ionic liquid is used in an amount of 0.005 to 0.02 mol, it is advantageous to form uniform silver nanowires.
The silver nanowires formed in this way are filtered and then washed with a solvent such as water or alcohol. These filtered silver nanowires are dispersed in a solvent to prepare a silver nanowire-dispersed solution. In this case, it is preferred that water or a water-based solvent be used as the solvent for dispersing the silver nanowires. Specific examples of the solvent for dispersing the silver nanowires may include water, methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol, iso-butanol, hexanol, benzyl alcohol, diacetone alcohol, ethyleneglycol, propyleneglycol, glycerol, 1,4-dioxane, tetrahydrofuran (THF), ethyleneglycol monomethyl ether, ethylenglycol monoethyl ether, ethyleneglycol dimethyl ether, propyleneglycol monomethyl ether, propyleneglycol monoethyl ether, propyleneglycol dimethyl ether, N,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide (DMA), acetonitrile, acetaldehyde, N-methyl-2-pyrrolidone, 2-pyrrolidone, N-vinyl-2-pyrrolidone, dimethylsulfoxide, n-butyrolactone, nitromethane, and ethyl lactate. These solvents may be used independently or in a combination thereof.
The silver nanowire-dispersed solution is prepared by dispersing 0.1˜5 wt % of the silver nanowires of the present invention in 95˜99.9 wt % of the solvent. The silver nanowire-dispersed solution may further include a dispersant and a thickener in order to improve the dispersibility of silver nanowires.
Here, when the content of silver nanowires in the silver nanowire-dispersed solution is less than 0.1 wt %, there are disadvantages in that surface resistivity becomes high because the amount of nanowires is excessively small, and in that coatability becomes poor because wet-coating thickness must be increased. Further, when the content of silver nanowires in the silver nanowire-dispersed solution is more than 5 wt %, there are disadvantages in that it is difficult to coat the silver nanowire-dispersed solution because the amount of nanowires is excessively large, and in that light transmittance becomes low because an excessive amount of silver nanowires is used.
The dispersant serves to allow silver nanowires to be stably dispersed in a solvent by electrostatic repulsion or steric barrier because the dispersant is adsorbed on the surface of silver nanowires. The thickener serves to adjust the fluidity of the silver nanowire-dispersed solution. It is effective that each of the dispersant and the thickener be included in an amount of 0.01 to 10 parts by weight based on 100 parts by weight of the silver nanowire-dispersed solution. Here, when the amount of the dispersant is less than 0.01 wt %, there is a disadvantage in that a dispersion effect is barely exhibited. Further, when the amount thereof is more than 10 wt %, there is a disadvantage in that the amount of the dispersant is excessively large, and thus this dispersant leak out from the surface of the silver nanowire-dispersed solution to decrease the surface resistivity thereof or the surface thereof becomes excessively slippery.
The dispersant may include at least one selected from the group consisting of polyoxyethylene aliphatic ether, polyoxyethylene phenyl ether, polyimine, alkyl phosphate, an alkylammonium salt, a polyester alkylolammonium salt, a polyacrylic alkylolammonium salt, polydimethylsilane, polyacrylic acid, polysulfonic acid and polyvinylpyrrolidone. More specifically, the dispersant may include at least one selected from the group consisting of Triton X-100, Triton X-200, Pluronic P123, F127, F68, L64, BYK-181, 184, 191, 192, 194, Disperbyk-181, 184, 190, Tego 710, 720W, 730W, Zonyl FSN, FSO, FSP, cetyltrimethylammonium bromide (CTAB), cetyltrimethylammonium chloride (CTAC), tetrabutylammonium bromide (TBAB), tetrabutylammonium chloride (TBAC), sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate (SDBS), polystyrene sulfonate (PSSA), poly(sodium-4-styrenesulfonate) (PSSNa), and dodecylbenzenesulfonate (DBSA). Examples of the thickener may include, but are not limited to, a urethane-modified thickener, an acrylic thickener, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose. These thickeners may be used independently or in a combination thereof.
When the silver nanowire-dispersed solution including the silver nanowires prepared by the technology of the present invention is applied onto a base film and then dried, a transparent electrode film including a three-dimensional network formed of silver nanowires having a diameter of less than 100 nm and a length of 10 μm or more can be manufactured.
The base film may be a commonly-used transparent film, but is not limited thereto. For example, the base film may be formed of polyethylene terephthalate, polyester naphthalate, polycarbonate, polymethylmethacrylate, polyacrylate, polyacrylonitrile, polystyrene or the like. Meanwhile, in order to improve the adhesivity between the base film and the silver nanowires, an adhesion enhancing layer may be applied to the surface of the base film or the base film may be surface-treated by corona treatment, plasma treatment or the like.
As the method of coating a base film with silver nanowires, all commonly-known technologies may be used. General examples of the coating method may include, but are not limited to, dip coating, spin coating, bar coating, gravure printing, reverse gravure printing, offset printing, ink-jet printing, spray coating and slot die coating.
The transparent electrode film made of the silver nanowires has a surface resistivity of 10¹˜10³Ω/□ and a light transmittance of 90% or more to the base film.

Advantageous Effects

When the technology of the present invention is used, silver nanowires having a diameter of less than 100 nm and a length of 10 μm or more can be uniformly prepared in a solution phase. Further, since each of the silver nanowires of the present invention has a large aspect ratio of 100 or more, when a three-dimensional network is formed on the surface of a base film using the silver nanowires, low surface resistivity and high light transmittance can be simultaneously realized.

DESCRIPTION OF DRAWINGS

FIGS. 1 and 2 are scanning electron microscope photographs showing the silver nanowires and silver nanoparticles of Comparative Example 1, respectively.

FIG. 3 is an electron microscope photograph showing the silver nanowires of Example 1.

FIG. 4 is an electron microscope photograph showing the silver nanowires of Example 2.

FIG. 5 is an electron microscope photograph showing the silver nanowires of Example 3.

FIG. 6 is an electron microscope photograph showing the silver nanoparticles of Comparative Example 2.

MODE FOR INVENTION

Hereinafter, the present invention will be described in more detail with reference to the following Examples. However, these Examples are set forth to illustrate the present invention, and the scope of the present invention is not limited thereto.

Comparative Example 1

Preparation of Silver Nanowires Using Polyol Reaction

0.1 mol (17 g) of AgNO₃(manufactured by Kojima Co., Ltd., purity: 99.99%) and 0.15 mol (16.7 g) of PVP (manufactured by Aldrich Corporation, weight average molecular weight: 55,000 g/mol) were put into a 2 L round-bottom flask, dissolved in 1 L of ethyleneglycol (EG), and then stirred at room temperature for 10 minutes to obtain a transparent mixed solution. The color of the mixed solution became gray brown as soon as the mixed solution was reacted at 150° C. for about 30 minutes. Subsequently, the mixed solution was cooled to room temperature, filtered by a filter having a pore size of 1 μm, dried, and then observed using a scanning electron microscope. As shown in the photographs of FIGS. 1 and 2, it was observed that silver nanowires having a diameter of 90˜120 nm and a length of 5˜20 μm were formed, but the diameters of the silver nanowires were somewhat large and not uniform. Further, it was observed that silver nanoparticles having a particle size of 0.5˜5 μm were formed together with the silver nanowires.

Example 1

Preparation of Silver Nanowires Using Ionic Liquid Containing Chlorine Ion (Cl⁻) as Additive in Polyol Reaction

0.1 mol of AgNO₃, 0.15 mol of PVP and 0.001 mol of 1-ethyl-3-methylimidazolium chloride (EMIM-Cl) were dissolved in 1 L of ethyleneglycol (EG), and were then stirred at room temperature for 10 minutes to obtain a transparent mixed solution. The color of the mixed solution became gray as soon as the mixed solution was reacted at 150° C. for about 30 minutes. Subsequently, the mixed solution was cooled to room temperature, filtered by a filter having a pore size of 1 μm, dried, and then observed using a scanning electron microscope. As shown in the photograph of FIG. 3, it was observed that silver nanowires having a diameter of 55˜65 nm and a length of 10˜30 μm were uniformly formed. Further, it was observed that, differently from the results of Comparative Example 1 in which an ionic liquid was not used, silver nanoparticles having different shapes from the silver nanowires were not discovered.

Example 2

Example 2 is the same as Example 1, except that 0.001 mol of 1-butyl-3-methylimidazolium chloride (BMIM-Cl) was used as an ionic liquid. As shown in the photograph of FIG. 4, it was observed that silver nanowires having a diameter of 55˜65 nm were uniformly formed. Further, it was observed that, similarly to the results of Example 1, silver nanoparticles having different shapes from the silver nanowires were not discovered. Comparing the results of Example 2 with the results of Example 1, it was observed that the shapes of silver nanowires were not changed or were only slightly changed depending on the length of an alkyl group of an imidazolium-based ionic liquid having a cation.

Example 3

Preparation of Silver Nanowires Using Ionic Liquid Containing Bromine Ion (Br⁻) as Additive in Polyol Reaction

Example 3 is the same as Example 2, except that 0.001 mol of 1-butyl-3-methylimidazolium bromide (BMIM-Br) was used as an ionic liquid. As shown in the photograph of FIG. 5, it was observed that silver nanowires having a diameter of about 30 nm were uniformly formed. Further, it was observed that, similarly to the results of Example 1, silver nanoparticles having different shapes from the silver nanowires were not discovered. Comparing the results of Example 3 with the results of Example 2, it was observed that the shapes and diameters of silver nanowires were changed depending on the anion of the ionic liquid.

Comparative Example 2

Comparative Example 2 is the same as Example 2, except that 1-butyl-3-methylimidazolium methyl sulfate (BMIM-MeSO₄) was used as an ionic liquid. When the anion of an ionic liquid was Cl— or Br— as in Examples 2 and 3, silver nanowires were formed. In contrast, when the anion of an ionic liquid was CH₃SO₄ ⁻ as in Comparative Example 2, as shown in the photograph of FIG. 6, it can be ascertained that three-dimensional silver nanoparticles, not one-dimensional silver nanowires, were formed.

Example 4

Manufacture of Transparent Conductive Film Using Silver Nanowires Having High Aspect Ratio

0.7 parts by weight of the silver nanowires prepared in Example 2, 98.8 parts by weight of iso-propyl alcohol and 0.5 parts by weight of a cellulose-based thickener were mixed, and were then ultrasonically dispersed to prepare a silver nanowire-dispersed solution. Subsequently, the silver nanowire-dispersed solution was applied onto a polyethylene terephthalate film (thickness: 125 μm) coated with an acrylic adhesion enhancing layer using a bar coater, and was then dried at a temperature of about 100° C. for 1 minute to form a transparent conductive film. The surface resistivity of the transparent conductive film was measured using a four-probe method (AIT Corporation). As a result, the surface resistivity thereof was about 95Ω/□. Further, the light transmittance of the transparent conductive film was measured using a UV-Vis-NIR spectrophotometer (Cary 5000). As a result, the light transmittance of the transparent conductive film to the base film was 94.7%.

INDUSTRIAL APPLICABILITY

The silver nanowires can be used as a main raw material of a touch screen panel which is an important component of various types of electric, electronic and communication appliances, such as smart phones, tablet computers, televisions, etc.

Claims

1. A method of preparing silver nanowires by a polyol reduction reaction of a mixed solution including a silver salt precursor, a reducing solvent and a capping agent,

wherein the polyol reduction reaction of the mixed solution is performed by adding an ionic liquid to the mixed solution as an additive,

wherein the ionic liquid is a compound comprising an organic cation having an imidazolium group and an organic or inorganic anion, the compound being represented by Formula 1 below in the form of a monomer or being represented by Formula 2 below in the form of a polymer:

where R1, R2 and R3 are identical to or different from each other, each of which is hydrogen or a hydrocarbon group of 1 to 16 carbon atoms, and each of which includes at least one heteroatom selected from the group consisting of oxygen, sulfur, nitrogen, phosphorus, fluorine, chlorine, bromine, iodine and silicon; X— is an anion, and is an organic or inorganic compound including a halogen ion such as a chlorine ion (Cl⁻) or a bromine ion (Br⁻); and n is a repetitive unit, and is a natural number.

2. (canceled)

3. The method of claim 1, wherein, in the ionic liquid, the monomeric cationic compound is selected from the group consisting of 1,3-dimethylimidazolium, 1,3-diethylimidazolium, 1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, 1-octyl-3-methylimidazolium, 1-decyl-3-methylimidazolium, 1-dodecyl-3-methylimidazolium and 1-tetradecyl-3-imidazolium, and the polymeric cationic compound is selected from the group consisting of poly(1-vinyl-3-alkylimidazolium), poly(1-allyl-3-alkylimidazolium) and poly(1-(meth)acryloyloxy-3-alkylimidazolium).

4. The method of claim 3, wherein, in a mixing ratio of a silver salt precursor, a capping agent and an ionic liquid, the capping agent is included in an amount of 1 to 2 mol based on 1 mol of the silver salt precursor, and the ionic liquid is included in an amount of 0.001 to 0.2 mol based on 1 mol of the silver salt precursor.

5. The method of claim 4, wherein a reaction temperature for synthesizing silver nanowires is 50˜180° C.

6. The method of claim 5 wherein the silver salt precursor includes a silver cation and an organic or inorganic anion, and includes at least one selected from the group consisting of AgNO₃, AgClO₄, AgBF₄, AgPF₆, CH₃COOAg, AgCF₃SO₃, Ag₂SO₄, CH₃COCH═COCH₃Ag.

7. The method of claim 1, wherein the reducing solvent is a solvent including diol, polyol or glycol having two or more hydroxy groups in a molecule thereof.

8. The method of claim 5, wherein the capping agent is polyvinylpyrrolidone (PVP) or polyvinylalcohol (PVA).

9. (canceled)

10. A silver nanowire-dispersed solution prepared by dispersing 0.1˜5 wt % of the silver nanowires having an aspect ratio of 100 or more, prepared by the method of claim 1 in 95˜99.9 wt % of a solvent.

11. The silver nanowire-dispersed solution of claim 10, wherein the solvent includes at least one selected from the group consisting of water, methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butanol, iso-butanol, hexanol, benzyl alcohol, diacetone alcohol, ethyleneglycol, propyleneglycol, glycerol, 1,4-dioxane, tetrahydrofuran (THF), ethyleneglycol monomethyl ether, ethylenglycol monoethyl ether, ethyleneglycol dimethyl ether, propyleneglycol monomethyl ether, propyleneglycol monoethyl ether, propyleneglycol dimethyl ether, N,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide (DMA), acetonitrile, acetaldehyde, N-methyl-2-pyrrolidone, 2-pyrrolidone, N-vinyl-2-pyrrolidone, dimethylsulfoxide, n-butyrolactone, nitromethane, and ethyl lactate.

12. The silver nanowire-dispersed solution of claim 11, further comprising 0.01 to 10 parts by weight of a dispersant and 0.01 to 10 parts by weight of a thickener based on 100 parts by weight of the silver nanowire-dispersed solution.

13. The silver nanowire-dispersed solution of claim 12, wherein the dispersant includes at least one selected from the group consisting of polyoxyethylene aliphatic ether, polyoxyethylene phenyl ether, polyimine, alkyl phosphate, an alkylammonium salt, a polyester alkylolammonium salt, a polyacrylic alkylolammonium salt, polydimethylsilane, polyacrylic acid, polysulfonic acid and polyvinylpyrrolidone, and the thickener includes at least one selected from the group consisting of a urethane-modified thickener, an acrylic thickener, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose.

14. A transparent conductive film formed by applying the silver nanowire-dispersed solution including the silver nanowires prepared by the method of claim 1 onto a base film.

15. The transparent conductive film of claim 14, wherein the transparent conductive film has a surface resistivity of 10¹˜10Ω/□ and a light transmittance of 90% or more to the base film.

16. The method of claim 3, wherein the reducing solvent is a solvent including diol, polyol or glycol having two or more hydroxy groups in a molecule thereof.

17. The method of claim 4, wherein the reducing solvent is a solvent including diol, polyol or glycol having two or more hydroxy groups in a molecule thereof.

18. The method of claim 5, wherein the reducing solvent is a solvent including diol, polyol or glycol having two or more hydroxy groups in a molecule thereof.

19. The method of claim 6, wherein the reducing solvent is a solvent including diol, polyol or glycol having two or more hydroxy groups in a molecule thereof.

20. A silver nanowire-dispersed solution prepared by dispersing 0.1˜5 wt % of the silver nanowires having an aspect ratio of 100 or more, prepared by the method of claim 7 in 95˜99.9 wt % of a solvent.

21. The silver nanowire-dispersed solution of claim 20, further comprising 0.01 to 10 parts by weight of a dispersant and 0.01 to 10 parts by weight of a thickener based on 100 parts by weight of the silver nanowire-dispersed solution.

22. The silver nanowire-dispersed solution of claim 21, wherein the dispersant includes at least one selected from the group consisting of polyoxyethylene aliphatic ether, polyoxyethylene phenyl ether, polyimine, alkyl phosphate, an alkylammonium salt, a polyester alkylolammonium salt, a polyacrylic alkylolammonium salt, polydimethylsilane, polyacrylic acid, polysulfonic acid and polyvinylpyrrolidone, and the thickener includes at least one selected from the group consisting of a urethane-modified thickener, an acrylic thickener, methylcellulose, ethylcellulose, hydroxyethylcellulose, hydroxymethylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose.