JP7389517B2 - Method for liquefying metal nanoparticles - Google Patents

Description

The present invention relates to a method for liquefying metal nanoparticles.

In recent years, electronic devices including mobile devices have made remarkable progress. Electronic devices are required to be smaller, thinner, lighter, more flexible, and moreover, they are also required to be more productive. BACKGROUND ART Requirements for electronic components such as semiconductor devices have become stricter, and various innovations and improvements are also required for the wiring of these devices.
In such a situation, if there is a material that allows wiring to be formed at a temperature close to room temperature, not only heat-resistant materials but also various non-heat-resistant organic materials can be used as wiring substrates. With the progress of inkjet and dispenser printing technologies, nano-sized metal particles are currently being studied as one such material (see, for example, Non-Patent Document 1). However, since conventional metal fine particles are formed into metal using a sintering reaction, they must be processed at a temperature of at least about 150° C., and their range of use is limited. Under these circumstances, there is a need for materials that allow wiring to be formed at even lower temperatures.
Further, Patent Document 1 discloses that silver oxalate and oleylamine are reacted to form a complex compound, and this is thermally decomposed to obtain ultrafine silver particles. However, when forming conductive films etc. using these ultrafine silver particles, a sintering reaction is used, so the processing temperature is a high temperature of 500℃ or less, and the range of use is limited to a narrow range, and further low-temperature sintering is required. A possible method is needed.
Furthermore, Patent Document 2 discloses that a polar solvent or a polar solvent solution containing a solubilizing agent is applied to a metal nanoparticle paste containing coated metal nanoparticles and a dispersion solvent to sinter the metal nanoparticles, A method of forming wiring on a substrate is disclosed. However, since this method also uses metal sintering, there is a problem that the electrical resistivity of the formed wiring is high and there is large variation.In addition, the low temperature sintering method has a problem that the adhesion strength of the metal to the substrate is low. There are also problems.

Japanese Patent Application Publication No. 2008-214695 Japanese Patent Application Publication No. 2008-072052

Mitsuru Kawase et al., "Nanoparticle fine interconnection technology for Printed Electronics", Shurin, No. 50 (2006/2007), p. 27-31

The present invention has been made in view of the above, and provides a method for easily liquefying metal nanoparticles without the need to sinter metal nanoparticles at high temperatures, and a method for easily forming metals on various base materials. The purpose is to provide a method to do so.

As a result of extensive research in order to achieve the above object, the present inventors have discovered that metal nanoparticles can be produced by utilizing the dynamic chemical equilibrium of surface-protected metal nanoparticles, which are metal nanoparticles whose surfaces are protected with protective molecules. We have discovered a method to easily liquefy In other words, in a system containing metal nanoparticles, protective molecules, and surface-protected metal nanoparticles, there is a dynamic chemical equilibrium in which protective molecules adsorb and desorb to metal nanoparticles depending on the environment, and when surface-protected metal nanoparticles are stored, We have discovered that the above object can be achieved by controlling the equilibrium point in the direction of adsorption of the protective molecule and moving the equilibrium point in the direction of desorption of the protective molecule during metal formation, and have completed the present invention.

〔式中、（Ｓｉｔｅ－ＰＭ）は保護分子が吸着している金属原子の吸着サイトを示し、（Ｓｉｔｅ）は保護分子が吸着していない金属原子の吸着サイトを示し、（ＰＭ）は遊離の保護分子を示す。〕
前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程を含み、
（３）前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程が、下記（ａ）及び／又は（ｂ）の工程
（ａ）前記分散液に含まれる分散媒を構成する種類及び／又はその構成割合を変える、及び／又は、前記分散液の温度を変えることにより、下記式（ＩＩ）：
Ｋｄ＝｛［Ｓｉｔｅ］ｅｑ［ＰＭ］ｅｑ｝／［Ｓｉｔｅ－ＰＭ］ｅｑ （ＩＩ）
〔式中、［Ｓｉｔｅ］ｅｑは平衡状態における保護分子が吸着していない金属原子の吸着サイト濃度（mol/L）を示し、［ＰＭ］ｅｑは平衡状態における遊離の保護分子の濃度（mol/L）を示し、［Ｓｉｔｅ－ＰＭ］ｅｑは平衡状態における保護分子が吸着している金属原子の吸着サイト濃度（mol/L）を示す。〕
で表される保護分子の脱着平衡定数（Ｋｄ）を増大させる工程、
（ｂ）前記分散液に溶媒及び／又は表面保護金属ナノ粒子を添加し、前記式（ＩＩ）における３つの濃度のうちの少なくとも１つを変化させて、前記式（Ｉ）の化学平衡が成り立たない非平衡状態とする工程、
を含む、金属ナノ粒子を液状化する方法。
２．金属ナノ粒子を液状化する方法であって、
（１）前記金属ナノ粒子は、遷移金属ナノ粒子の表面に保護分子が被覆した表面保護金属ナノ粒子の状態で分散液中に分散されており、
（２）前記分散液を基材に塗布し、前記分散液が塗布された基材を溶媒に接触させる工程を含み、
（３）前記分散液が塗布された基材を溶媒に接触させた際に、前記表面保護金属ナノ粒子、金属ナノ粒子及び保護分子の間に、下記式（Ｉ）で表される化学平衡が成り立ち、

〔式中、（Ｓｉｔｅ－ＰＭ）は保護分子が吸着している金属原子の吸着サイトを示し、（Ｓｉｔｅ）は保護分子が吸着していない金属原子の吸着サイトを示し、（ＰＭ）は遊離の保護分子を示す。〕
前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程を含み、
（４）前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程が、下記（ａ’）及び／又は（ｂ’）の工程
（ａ’）前記溶媒の種類及び／又はその構成割合を変える、及び／又は、前記溶媒及び／又は基材の温度を変えることにより、下記式（ＩＩ）：
Ｋｄ＝｛［Ｓｉｔｅ］ｅｑ［ＰＭ］ｅｑ｝／［Ｓｉｔｅ－ＰＭ］ｅｑ （ＩＩ）
〔式中、［Ｓｉｔｅ］ｅｑは平衡状態における保護分子が吸着していない金属原子の吸着サイト濃度（mol/L）を示し、［ＰＭ］ｅｑは平衡状態における遊離の保護分子の濃度（m
ol/L）を示し、［Ｓｉｔｅ－ＰＭ］ｅｑは平衡状態における保護分子が吸着している金属原子の吸着サイト濃度（mol/L）を示す。〕
で表される保護分子の脱着平衡定数（Ｋｄ）を増大させる工程、
（ｂ’）前記溶媒に、溶媒及び／又は表面保護金属ナノ粒子を添加して、前記式（ＩＩ）における３つの濃度のうちの少なくとも１つを変化させて、前記式（Ｉ）の化学平衡が成り立たない非平衡状態とする工程、
を含む、金属ナノ粒子を液状化する方法。
３．前記金属ナノ粒子の平均粒径が１～３０ｎｍである上記項１又は２に記載の方法。
４．前記遷移金属ナノ粒子を構成する遷移金属は、周期表第１０族～第１１族で且つ第４周期～第６周期に属する元素の少なくとも一種である、上記項１～３のいずれか一項に記載の方法。
５．前記遷移金属ナノ粒子を構成する遷移金属は、金、銀、銅、白金及びパラジウムからなる群から選択される少なくとも一種である、上記項１～４のいずれか一項に記載の方法。
６．前記保護分子は、アミノ基及びカルボキシル基の少なくとも一種を含有する、上記項１～５のいずれか一項に記載の方法。
７．基材に金属を形成する方法であって、
（１）金属ナノ粒子を含有する分散液に、基材を接触させる工程を含み、
（２）前記金属ナノ粒子は、遷移金属ナノ粒子の表面に保護分子が被覆した表面保護金属ナノ粒子の状態で前記分散液中に分散されており、
（３）前記表面保護金属ナノ粒子、金属ナノ粒子及び保護分子の間に、下記式（Ｉ）で表される化学平衡が成り立ち、

〔式中、（Ｓｉｔｅ－ＰＭ）は保護分子が吸着している金属原子の吸着サイトを示し、（Ｓｉｔｅ）は保護分子が吸着していない金属原子の吸着サイトを示し、（ＰＭ）は遊離の保護分子を示す。〕
前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程を含み、
（４）前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程が、下記（ａ）及び／又は（ｂ）の工程
（ａ）前記分散液に含まれる分散媒を構成する種類及び／又はその構成割合を変える、及び／又は、前記分散液の温度を変えることにより、下記式（ＩＩ）：
Ｋｄ＝｛［Ｓｉｔｅ］ｅｑ［ＰＭ］ｅｑ｝／［Ｓｉｔｅ－ＰＭ］ｅｑ （ＩＩ）
〔式中、［Ｓｉｔｅ］ｅｑは平衡状態における保護分子が吸着していない金属原子の吸着サイト濃度（mol/L）を示し、［ＰＭ］ｅｑは平衡状態における遊離の保護分子の濃度（mol/L）を示し、［Ｓｉｔｅ－ＰＭ］ｅｑは平衡状態における保護分子が吸着している金属原子の吸着サイト濃度（mol/L）を示す。〕
で表される保護分子の脱着平衡定数（Ｋｄ）を増大させる工程、
（ｂ）前記分散液に溶媒及び／又は表面保護金属ナノ粒子を添加し、前記式（ＩＩ）における３つの濃度のうちの少なくとも１つを変化させて、前記式（Ｉ）の化学平衡が成り立たない非平衡状態とする工程、
を含む、基材に金属を形成する方法。
８．基材に金属を形成する方法であって、
（１）金属ナノ粒子を含有する分散液を基材に塗布し、前記分散液が塗布された基材を溶媒に接触させる工程を含み、
（２）前記金属ナノ粒子は、遷移金属ナノ粒子の表面に保護分子が被覆した表面保護金属ナノ粒子の状態で前記分散液中に分散されており、
（３）前記分散液が塗布された基材を溶媒に接触させた際に、前記表面保護金属ナノ粒子、金属ナノ粒子及び保護分子の間に、下記式（Ｉ）で表される化学平衡が成り立ち、

〔式中、（Ｓｉｔｅ－ＰＭ）は保護分子が吸着している金属原子の吸着サイトを示し、（Ｓｉｔｅ）は保護分子が吸着していない金属原子の吸着サイトを示し、（ＰＭ）は遊離の保護分子を示す。〕
前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程を含み、
（４）前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程が、下記（ａ’）及び／又は（ｂ’）の工程
（ａ’）前記溶媒の種類及び／又はその構成割合を変える、及び／又は、前記溶媒及び／又は基材の温度を変えることにより、下記式（ＩＩ）：
Ｋｄ＝｛［Ｓｉｔｅ］ｅｑ［ＰＭ］ｅｑ｝／［Ｓｉｔｅ－ＰＭ］ｅｑ （ＩＩ）
〔式中、［Ｓｉｔｅ］ｅｑは平衡状態における保護分子が吸着していない金属原子の吸着サイト濃度（mol/L）を示し、［ＰＭ］ｅｑは平衡状態における遊離の保護分子の濃度（mol/L）を示し、［Ｓｉｔｅ－ＰＭ］ｅｑは平衡状態における保護分子が吸着している金属原子の吸着サイト濃度（mol/L）を示す。〕
で表される保護分子の脱着平衡定数（Ｋｄ）を増大させる工程、
（ｂ’）前記溶媒に、溶媒及び／又は表面保護金属ナノ粒子を添加して、前記式（ＩＩ）における３つの濃度のうちの少なくとも１つを変化させて、前記式（Ｉ）の化学平衡が成り立たない非平衡状態とする工程、
を含む、基材に金属を形成する方法。
９．金、銀、銅、白金及びパラジウムからなる群から選択される少なくとも一種から構成され、平均粒径が１～３０ｎｍである金属ナノ粒子の表面に、
アミノ基及びカルボキシル基の少なくとも一種を含有する保護分子が被覆した表面保護金属ナノ粒子が、
無極性溶媒を含む分散媒に分散されている分散液。 That is, the present invention relates to a method of liquefying metal nanoparticles, a method of forming metal on a substrate, and a dispersion described below.
1. A method for liquefying metal nanoparticles, the method comprising:
(1) The metal nanoparticles are dispersed in the dispersion in the form of surface-protected metal nanoparticles in which the surface of transition metal nanoparticles is coated with protective molecules,
(2) A chemical equilibrium represented by the following formula (I) is established between the surface-protected metal nanoparticles, metal nanoparticles, and protective molecules,

[In the formula, (Site-PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed, (Site) represents the adsorption site of the metal atom to which the protective molecule is not adsorbed, and (PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed. Indicates a protective molecule. ]
Shifting the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule,
(3) The step of moving the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule includes the following steps (a) and/or (b): By changing the composition ratio thereof and/or changing the temperature of the dispersion, the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq (II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
A step of increasing the desorption equilibrium constant (Kd) of the protective molecule expressed by
(b) A solvent and/or surface-protected metal nanoparticles are added to the dispersion liquid, and at least one of the three concentrations in the formula (II) is changed, so that the chemical equilibrium of the formula (I) is established. A process of bringing about a non-equilibrium state,
A method of liquefying metal nanoparticles, comprising:
2. A method for liquefying metal nanoparticles, the method comprising:
(1) The metal nanoparticles are dispersed in the dispersion in the form of surface-protected metal nanoparticles in which the surface of transition metal nanoparticles is coated with protective molecules,
(2) comprising the step of applying the dispersion to a substrate and bringing the substrate coated with the dispersion into contact with a solvent;
(3) When the base material coated with the dispersion liquid is brought into contact with a solvent, a chemical equilibrium expressed by the following formula (I) is established between the surface-protected metal nanoparticles, metal nanoparticles, and protective molecules. established,

[In the formula, (Site-PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed, (Site) represents the adsorption site of the metal atom to which the protective molecule is not adsorbed, and (PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed. Indicates a protective molecule. ]
Shifting the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule,
(4) The step of moving the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule is the step (a') of the following (a') and/or (b'): Type of the solvent and/or its constituent ratio and/or by changing the temperature of the solvent and/or the base material, the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq (II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (m
ol/L), and [Site-PM]eq indicates the adsorption site concentration (mol/L) of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
A step of increasing the desorption equilibrium constant (Kd) of the protective molecule expressed by
(b') Adding a solvent and/or surface-protected metal nanoparticles to the solvent to change at least one of the three concentrations in the formula (II) to achieve chemical equilibrium of the formula (I). A process of creating a non-equilibrium state where
A method of liquefying metal nanoparticles, comprising:
3. 3. The method according to item 1 or 2 above, wherein the metal nanoparticles have an average particle size of 1 to 30 nm.
4. The transition metal constituting the transition metal nanoparticles is at least one of the elements belonging to Groups 10 to 11 of the periodic table and belonging to the 4th to 6th periods, according to any one of items 1 to 3 above. Method described.
5. 5. The method according to any one of items 1 to 4 above, wherein the transition metal constituting the transition metal nanoparticles is at least one selected from the group consisting of gold, silver, copper, platinum, and palladium.
6. 6. The method according to any one of items 1 to 5 above, wherein the protective molecule contains at least one of an amino group and a carboxyl group.
7. A method of forming metal on a base material, the method comprising:
(1) including a step of bringing the base material into contact with a dispersion containing metal nanoparticles,
(2) the metal nanoparticles are dispersed in the dispersion in the form of surface-protected metal nanoparticles in which the surface of transition metal nanoparticles is coated with protective molecules;
(3) A chemical equilibrium represented by the following formula (I) is established between the surface-protected metal nanoparticles, metal nanoparticles, and protective molecules,

[In the formula, (Site-PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed, (Site) represents the adsorption site of the metal atom to which the protective molecule is not adsorbed, and (PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed. Indicates a protective molecule. ]
Shifting the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule,
(4) The step of moving the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule includes the following steps (a) and/or (b): By changing the composition ratio thereof and/or changing the temperature of the dispersion, the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq (II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
A step of increasing the desorption equilibrium constant (Kd) of the protective molecule expressed by
(b) A solvent and/or surface-protected metal nanoparticles are added to the dispersion liquid, and at least one of the three concentrations in the formula (II) is changed, so that the chemical equilibrium of the formula (I) is established. A process of bringing about a non-equilibrium state,
A method of forming a metal on a substrate, including:
8. A method of forming metal on a base material, the method comprising:
(1) A step of applying a dispersion containing metal nanoparticles to a substrate and bringing the substrate coated with the dispersion into contact with a solvent,
(2) the metal nanoparticles are dispersed in the dispersion in the form of surface-protected metal nanoparticles in which the surface of transition metal nanoparticles is coated with protective molecules;
(3) When the base material coated with the dispersion liquid is brought into contact with a solvent, a chemical equilibrium expressed by the following formula (I) is established between the surface-protected metal nanoparticles, metal nanoparticles, and protective molecules. established,

[In the formula, (Site-PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed, (Site) represents the adsorption site of the metal atom to which the protective molecule is not adsorbed, and (PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed. Indicates a protective molecule. ]
Shifting the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule,
(4) The step of moving the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule is the step (a') of the following (a') and/or (b'): Type of the solvent and/or its constituent ratio and/or by changing the temperature of the solvent and/or the base material, the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq (II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
A step of increasing the desorption equilibrium constant (Kd) of the protective molecule expressed by
(b') Adding a solvent and/or surface-protected metal nanoparticles to the solvent to change at least one of the three concentrations in the formula (II) to achieve chemical equilibrium of the formula (I). A process of creating a non-equilibrium state where
A method of forming a metal on a substrate, including:
9. On the surface of metal nanoparticles made of at least one selected from the group consisting of gold, silver, copper, platinum and palladium and having an average particle size of 1 to 30 nm,
Surface-protected metal nanoparticles coated with protective molecules containing at least one of an amino group and a carboxyl group,
A dispersion liquid that is dispersed in a dispersion medium containing a nonpolar solvent.

In the liquefaction method of metal nanoparticles of the present invention, the principle of dynamic chemical equilibrium is applied to the system of metal nanoparticles and protective molecules that are adsorbed molecules, and by changing various conditions, protection from surface-protecting metal nanoparticles is achieved. Metal nanoparticles can be easily liquefied by desorbing molecules. Moreover, the method of forming metal on a base material of the present invention is an excellent method with a very simple and easy manufacturing process.
The liquefaction method and metal forming method of the present invention do not use a method of sintering metal nanoparticles, so there is no need to heat the base material to which the metal nanoparticles are applied to a high temperature, and It can be applied to various base materials including fiber base materials and the like. In addition, since the metal nanoparticles used in the present invention are extremely small, they have a strong ability to penetrate into the interior of objects that are base materials, and liquefied metal can be injected into various base materials, allowing only the surface of the base material to be injected. It is also possible to form metal inside the structure. Furthermore, since metal nanoparticles can be easily liquefied using the method of the present invention, metals can be formed on base materials of various shapes. Therefore, by the liquefaction method and metal forming method of the present invention, metal can be formed on a wide range of polymers, fiber materials, etc. to make them conductive, and metal can be formed into various shapes on a nanoscale.

1 is a TEM image showing that the gold nanoparticles of Example 1 are liquefied (flowing). FIG. 3 is a diagram showing liquefaction of silver nanoparticles in the dispersion liquid of Example 2. 3 is a diagram showing an electron micrograph and an X-ray diffraction result of a metal thin film of Example 3. FIG. FIG. 6 is a diagram showing changes before and after immersing polyurethane in the dispersion liquid of Example 6. FIG. 7 is a diagram showing changes before and after immersing rayon in the dispersion liquid of Example 7.

Hereinafter, the method for liquefying metal nanoparticles of the present invention will be explained in detail.

〔式中、（Ｓｉｔｅ－ＰＭ）は保護分子が吸着している金属原子の吸着サイトを示し、（Ｓｉｔｅ）は保護分子が吸着していない金属原子の吸着サイトを示し、（ＰＭ）は遊離の保護分子を示す。〕
前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程を含み、
（３）前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程が、下記（ａ）及び／又は（ｂ）の工程
（ａ）前記分散液に含まれる分散媒を構成する種類及び／又はその構成割合を変える、及び／又は、前記分散液の温度を変えることにより、下記式（ＩＩ）：
Ｋｄ＝｛［Ｓｉｔｅ］ｅｑ［ＰＭ］ｅｑ｝／［Ｓｉｔｅ－ＰＭ］ｅｑ （ＩＩ）
〔式中、［Ｓｉｔｅ］ｅｑは平衡状態における保護分子が吸着していない金属原子の吸着サイト濃度（mol/L）を示し、［ＰＭ］ｅｑは平衡状態における遊離の保護分子の濃度（mol/L）を示し、［Ｓｉｔｅ－ＰＭ］ｅｑは平衡状態における保護分子が吸着している金属原子の吸着サイト濃度（mol/L）を示す。〕
で表される保護分子の脱着平衡定数（Ｋｄ）を増大させる工程、
（ｂ）前記分散液に溶媒及び／又は表面保護金属ナノ粒子を添加し、前記式（ＩＩ）における３つの濃度のうちの少なくとも１つを変化させて、前記式（Ｉ）の化学平衡が成り立たない非平衡状態とする工程、
を含むことを特徴とするものである。 The method of liquefying metal nanoparticles of the present invention includes:
(1) The metal nanoparticles are dispersed in the dispersion in the form of surface-protected metal nanoparticles in which the surfaces of transition metal nanoparticles are coated with protective molecules;
(2) A chemical equilibrium represented by the following formula (I) is established between the surface-protected metal nanoparticles, metal nanoparticles, and protective molecules,

[In the formula, (Site-PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed, (Site) represents the adsorption site of the metal atom to which the protective molecule is not adsorbed, and (PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed. Indicates a protective molecule. ]
Shifting the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule,
(3) The step of moving the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule includes the following steps (a) and/or (b): By changing the composition ratio thereof and/or changing the temperature of the dispersion, the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq (II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
A step of increasing the desorption equilibrium constant (Kd) of the protective molecule expressed by
(b) A solvent and/or surface-protected metal nanoparticles are added to the dispersion liquid, and at least one of the three concentrations in the formula (II) is changed, so that the chemical equilibrium of the formula (I) is established. A process of bringing about a non-equilibrium state,
It is characterized by including.

In the method of liquefying the metal nanoparticles (first liquefaction method), the metal nanoparticles can be liquefied by desorbing protective molecules from the surface-protected metal nanoparticles in a dispersion liquid.

In this specification, "the metal nanoparticles liquefy" means that the protective molecules adsorbed on the surface-protected metal nanoparticles are desorbed, and when the number of protective molecules adsorbed on the surface of the metal nanoparticles decreases, the metal nanoparticles become liquefied. It means that the metal atoms that make up the nanoparticles change from a fixed "solid" state to a kind of flowing "liquid" state, that is, "flow." In other words, "liquefaction" means that metal atoms change into a liquid-like state and flow.
As the size of metal nanoparticles decreases, the pressure inside the metal nanoparticles increases, so when there are fewer protective molecules on the surface of metal nanoparticles with a small average particle size such as those of the present invention, the metal constituting the metal nanoparticles The atoms are thought to move and flow like a liquid.

Further, when metal nanoparticles and protective molecules are dispersed in a dispersion liquid, the protective molecules are adsorbed on the surface of the metal nanoparticles, even if the number of molecules is small, and the surface-protected metal nanoparticles are formed. In surface-protected metal nanoparticles, the maximum number of protective molecules that can be adsorbed onto the metal nanoparticle surface can take various values depending on the type of metal and the type of protective molecule. When the number of protective molecules adsorbed on the metal nanoparticle surface falls below a certain value (this value can vary depending on the type of metal and the type of protective molecule), the metal atoms that make up the metal nanoparticle becomes liquefied.

In the present invention, metal nanoparticles are composed of transition metals. Further, one metal nanoparticle is a collection of about several tens to several hundred metal atoms.
The transition metal is not particularly limited, but includes, for example, elements belonging to Groups 3 to 12 of the periodic table. From the viewpoint of desorption equilibrium constant, it is preferably at least one element from Group 10 to Group 11 of the periodic table and from Period 4 to Period 6, and from the group consisting of gold, silver, copper, platinum, and palladium. It is more preferable to use at least one selected one.
Here, the viewpoint of the desorption equilibrium constant is to keep the desorption equilibrium constant small when storing the dispersion (before liquefaction), and to increase the desorption equilibrium constant during liquefaction. (the viewpoint that the required amount of protective molecules can be adsorbed on the surface of metal nanoparticles, and that the protective molecules can be easily desorbed from the surface of metal nanoparticles by changing conditions).

From the viewpoint of adsorption/desorption of protective molecules to metal nanoparticles, the average particle size of metal nanoparticles is preferably 1 to 30 nm (nanometers), and as the size of metal nanoparticles becomes smaller, the melting point of metal nanoparticles decreases. From the viewpoint of increasing the size, in order to lower the liquefaction temperature of metal nanoparticles, the diameter is more preferably 2 to 20 nm, even more preferably 2 to 10 nm, and particularly preferably 2 to 6 nm.
By reducing the average particle size of metal nanoparticles, it becomes possible to adsorb protective molecules that cannot be adsorbed by a flat metal plate (the particle size can be considered infinite), and by reducing the particle size, the desorption equilibrium constant can be reduced. It can be set to a large value, and protective molecules can be easily desorbed from the surface of metal nanoparticles by changing the conditions.
The average particle size of the metal nanoparticles can be measured, for example, by image analysis using a transmission electron microscope or a scanning electron microscope. Specifically, it can be measured by the method described in the Examples section.

The protective molecule that coats the surface of the metal nanoparticle is not particularly limited as long as it can coat the surface of the metal nanoparticle, but from the viewpoint of desorption equilibrium constant, it is a compound containing at least one of an amino group and a carboxyl group. It is preferable.
Compounds containing an amino group are not particularly limited, but include, for example, alkylamines having 1 to 30 carbon atoms, alkenylamines having 2 to 30 carbon atoms, alkynylamines having 2 to 30 carbon atoms, arylamines, aralkylamines, etc. Can be mentioned. From the viewpoint of desorption equilibrium constant, alkylamines having 1 to 30 carbon atoms and alkenylamines having 2 to 30 carbon atoms are preferred; alkylamines having 10 to 30 carbon atoms and alkenylamines having 10 to 30 carbon atoms are more preferred; Alkylamines having 10 to 20 carbon atoms and alkenylamines having 10 to 20 carbon atoms are more preferred; dodecylamine, oleylamine and the like are particularly preferred.

Compounds containing carboxyl groups are not particularly limited, but include, for example, alkylcarboxylic acids having 1 to 30 carbon atoms, alkenylcarboxylic acids having 2 to 30 carbon atoms, alkynylcarboxylic acids having 2 to 30 carbon atoms, arylcarboxylic acids, Examples include aralkylcarboxylic acids. From the viewpoint of desorption equilibrium constant, alkyl carboxylic acids having 1 to 30 carbon atoms and alkenyl carboxylic acids having 2 to 30 carbon atoms are preferred; alkyl carboxylic acids having 10 to 30 carbon atoms and alkenyl carboxylic acids having 10 to 30 carbon atoms are more preferred. Preferable; alkylcarboxylic acids having 10 to 20 carbon atoms and alkenylcarboxylic acids having 10 to 20 carbon atoms are more preferable; decanoic acid, dodecylcarboxylic acid, oleylcarboxylic acid and the like are particularly preferable.

The metal nanoparticles are dispersed in the dispersion in the form of surface-protected metal nanoparticles in which the surfaces of the transition metal nanoparticles are coated with protective molecules.
The surface-protected metal nanoparticles are not particularly limited as long as the surfaces of the metal nanoparticles are coated with the protective molecules.
Here, "coated" means that the protective molecules are adsorbed to metal atoms on the surface of the metal nanoparticles, and if a part or all of the surface of the metal nanoparticles is coated with the protective molecules, good.

The dispersion liquid contains a dispersion medium.
The dispersion medium is not particularly limited as long as it can disperse the surface-protected metal nanoparticles, and examples thereof include nonpolar solvents, mixed solvents of nonpolar solvents and polar solvents, and the like.
Note that in this specification, the term "solvent" is used to indicate a medium, regardless of whether or not it has the property of dissolving the medium.

Non-polar solvents include, but are not particularly limited to, alkanes such as pentane, hexane, heptane, octane, and nonane; cycloalkanes such as cyclohexane, cyclopentane, cycloheptane, and cyclooctane; methylene chloride, chloroform, carbon tetrachloride, etc. Alkanes substituted with halogens; Ethers such as diethyl ether and diisopropyl ether; Alcohols with 6 or more carbon atoms such as hexanol, heptanol, and octanol; Aromatic hydrocarbons such as benzene, toluene, and xylene; Complex compounds such as tetrahydrofuran and tetrahydropyran Examples include cyclic compounds. From the viewpoint of desorption equilibrium constant, alkanes, halogen-substituted alkanes, and aromatic hydrocarbons are preferred, and hexane, methylene chloride, and toluene are more preferred.

The polar solvent is not particularly limited as long as it can be mixed with the above-mentioned non-polar solvent, but examples include alcohols having 1 to 5 carbon atoms such as methanol, ethanol, 1-propanol, 2-propanol, butanol, and pentanol. ; amides such as formamide and acetamide; ionic liquids such as 1-ethyl-3-methylimidazolium tetrafluoroborate; and the like. From the viewpoint of desorption equilibrium constant, alcohols having 1 to 3 carbon atoms are preferred, and methanol and ethanol are more preferred.

As mentioned above, the protective molecule is preferably a compound containing a polar group (at least one of an amino group and a carboxyl group), but in that case, the polar group is adsorbed to the surface of the metal nanoparticle, and the non-polar group is It is thought that it faces outside (dispersion medium side).
Therefore, a nonpolar solvent is preferable as a dispersion medium for stably dispersing surface-protected metal nanoparticles in a dispersion during storage.
Furthermore, because of the above structure of the surface-protected metal nanoparticles, the polar solvent has the effect of desorbing protective molecules from the surface-protected metal nanoparticles. Therefore, it is not appropriate to use a polar solvent alone as a dispersion medium, but a mixed solvent of a nonpolar solvent and a polar solvent can be used as a dispersion medium, and liquefaction can be adjusted by adjusting the mixing ratio. .
When using a mixed solvent of a non-polar solvent and a polar solvent, the mixing ratio is not particularly limited, but from the viewpoint of dispersing and preserving the surface-protected metal nanoparticles, it depends on the selection of the non-polar solvent and the polar solvent. When the volume of the non-polar solvent is taken as 100%, the volume of the polar solvent is, for example, 20% or less, preferably 10% or less, more preferably 5% or less, and in both cases, the non-polar solvent is mainly used (solvent volume (more than half of the total).

The method for producing the metal nanoparticles is not particularly limited, but examples include chemical production by reducing a metal salt or a metal complex in a solution.
In addition, the method for producing surface-protected metal nanoparticles in which the surface of metal nanoparticles is coated with protective molecules is not particularly limited, but for example, it can be produced by reducing metal salts or metal complexes in a solution in which protective molecules are dissolved. Examples include:
Furthermore, the method for producing a dispersion liquid in which surface-protected metal nanoparticles are dispersed is not particularly limited, and examples thereof include the following method. Metal salts and metal complexes are reduced in a solution containing protective molecules, nucleating metal nanoparticles and synthesizing seed crystals. From there, metal salts and metal complexes are reduced around the seed crystal, causing the seed crystal to grow larger (nucleus growth). By controlling the reaction by performing nuclear growth multiple times in stages, it is possible to produce a dispersion in which surface-protected metal nanoparticles with an average particle size of 1 to 30 nm are dispersed.

〔式中、（Ｓｉｔｅ－ＰＭ）は保護分子が吸着している金属原子の吸着サイトを示し、（Ｓｉｔｅ）は保護分子が吸着していない金属原子の吸着サイトを示し、（ＰＭ）は遊離の保護分子を示す。〕 In the above dispersion, a chemical equilibrium represented by the following formula (I) is established between the surface-protected metal nanoparticles, the metal nanoparticles, and the protective molecules.

[In the formula, (Site-PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed, (Site) represents the adsorption site of the metal atom to which the protective molecule is not adsorbed, and (PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed. Indicates a protective molecule. ]

More specifically, (Site-PM) indicates an adsorption site of a metal atom on which a protective molecule is adsorbed in the surface-protected metal nanoparticle.
(Site) indicates an adsorption site of a metal atom to which a protective molecule is not adsorbed. This indicates both the metal atom adsorption site of the metal nanoparticle itself and the metal atom adsorption site on the surface-protected metal nanoparticle to which no protective molecules are adsorbed.
(PM) indicates free protective molecules not adsorbed to metal nanoparticles.

The adsorption site for metal atoms means the following.
If the surface of a metal nanoparticle is divided into a grid pattern and it is assumed that one protective molecule can be adsorbed per square, then one square is defined as a metal atom adsorption site. When one protective molecule is adsorbed to a metal nanoparticle, the area occupied by one protective molecule (i.e. the size of one square) depends on the type of protective molecule, the posture in which the protective molecule is adsorbed, etc. It varies depending on the state.

The method of liquefying metal nanoparticles of the present invention includes a step of moving the equilibrium point of the chemical equilibrium of the above formula (I) in the direction of desorption of the protective molecule.
The direction of desorption of the protective molecule is the direction in which the equilibrium point moves to the right in the above formula (I).

The step of moving the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule includes the following steps (a) and/or (b).
(a) By changing the type and/or the composition ratio of the dispersion medium contained in the dispersion liquid, and/or by changing the temperature of the dispersion liquid, the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq (II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
A step of increasing the desorption equilibrium constant (Kd) of the protective molecule expressed by
(b) A solvent and/or surface-protected metal nanoparticles are added to the dispersion liquid, and at least one of the three concentrations in the formula (II) is changed, so that the chemical equilibrium of the formula (I) is established. A process that results in a non-equilibrium state.

Step (a) is a step of increasing the desorption equilibrium constant (Kd) of the protective molecule represented by the above formula (II), and in order to increase Kd, the type constituting the dispersion medium contained in the dispersion liquid is This is a step of changing the composition ratio thereof and/or changing the temperature of the dispersion liquid.

The desorption equilibrium constant (Kd) of the protective molecule is an equilibrium constant when the chemical equilibrium represented by the above formula (I) is established, and is represented by the above formula (II).
[Site] eq indicates the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in an equilibrium state, and [PM] eq indicates the concentration of free protective molecules in an equilibrium state (mol/L). , [Site-PM]eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state.
Each of the above concentrations indicates each concentration (mol/L) in the dispersion, that is, the number of moles (mol) of each component in the volume (L) of the dispersion.

The desorption equilibrium constant (Kd) is a function of temperature, and once the temperature is determined, the value of Kd is determined. Further, even at the same temperature, Kd shows different values depending on the type of solvent. Furthermore, the type, concentration, and temperature of the solvent may be changed so as to increase the desorption equilibrium constant (Kd) and cause liquefaction.
In the liquefaction method of the present invention, the desorption equilibrium constant (Kd) is controlled by the type, concentration, and temperature of the solvent, but the value of the desorption equilibrium constant can also be changed depending on the type of metal nanoparticle, particle size, and type of protective molecule. is possible.
The range of the desorption equilibrium constant (Kd) is not particularly limited, but when increasing Kd to form metal by liquefaction, it is preferably 1×10 ⁻⁴ mol/L or more. This is because when liquefying, the number of molecules adsorbed on the particle surface only needs to be below a certain number, and as the value of Kd increases, the molecules become easier to desorb.
In addition, before liquefaction (when protecting the particle surface with molecules), the number of molecules adsorbed on the particle surface only needs to exceed a certain number, and from the viewpoint of keeping the desorption equilibrium constant (Kd) low, It is preferably 1×10 ⁻² mol/L or less. The desorption equilibrium constant (Kd) may be set within the above range, and liquefaction may be controlled by changing the type, concentration, temperature, etc. of the solvent.

In step (a), the type and/or the composition ratio of the dispersion medium contained in the dispersion liquid is changed, and/or the temperature of the dispersion liquid is changed so as to increase the desorption equilibrium constant (Kd). change.

Methods for changing the type and/or composition ratio of the dispersion medium contained in the dispersion liquid are not particularly limited, but for example, the dispersion medium used in the initial dispersion liquid (hereinafter also referred to as initial dispersion liquid) may be changed. (hereinafter also referred to as initial dispersion medium), addition of a solvent to change the composition ratio of the solvent used as the initial dispersion medium, solvent used as the initial dispersion medium Examples include vaporizing. Thereby, whether the initial dispersion medium is one type of solvent or a mixed solvent of two or more types, the type and composition ratio of the dispersion medium can be changed. Note that from the viewpoint of shifting the equilibrium point in the direction of desorption, it is preferable to add a solvent different from the initial dispersion medium.
In addition, when the initial dispersion medium is a mixed solvent of two or more types, it is necessary to add only one of the solvents used as the initial dispersion medium, or to remove all the solvents used as the initial dispersion medium. The composition ratio of the solvent constituting the dispersion medium can be changed by adding the solvent in a ratio different from that of the initial dispersion medium.

Although the solvent to be added is not particularly limited, it is preferable to use a polar solvent in order to facilitate desorption of the protective molecules.
Examples of polar solvents include, but are not limited to, alcohols having 1 to 5 carbon atoms such as methanol, ethanol, 1-propanol, 2-propanol, butanol, and pentanol; amides such as formamide and acetamide; 1-ethyl-3 - Ionic liquids such as methylimidazolium tetrafluoroborate and the like. From the viewpoint of ease of desorption, alcohols having 1 to 3 carbon atoms are preferred, and methanol and ethanol are more preferred.
Further, when the solvent is vaporized, it can be carried out by leaving it in an open state.

The method of changing the temperature of the dispersion liquid is not particularly limited, and examples thereof include warming the dispersion liquid using a heater such as a heater.
The dispersion during storage before liquefaction is stored, for example, by frozen storage, refrigerated storage, room temperature storage, or the like. Therefore, the temperature of the dispersion during storage is not particularly limited, but is generally -30°C to 35°C.
In the method of changing the temperature of the dispersion, the heating temperature of the dispersion during liquefaction for metal formation is not particularly limited, but is preferably 120°C or lower, more preferably 100°C or lower, and even more preferably 80°C or lower. preferable. Further, the lower limit temperature can be set higher than the above storage temperature. The present invention is characterized in that metal formation can be performed at a lower temperature than in the sintering method. Further, when forming metal on the base material as described below, the temperature can be set within a wide temperature range in consideration of the heat resistance of the base material.
Since Kd usually takes a larger value as the temperature of the dispersion liquid increases, it is preferable to change the temperature of the dispersion liquid by warming the dispersion liquid.

Step (b) is to add a solvent and/or surface-protected metal nanoparticles to the dispersion, change at least one of the three concentrations in the formula (II), and modify the chemical composition of the formula (I). This is a process of creating a non-equilibrium state where equilibrium does not hold.

When adding a solvent to the dispersion liquid, the added solvent may be the same type as the initial dispersion medium or a different type. Further, when the initial dispersion medium is a mixed solvent, the solvent may be added at the same mixing ratio as the initial dispersion medium or at a different mixing ratio.
By adding a solvent to the dispersion, the chemical equilibrium of the formula (I) that had been established up to that point is disrupted, resulting in a non-equilibrium state. However, within the dispersion system, the equilibrium point moves in the direction of desorption of the protective molecule so that the chemical equilibrium of formula (I) is established again.
Although the solvent to be added is not particularly limited, it is preferable to use a polar solvent in order to facilitate desorption of the protective molecules. Examples of the polar solvent include those mentioned above.

When adding surface-protected metal nanoparticles to the dispersion, the surface-protected metal nanoparticles to be added may be the same type as the surface-protected metal nanoparticles that were present in the initial dispersion, or may be of a different type. However, from the viewpoint that the adsorption energy may be distributed and a mixture of particles that flow and particles that maintain a solid state may occur, it is preferable that the particles be of the same type because they can be easily controlled.
By adding surface-protected metal nanoparticles to the dispersion, the chemical equilibrium of the formula (I) that had been established up to that point is disrupted, resulting in a non-equilibrium state. However, within the dispersion system, the equilibrium point moves in the direction of desorption of the protective molecule so that the chemical equilibrium of formula (I) is established again.

〔式中、（Ｓｉｔｅ－ＰＭ）は保護分子が吸着している金属原子の吸着サイトを示し、（Ｓｉｔｅ）は保護分子が吸着していない金属原子の吸着サイトを示し、（ＰＭ）は遊離の保護分子を示す。〕
前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程を含み、
（４）前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程が、下記（ａ’）及び／又は（ｂ’）の工程
（ａ’）前記溶媒の種類及び／又はその構成割合を変える、及び／又は、前記溶媒及び／又は基材の温度を変えることにより、下記式（ＩＩ）：
Ｋｄ＝｛［Ｓｉｔｅ］ｅｑ［ＰＭ］ｅｑ｝／［Ｓｉｔｅ－ＰＭ］ｅｑ （ＩＩ）
〔式中、［Ｓｉｔｅ］ｅｑは平衡状態における保護分子が吸着していない金属原子の吸着サイト濃度（mol/L）を示し、［ＰＭ］ｅｑは平衡状態における遊離の保護分子の濃度（mol/L）を示し、［Ｓｉｔｅ－ＰＭ］ｅｑは平衡状態における保護分子が吸着している金属
原子の吸着サイト濃度（mol/L）を示す。〕
で表される保護分子の脱着平衡定数（Ｋｄ）を増大させる工程、
（ｂ’）前記溶媒に、溶媒及び／又は表面保護金属ナノ粒子を添加して、前記式（ＩＩ）における３つの濃度のうちの少なくとも１つを変化させて、前記式（Ｉ）の化学平衡が成り立たない非平衡状態とする工程、
を含むことを特徴とするものである。 Another method of the present invention is to liquefy metal nanoparticles.
(1) The metal nanoparticles are dispersed in the dispersion in the form of surface-protected metal nanoparticles in which the surface of transition metal nanoparticles is coated with protective molecules,
(2) comprising the step of applying the dispersion to a substrate and bringing the substrate coated with the dispersion into contact with a solvent;
(3) When the base material coated with the dispersion liquid is brought into contact with a solvent, a chemical equilibrium expressed by the following formula (I) is established between the surface-protected metal nanoparticles, metal nanoparticles, and protective molecules. established,

[In the formula, (Site-PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed, (Site) represents the adsorption site of the metal atom to which the protective molecule is not adsorbed, and (PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed. Indicates a protective molecule. ]
Shifting the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule,
(4) The step of moving the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule is the step (a') of the following (a') and/or (b'): Type of the solvent and/or its constituent ratio and/or by changing the temperature of the solvent and/or the base material, the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq (II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
A step of increasing the desorption equilibrium constant (Kd) of the protective molecule expressed by
(b') Adding a solvent and/or surface-protected metal nanoparticles to the solvent to change at least one of the three concentrations in the formula (II) to achieve chemical equilibrium of the formula (I). A process of creating a non-equilibrium state where
It is characterized by including.

The method for liquefying the metal nanoparticles (second liquefaction method) includes applying a dispersion containing surface-protected metal nanoparticles to a base material in the first liquefaction method, and applying the dispersion to a substrate. The method further includes the step of bringing the substrate into contact with a solvent. Specifically, the method further includes the step of applying a dispersion containing surface-protecting metal nanoparticles to a base material, and bringing at least the portion of the base material coated with the dispersion into contact with a solvent.
By including this step, in the method, the metal nanoparticles can be liquefied on the surface of the base material (any location thereof) and further inside the base material (any location thereof).

Examples of the base material include, but are not limited to, thermoplastic resins, thermosetting resins, rubber, natural fibers, synthetic fibers, glass, paper, ceramics, and the like.

Examples of thermoplastic resins include, but are not limited to, polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polycarbonate, polyacetal, polyphenylene oxide, polyamide, polysulfone, fluororesin, polyvinyl chloride, polyvinyl alcohol, and polyvinyl acetate. , poly(meth)acrylic acid, polymethyl methacrylate, cellulose acetate, and the like.
Examples of thermosetting resins include, but are not limited to, phenol resins, urea resins, xylene resins, urea resins, melamine resins, epoxy resins, silicon resins, diallyl phthalate resins, furan resins, aniline resins, acetone-formaldehyde resins, Examples include alkyd resins.

Examples of the rubber include, but are not particularly limited to, natural rubber; polydimethylsiloxane, polyurethane, elastic fibers, and synthetic rubbers such as SBR.
Natural fibers include, but are not particularly limited to, cotton, silk, wool, and the like.
Synthetic fibers include, but are not particularly limited to, polyester, rayon, nylon, and the like.

The method of applying a dispersion containing metal nanoparticles to a substrate (not limited to coating, but also includes various methods such as dipping and spraying) is not particularly limited, and for example, immersing the substrate in the dispersion. Examples include a method of spray coating a dispersion on a substrate, a method of drop casting, a method of spin coating, and a method of dispensing.

When the base material is immersed in the dispersion liquid, the base material coated with the dispersion liquid may be taken out after immersion, dried, and then brought into contact with the solvent, or the base material coated with the dispersion liquid may be brought into contact with the solvent. Although it may be brought into contact with a solvent without drying, drying is preferable.
The method for drying the base material is not particularly limited, but examples include a method of leaving it standing at room temperature, a method of blowing off the liquid with an inert gas such as nitrogen, etc., and a method of leaving it standing at room temperature is preferred.
When a dispersion is spray coated on a substrate, almost no dispersion medium is present on the substrate coated with the dispersion. In this case, there is no need to dry the base material coated with the dispersion liquid, and the base material can be brought into contact with the solvent as it is.

The method of bringing the substrate coated with the dispersion into contact with the solvent is not particularly limited, and for example,
Examples include a method of immersing a base material coated with a dispersion liquid in a solvent.
The solvent used in the step of bringing the substrate coated with the dispersion into contact with a solvent is not particularly limited as long as it has the effect of desorbing protective molecules from the surface-protected metal nanoparticles. For example, polar solvents, polar solvents, etc. and a nonpolar solvent.

Examples of polar solvents include, but are not limited to, alcohols having 1 to 5 carbon atoms such as methanol, ethanol, 1-propanol, 2-propanol, butanol, and pentanol; amides such as formamide and acetamide; 1-ethyl-3 - Ionic liquids such as methylimidazolium tetrafluoroborate and the like. From the viewpoint of desorption equilibrium constant, alcohols having 1 to 3 carbon atoms are preferred, and methanol and ethanol are more preferred.

The non-polar solvent is not particularly limited as long as it can be used in combination with the above polar solvent, but examples include alkanes such as heptane, hexane, pentane, octane, and nonane; cyclohexane, cyclopentane, cycloheptane, and cyclooctane; Cycloalkanes; alkanes substituted with halogens such as methylene chloride, chloroform, and carbon tetrachloride; ethers such as diethyl ether and diisopropyl ether; alcohols with 6 or more carbon atoms such as hexanol, heptanol, and octanol; Aromatic hydrocarbons include heterocyclic compounds such as tetrahydrofuran and tetrahydropyran. From the viewpoint of desorption equilibrium constant, alkanes, halogen-substituted alkanes, and aromatic hydrocarbons are preferred, and hexane, methylene chloride, and toluene are more preferred.

The nonpolar solvent has the effect of dispersing the surface-protected metal nanoparticles. Therefore, it is not preferable to use a nonpolar solvent alone as a solvent in this step, but a mixed solvent of a polar solvent and a nonpolar solvent can be used as a solvent in this step.
When using a mixed solvent of a polar solvent and a non-polar solvent, the mixing ratio is not particularly limited. The volume of the polar solvent is, for example, 40% or less, preferably 30% or less, and more preferably 20% or less, and each of them is configured to mainly contain a polar solvent (more than half of the total solvent volume).

In this method, the chemical equilibrium of the above formula (I) is established in a system in which a substrate coated with a dispersion containing surface-protected metal nanoparticles is brought into contact with a solvent. The method is characterized in that the step of moving the equilibrium point of chemical equilibrium in the direction of desorption of the protective molecule includes the steps (a') and/or (b') above.
Regarding step (a') and step (b'), in step (a) and step (b) in the first liquefaction method, the base material is brought into contact with the solvent instead of being liquefied in the dispersion liquid. It can be carried out in the same manner except that it is liquefied. In this second liquefaction method, the base material can be liquefied at any location.
Further, when changing the temperature of the solvent and/or the base material, the temperature of the solvent and the temperature of the base material are not particularly limited, but are each within the same temperature range as the heating temperature of the dispersion liquid in the first liquefaction method. can be used.

In addition, the concentration of each component in the desorption equilibrium constant (Kd) of the protective molecule represented by the above formula (II) is the concentration (mol/ L), that is, the number of moles (mol) of each component in the volume (L) of the solvent with which the substrate coated with the dispersion is brought into contact.

Other liquefaction methods can also be used in the present invention. As another liquefaction method, in (2) of the above-mentioned second liquefaction method, instead of "the step of applying the dispersion liquid to a base material and bringing the base material coated with the dispersion liquid into contact with a solvent" The method includes "the step of adding the dispersion liquid to a solvent".
In this method, by adding (for example, dropping) a dispersion liquid into a solvent, the surface of the metal nanoparticles in the dispersion liquid is liquefied, and the metal nanoparticles gather together.
Examples of the solvent used include the same solvents as those exemplified in the second liquefaction method.

〔式中、（Ｓｉｔｅ－ＰＭ）は保護分子が吸着している金属原子の吸着サイトを示し、（Ｓｉｔｅ）は保護分子が吸着していない金属原子の吸着サイトを示し、（ＰＭ）は遊離の保護分子を示す。〕
前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程を含み、
（４）前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程が、下記（ａ）及び／又は（ｂ）の工程
（ａ）前記分散液に含まれる分散媒を構成する種類及び／又はその構成割合を変える、及び／又は、前記分散液の温度を変えることにより、下記式（ＩＩ）：
Ｋｄ＝｛［Ｓｉｔｅ］ｅｑ［ＰＭ］ｅｑ｝／［Ｓｉｔｅ－ＰＭ］ｅｑ （ＩＩ）
〔式中、［Ｓｉｔｅ］ｅｑは平衡状態における保護分子が吸着していない金属原子の吸着サイト濃度（mol/L）を示し、［ＰＭ］ｅｑは平衡状態における遊離の保護分子の濃度（mol/L）を示し、［Ｓｉｔｅ－ＰＭ］ｅｑは平衡状態における保護分子が吸着している金属原子の吸着サイト濃度（mol/L）を示す。〕
で表される保護分子の脱着平衡定数（Ｋｄ）を増大させる工程、
（ｂ）前記分散液に溶媒及び／又は表面保護金属ナノ粒子を添加し、前記式（ＩＩ）における３つの濃度のうちの少なくとも１つを変化させて、前記式（Ｉ）の化学平衡が成り立たない非平衡状態とする工程、
を含むことを特徴とするものである。 Next, the method of forming metal on the base material in the present invention is as follows:
(1) including a step of bringing the base material into contact with a dispersion containing metal nanoparticles,
(2) the metal nanoparticles are dispersed in the dispersion in the form of surface-protected metal nanoparticles in which the surface of transition metal nanoparticles is coated with protective molecules;
(3) A chemical equilibrium represented by the following formula (I) is established between the surface-protected metal nanoparticles, metal nanoparticles, and protective molecules,

[In the formula, (Site-PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed, (Site) represents the adsorption site of the metal atom to which the protective molecule is not adsorbed, and (PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed. Indicates a protective molecule. ]
Shifting the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule,
(4) The step of moving the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule includes the following steps (a) and/or (b): By changing the composition ratio thereof and/or changing the temperature of the dispersion, the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq (II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
A step of increasing the desorption equilibrium constant (Kd) of the protective molecule expressed by
(b) A solvent and/or surface-protected metal nanoparticles are added to the dispersion liquid, and at least one of the three concentrations in the formula (II) is changed, so that the chemical equilibrium of the formula (I) is established. A process of bringing about a non-equilibrium state,
It is characterized by including.

In the method of forming metal on the base material (first metal forming method), metal can be formed on the surface or inside of the base material in the dispersion liquid.

The step of bringing the substrate into contact with a dispersion containing metal nanoparticles is not particularly limited, and includes, for example, a method of immersing the substrate in a dispersion.

When the base material is immersed in the dispersion liquid, by including a step of moving the equilibrium point of the chemical equilibrium represented by formula (I) in the direction of desorption of the protective molecule, the base material can be immersed in the dispersion liquid without removing the base material from the dispersion liquid. In the dispersion, metal can be formed on the surface of the substrate, or on and inside the substrate.

The various components in the dispersion are as described above. Moreover, the same base materials as those mentioned above can be mentioned as well. Furthermore, a chemical equilibrium represented by the above formula (I) is established in a system in which a base material is brought into contact with a dispersion containing metal nanoparticles.
The steps (a) and (b), which are steps for moving the chemical equilibrium point in the direction of desorption of the protective molecule, are as described above.

〔式中、（Ｓｉｔｅ－ＰＭ）は保護分子が吸着している金属原子の吸着サイトを示し、（Ｓｉｔｅ）は保護分子が吸着していない金属原子の吸着サイトを示し、（ＰＭ）は遊離の保護分子を示す。〕
前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程を含み、
（４）前記化学平衡の平衡点を保護分子の脱着の方向に移動させる工程が、下記（ａ’）及び／又は（ｂ’）の工程
（ａ’）前記溶媒の種類及び／又はその構成割合を変える、及び／又は、前記溶媒及び／又は基材の温度を変えることにより、下記式（ＩＩ）：
Ｋｄ＝｛［Ｓｉｔｅ］ｅｑ［ＰＭ］ｅｑ｝／［Ｓｉｔｅ－ＰＭ］ｅｑ （ＩＩ）
〔式中、［Ｓｉｔｅ］ｅｑは平衡状態における保護分子が吸着していない金属原子の吸着サイト濃度（mol/L）を示し、［ＰＭ］ｅｑは平衡状態における遊離の保護分子の濃度（mol/L）を示し、［Ｓｉｔｅ－ＰＭ］ｅｑは平衡状態における保護分子が吸着している金属原子の吸着サイト濃度（mol/L）を示す。〕
で表される保護分子の脱着平衡定数（Ｋｄ）を増大させる工程、
（ｂ’）前記溶媒に、溶媒及び／又は表面保護金属ナノ粒子を添加して、前記式（ＩＩ）における３つの濃度のうちの少なくとも１つを変化させて、前記式（Ｉ）の化学平衡が成り立たない非平衡状態とする工程、
を含むことを特徴とするものである。 Another method of forming metal on a base material in the present invention is as follows:
(1) A step of applying a dispersion containing metal nanoparticles to a substrate and bringing the substrate coated with the dispersion into contact with a solvent,
(2) the metal nanoparticles are dispersed in the dispersion in the form of surface-protected metal nanoparticles in which the surface of transition metal nanoparticles is coated with protective molecules;
(3) When the base material coated with the dispersion liquid is brought into contact with a solvent, a chemical equilibrium expressed by the following formula (I) is established between the surface-protected metal nanoparticles, metal nanoparticles, and protective molecules. established,

[In the formula, (Site-PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed, (Site) represents the adsorption site of the metal atom to which the protective molecule is not adsorbed, and (PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed. Indicates a protective molecule. ]
Shifting the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule,
(4) The step of moving the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule is the step (a') of the following (a') and/or (b'): Type of the solvent and/or its constituent ratio and/or by changing the temperature of the solvent and/or the base material, the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq (II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
A step of increasing the desorption equilibrium constant (Kd) of the protective molecule expressed by
(b') Adding a solvent and/or surface-protected metal nanoparticles to the solvent to change at least one of the three concentrations in the formula (II) to achieve chemical equilibrium of the formula (I). A process of creating a non-equilibrium state where
It is characterized by including.

In the method of forming metal on the base material (second metal forming method), metal can be formed on the surface or inside of the base material in a solvent with which the base material is brought into contact.

In the step of applying a dispersion containing metal nanoparticles to a substrate and bringing the substrate coated with the dispersion into contact with a solvent, the method of applying the dispersion containing metal nanoparticles to the substrate includes: There are no particular limitations, and examples include a method of immersing the substrate in the dispersion, a method of spray coating the substrate with the dispersion, a method of drop casting, a method of spin coating, and a method of dispensing.

When the base material is immersed in the dispersion liquid, the base material coated with the dispersion liquid may be taken out after immersion, dried, and then brought into contact with the solvent, or the base material coated with the dispersion liquid may be brought into contact with the solvent. It may be brought into contact with a solvent without drying.
When a dispersion is spray coated on a substrate, almost no dispersion medium is present on the substrate coated with the dispersion. In this case, there is no need to dry the base material coated with the dispersion liquid, and the base material can be brought into contact with the solvent as it is.

In this second metal forming method, the chemical equilibrium of the above formula (I) is established in a system in which a base material coated with a dispersion liquid is brought into contact with a solvent. The method is characterized in that the step of moving the equilibrium point of chemical equilibrium in the direction of desorption of the protective molecule includes the steps (a') and/or (b') above.
Regarding step (a') and step (b'), instead of forming metal on the base material in the dispersion liquid in step (a) and step (b) of the first metal forming method, the base material is It can be carried out in the same manner except that the metal is formed by contacting with a solvent.

Next, the dispersion of the present invention is applied to the surface of metal nanoparticles that are composed of at least one selected from the group consisting of gold, silver, copper, platinum, and palladium and have an average particle size of 1 to 30 nm.
Surface-protected metal nanoparticles coated with protective molecules containing at least one of an amino group and a carboxyl group,
It is characterized by being dispersed in a dispersion medium containing a nonpolar solvent.

As mentioned above, the average particle size of the metal nanoparticles is preferably 1 to 30 nm, more preferably 2 to 20 nm, even more preferably 2 to 10 nm, and particularly preferably 2 to 6 nm.

Here, the desorption equilibrium constant (Kd) of the protective molecule is expressed by the formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq (II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
It is expressed as
In this dispersion, when metal nanoparticles are dispersed in a dispersion medium, the desorption equilibrium constant is set to a small value from the viewpoint of adsorbing protective molecules on the surface of metal nanoparticles (positioning the equilibrium point in the direction of adsorption). It is preferably 1×10 ⁻³ (mol/L) or less, more preferably 1×10 ⁻⁴ (mol/L) or less.
On the other hand, when metal nanoparticles are liquefied, the desorption equilibrium constant is increased and the desorption equilibrium constant is 1 It is preferably 10 ^-4 (mol/L) or more, and more preferably 1×10 ^-3 or more in consideration of ease of desorption of molecules.

Further, the dispersion liquid can be used in the method for liquefying metal nanoparticles and the method for forming metal on the base material.
The various components in the dispersion are as described above.

According to the liquefaction method and metal forming method of the present invention, metal can be easily formed on the surface, or on the surface and inside of various base materials in various forms.
Further, by using the method of the present invention described above, the following advantages can be obtained.
(1) Metal nanoparticles can penetrate into the inside of the base material. As a result, the adhesion strength between the formed metal and the base material is high, the durability against repeated stretching is high, and high electrical conductivity can be obtained with a small amount of metal nanoparticles. In other words, it is possible to obtain a polymer that has both flexibility and conductivity.
(2) Metal can penetrate into nanoscale irregularities on the surface of the base material. This provides high adhesion due to the anchor effect between the base material and the metal, the base material is coated with a thin and uniform metal, and does not break even when bent.
(3) Metal nanoparticles can diffuse into nanoscale pores. Thereby, by pouring liquid metal into a mold, it is possible to easily form a metal such as a nano-implant.
(4) Metals can be supported on the base material, and when metal nanoparticles are supported in an isolated, fluidized state, the ratio of atoms occupying corners and edges on the metal surface increases, so catalytic activity can be increased with a small amount. can.

In each of the above methods of the present invention, a dispersion liquid in which surface-protected metal nanoparticles are dispersed in a dispersion medium is used. Since the surface-protected metal nanoparticles are well dispersed in the dispersion medium and the metal concentration is low, the viscosity of the dispersion is almost the same as that of the pure solvent.
Therefore, the dispersion can be applied to the substrate using a spray coating method, a dispenser method, or the like. Therefore, a conductive metal thin film can be formed not only on a smooth substrate but also on a base material having an arbitrary shape (for example, round, triangular, square, uneven, etc.). This has been difficult to achieve with conventional conductive pastes, which contain not only metal nanoparticles but also various substances to increase viscosity and form a paste.
The metal concentration in the dispersion is not particularly limited, but is preferably 0.1 to 100 mg/ml from the viewpoint of lowering the viscosity to make it easier to process and increasing the amount of metal nanoparticles that can be processed at one time. , more preferably 1 to 80 mg/ml, still more preferably 5 to 70 mg/ml.
Furthermore, when converting the metal concentration in the dispersion liquid into the metal content in the dispersion liquid, it may vary depending on the type of metal and the type of solvent used, but it is preferably 0.01 to 10% by mass, more preferably 0. .1 to 8% by weight, more preferably 0.5 to 7% by weight.

Further, patterning can be easily done by using a stencil (a type of paper pattern used in printing, etc., in which characters or patterns are cut out to allow liquid to pass through).

If dispersions of different types of transition metals constituting the metal nanoparticles are mixed and used as a dispersion of surface-protected metal nanoparticles, and the liquefaction method of the present invention is applied, an alloy can be obtained. The composition of the alloy can be adjusted to any desired ratio simply by changing the mixing ratio of the dispersion liquid.
In other words, unlike general sputtering methods and vacuum evaporation methods (methods in which a solid metal is heated in a vacuum to turn it into gaseous atoms and deposited on a substrate to form a film), the metal forming method of the present invention can be used. , it is possible to form an alloy into a film extremely easily while controlling the composition of the alloy.
In addition, although silver is often used as a wiring base material, it has the problem of electrode short-circuiting due to migration, but if we use this method to introduce palladium etc. into silver and adjust the amount introduced , migration can be prevented.

By using each of the above-mentioned methods of the present invention, metal formation can be performed in a low-temperature environment, and therefore it can be applied to polymeric base materials that do not have heat resistance (for example, low-density polyethylene, etc.).

Furthermore, if the solubility parameter of the polymer and the solubility parameter of the solvent are close, the polymer will easily absorb the solvent and swell.
Table 1 shows the solubility parameter values of various rubbers and solvents. Polydimethylsiloxane (PDMS), natural rubber, and polyurethane are typical rubber base materials (polymers). In fact, PDMS swells in hexane, natural rubber swells in cyclohexane, and polyurethane swells in methylene chloride.
Therefore, if the above-mentioned nonpolar solvent is used as a dispersion medium for a dispersion of surface-protected metal nanoparticles, when the rubber base material swells with the solvent, the metal nanoparticles will penetrate into the rubber base material. can liquefy and form metals.

Various metal base materials obtained by the above-mentioned liquefaction method and metal forming method of the present invention can be applied not only to wiring of electronic components, but also to various fields, such as stretchable electronics, wearable electronics, Flexible electronics, energy storage substrates, catalysts, mesoporous metals, etc. can be mentioned as examples of applications.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to the embodiments of these Examples.

Explanations of the abbreviations used in the examples below are as follows.
DA: Dodecylamine AuDA: Gold nanoparticles with the protective molecule dodecylamine adsorbed on the surface AgDA: Silver nanoparticles with the protective molecule dodecylamine adsorbed on the surface PdDA: Palladium with the protective molecule dodecylamine adsorbed on the surface Nanoparticle PDMS: Polydimethylsiloxane

Moreover, in the following examples, each numerical value was measured as follows.
(1) The average particle size of metal nanoparticles is determined by determining the particle size of approximately 500 metal nanoparticles by image analysis using a scanning transmission electron microscope (HD-2700, Hitachi), and calculating the number average of the particle size. Particle size.
(2) The electron microscope (TEM) used for electron microscopic observation was JEM-2100 manufactured by JEOL Ltd. The electron microscope (SEM) was JSM-7600F manufactured by JEOL.
(3) The amount of molecular adsorption is determined by measuring the weight change before and after vaporizing the protective molecules using a tube furnace (ARF-50KC manufactured by Heattech) and a micro electronic balance (BM-20 manufactured by A&D). It was measured by
(4) Electrical conductivity was measured by a four-terminal method using a source meter (2450 manufactured by Keithley).
(5) X-ray diffraction was measured using a wide-angle X-ray diffractometer (RINT2500 manufactured by Rigaku) under conditions of a voltage of 40 kV and a current of 200 mA. Note that the wavelength of the characteristic X-ray used was 1.5418 Å (CuKa ray).

(Example 1)
A dispersion liquid was prepared by dispersing AuDA in hexane. A TEM image obtained when this dispersion was applied to a Cu grid for TEM observation with a carbon support film is shown in FIG. 1(A). It can be seen that surface-protected gold nanoparticles with the protective molecule dodecylamine adsorbed on their surfaces are dispersed. Figures 1 (B), (C), and (D) show how gold nanoparticles liquefy when a Cu grid for TEM observation with a carbon support film coated with this dispersion is immersed in methanol at 30°C. Shown below. From Figure 1 (B), the protective molecule DA is desorbed from the surface of the gold nanoparticles, the gold nanoparticles liquefy, and multiple gold nanoparticles aggregate due to the flow and grow into large gold particles. I understand. 1(C) and (D) are partially enlarged views of FIG. 1(B). From FIGS. 1C and 1D, it can be seen that some of the gold nanoparticles liquefy (flow) and coalesce as part of the grown large gold particles. This phenomenon is different from the phenomenon caused by sintering, and is a characteristic of liquefaction.

(Example 2)
A dispersion liquid was prepared by dispersing AgDA in methylene chloride. Figure 2(A) shows the state after standing at 0°C for 24 hours. There was no change in the appearance of the dispersion immediately after its preparation and after it was allowed to stand at 0° C. for 24 hours. The molecular adsorption amount θ (amount of DA adsorbed on Ag nanoparticles) measured after standing at 0°C for 24 hours showed a high value of 21.3%, indicating that DA sufficiently covered the surface of Ag nanoparticles. I can see that it was. Furthermore, the electrical conductivity of AgDA film formed from the AgDA dispersion was as low as 4.1×10 ⁻⁵ S/cm, indicating that the Ag nanoparticles were coated with insulating protective molecules. At this time, it was also confirmed by electron microscopic observation and X-ray diffraction that the particle size of the Ag nanoparticles did not change at all from that immediately after the dispersion was prepared (FIG. 2(A)).
Next, the AgDA dispersion liquid left at 0°C for 24 hours was taken out from 0°C and left at room temperature (approximately 20°C), and silver precipitated on the inner wall of the glass test tube in about 1 hour ( Figure 2(B) is after standing for 2 hours). At this time, the molecular adsorption amount θ showed a very low value of 0.91%, indicating that DA was desorbed from the Ag nanoparticles. When observed with an electron microscope, it was observed that the silver nanoparticles were flowing and growing into large crystals (FIG. 2(B)). Coarsening of the silver nanoparticles was also confirmed by X-ray diffraction (FIG. 2(B)), and the silver precipitate showed a very high electrical conductivity of 3.9×10 ⁴ S/cm.
A similar phenomenon occurred even when a mixed solvent was used as a dispersion medium. AgDA was uniformly dispersed in a mixed solvent of hexane and ethanol. No change occurred even when the dispersion was allowed to stand for a long time at room temperature of 20°C, but when the temperature of the dispersion was raised to 50°C, silver precipitated on the inner wall of the test tube. In this way, even with a mixed solvent of a nonpolar solvent and a polar solvent, metal could be deposited on the surface of the substrate.

(Example 3)
Each of the AuDA-containing dispersion (dispersion medium: hexane), AgDA-containing dispersion (dispersion medium: hexane), and PdDA-containing dispersion (dispersion medium: hexane) was applied to a glass substrate by a spray coating method. When the substrate coated with AuDA and AgDA was immersed in methanol at 30°C and the substrate coated with PdDA was immersed in 2-propanol at 40°C for 1 hour (approximately 3 mg of metal nanoparticles was immersed in 20 ml of solvent), the dispersion was coated. After the substrate was immersed, the amount of protective molecules adsorbed on the metal nanoparticles (molecular adsorption amount θ) decreased (DA was desorbed from the surface of the metal nanoparticles), and the electrical conductivity increased significantly. The results are shown in Table 2.
Furthermore, when the state of the metal thin film formed on the glass substrate was observed using an electron microscope, it was observed that the metal nanoparticles had flowed and become coarse (Figures 3 (A), (B), and (C)). ).
Furthermore, the width of the diffraction peak (full width at half maximum) decreased from the X-ray diffraction pattern, and it was observed that the crystals had clearly grown significantly (in Figures 3 (A) and (B), respectively, the lower The diffraction pattern above is the sample before soaking in alcohol, and the diffraction pattern above is after soaking in alcohol).

(Example 4)
An experiment was conducted in the same manner as in Example 3, except that the substrate coated with the dispersion liquid was immersed in another alcohol. Additionally, water was used as a control. The results are shown in Table 3. Although no significant increase in electrical conductivity was observed for water (the equilibrium point is located in the direction of adsorption), the electrical conductivity increased significantly for alcohol (the equilibrium point is located in the direction of desorption).

(Example 5)
AgDA was dispersed in a mixed solution of ethanol and hexane. PDMS was immersed in the dispersion (30°C). PDMS swelled immediately, and AgDA also penetrated into the interior of PDMS (due to the small size of the metal nanoparticles, AgDA penetrated between the swollen polymer chains). The sample was left as it was for 1 hour to allow AgDA to further penetrate into the inside of the PDMS. After that, when the temperature of the dispersion liquid is raised to 50°C, the equilibrium point moves in the direction of desorption, DA is desorbed from the surface of the silver nanoparticles, the silver nanoparticles are liquefied, and silver is precipitated inside the PDMS. did.
When the same operation was repeated three times using a new AgDA dispersion solution, PDMS with a sheet resistance of about 1 ohm/sq was produced.

(Example 6)
Silver was deposited inside the polyurethane in the same manner as in Example 5, except that the polyurethane was immersed in a dispersion of AgDA in methylene chloride (FIG. 4). The left side of FIG. 4 is a photograph of the polyurethane before being immersed in the dispersion, and the right side of FIG. 4 is a photograph of the polyurethane after being immersed in the dispersion. Thereafter, the polyurethane with silver precipitated inside it was stretched, and an electric current was passed through it. The electrical conductivity was 1.1×10 ⁴ S/cm.

(Example 7)
FIG. 5 shows an SEM photograph of a rayon fiber taken out after immersing it in a dispersion of AgDA in methylene chloride. The left side of Figure 5 is an SEM photograph of the fiber cross section (top) and fiber plane (bottom) when stored at 0°C, and the right side of Figure 5 is the SEM photograph of the fiber cross section (top) and fiber plane when stored at room temperature 25°C for 1 hour. This is a SEM photograph of the plane (bottom). From FIG. 5, it can be seen that the silver in a liquid state flows into the irregularities on the surface of the rayon fibers and coats the fibers. By interlocking the irregularities on the fiber surface with the silver (anchor effect), a thin and uniform silver film was formed on the fiber surface. The electrical conductivity of the silver-coated rayon fiber was 10 ⁴ S/cm, indicating excellent electrical properties. It was also confirmed that it has high adhesiveness and durability against repeated bending, and also has high durability against repeated wetting and drying (volume change).

Claims (9)

A method for liquefying metal nanoparticles, the method comprising:
(1) The metal nanoparticles are dispersed in the dispersion in the form of surface-protected metal nanoparticles in which the surface of transition metal nanoparticles is coated with protective molecules,
The dispersion of surface-protected metal nanoparticles is produced by reducing a metal salt or metal complex in a solution in which the protective molecules are dissolved to synthesize seed crystals of metal nanoparticles, and further growing the seed crystals. is,
(2) A chemical equilibrium represented by the following formula (I) is established between the surface-protected metal nanoparticles, metal nanoparticles, and protective molecules,

[In the formula, (Site-PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed, (Site) represents the adsorption site of the metal atom to which the protective molecule is not adsorbed, and (PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed. Indicates a protective molecule. ]
Shifting the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule,
(3) the step of moving the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule ;
By changing the type and/or the composition ratio of the dispersion medium contained in the dispersion liquid, and/or by changing the temperature of the dispersion liquid, the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq(II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
A step of increasing the desorption equilibrium constant (Kd) of the protective molecule expressed by 1×10 ⁻⁴ mol/L or more and 1×10 ⁻² mol/L or less ,
A method of liquefying metal nanoparticles, comprising : A method for liquefying metal nanoparticles, the method comprising:
(1) The metal nanoparticles are dispersed in the dispersion in the form of surface-protected metal nanoparticles in which the surface of transition metal nanoparticles is coated with protective molecules,
The dispersion of surface-protected metal nanoparticles is produced by reducing a metal salt or metal complex in a solution in which the protective molecules are dissolved to synthesize seed crystals of metal nanoparticles, and further growing the seed crystals. is,
(2) comprising the step of applying the dispersion to a substrate and bringing the substrate coated with the dispersion into contact with a solvent;
(3) When the base material coated with the dispersion liquid is brought into contact with a solvent, a chemical equilibrium expressed by the following formula (I) is established between the surface-protected metal nanoparticles, metal nanoparticles, and protective molecules. established,

[In the formula, (Site-PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed, (Site) represents the adsorption site of the metal atom to which the protective molecule is not adsorbed, and (PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed. Indicates a protective molecule. ]
Shifting the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule,
(4) the step of moving the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule ;
By changing the type of the solvent and/or its constituent proportion, and/or changing the temperature of the solvent and/or the base material, the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq(II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
A step of increasing the desorption equilibrium constant (Kd) of the protective molecule expressed by 1×10 ⁻⁴ mol/L or more and 1×10 ⁻² mol/L or less ,
A method of liquefying metal nanoparticles, comprising : The method according to claim 1 or 2, wherein the metal nanoparticles have an average particle size of 1 to 30 nm. According to any one of claims 1 to 3, the transition metal constituting the transition metal nanoparticle is at least one type of element belonging to Groups 10 to 11 of the periodic table and belonging to periods 4 to 6. Method described. The method according to any one of claims 1 to 4, wherein the transition metal constituting the transition metal nanoparticles is at least one selected from the group consisting of gold, silver, copper, platinum, and palladium. The method according to any one of claims 1 to 5, wherein the protective molecule contains at least one of an amino group and a carboxyl group. A method of forming metal on a base material, the method comprising:
(1) including a step of bringing the base material into contact with a dispersion containing metal nanoparticles,
(2) the metal nanoparticles are dispersed in the dispersion in the form of surface-protected metal nanoparticles in which the surface of transition metal nanoparticles is coated with protective molecules;
The dispersion of surface-protected metal nanoparticles is produced by reducing a metal salt or metal complex in a solution in which the protective molecules are dissolved to synthesize seed crystals of metal nanoparticles, and further growing the seed crystals. is,
(3) A chemical equilibrium represented by the following formula (I) is established between the surface-protected metal nanoparticles, metal nanoparticles, and protective molecules,

[In the formula, (Site-PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed, (Site) represents the adsorption site of the metal atom to which the protective molecule is not adsorbed, and (PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed. Indicates a protective molecule. ]
Shifting the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule,
(4) the step of moving the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule ;
By changing the type and/or the composition ratio of the dispersion medium contained in the dispersion liquid, and/or by changing the temperature of the dispersion liquid, the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq(II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
A step of increasing the desorption equilibrium constant (Kd) of the protective molecule expressed by 1×10 ⁻⁴ mol/L or more and 1×10 ⁻² mol/L or less ,
A method of forming a metal on a substrate, including : A method of forming metal on a base material, the method comprising:
(1) A step of applying a dispersion containing metal nanoparticles to a substrate and bringing the substrate coated with the dispersion into contact with a solvent,
(2) the metal nanoparticles are dispersed in the dispersion in the form of surface-protected metal nanoparticles in which the surface of transition metal nanoparticles is coated with protective molecules;
The dispersion of surface-protected metal nanoparticles is produced by reducing a metal salt or metal complex in a solution in which the protective molecules are dissolved to synthesize seed crystals of metal nanoparticles, and further growing the seed crystals. is,
(3) When the base material coated with the dispersion liquid is brought into contact with a solvent, a chemical equilibrium expressed by the following formula (I) is established between the surface-protected metal nanoparticles, metal nanoparticles, and protective molecules. established,

[In the formula, (Site-PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed, (Site) represents the adsorption site of the metal atom to which the protective molecule is not adsorbed, and (PM) represents the adsorption site of the metal atom to which the protective molecule is adsorbed. Indicates a protective molecule. ]
Shifting the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule,
(4) the step of moving the equilibrium point of the chemical equilibrium in the direction of desorption of the protective molecule ;
By changing the type of the solvent and/or its constituent proportion, and/or changing the temperature of the solvent and/or the base material, the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq(II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
A step of increasing the desorption equilibrium constant (Kd) of the protective molecule expressed by 1×10 ⁻⁴ mol/L or more and 1×10 ⁻² mol/L or less ,
A method of forming a metal on a substrate, including : On the surface of metal nanoparticles made of at least one selected from the group consisting of gold, silver, copper, platinum and palladium and having an average particle size of 1 to 30 nm,
Surface-protected metal nanoparticles coated with protective molecules containing at least one of an amino group and a carboxyl group,
A dispersion liquid dispersed in a dispersion medium containing a nonpolar solvent ,
The surface-protected metal nanoparticles have the following formula (II):
Kd={[Site]eq[PM]eq}/[Site-PM]eq(II)
[In the formula, [Site]eq represents the concentration of adsorption sites of metal atoms (mol/L) on which no protective molecules are adsorbed in the equilibrium state, and [PM]eq represents the concentration of free protective molecules in the equilibrium state (mol/L). L), and [Site-PM] eq indicates the concentration (mol/L) of adsorption sites of metal atoms to which protective molecules are adsorbed in an equilibrium state. ]
The desorption equilibrium constant (Kd) of the protective molecule expressed by is 1×10 ⁻⁴ mol/L or more and 1×10 ⁻² mol/L or less,
dispersion liquid .