JP2016135920A - Ferromagnetic metal nanowire - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ferromagnetic metal nanowire excellent in dispersion stability.SOLUTION: Provided is a ferromagnetic metal nanowire containing a polymer compound including a carbonate in a structure. In the ferromagnetic metal nanowire, the polymer compound is polysaccharide. Also provided is a ferromagnetic metal nanowire-dispersed liquid including the ferromagnetic metal nanowire. Also provided is a method for producing the ferromagnetic metal nanowire characterized in that ferromagnetic metal ions are reduced in a solution in the presence of a polymer compound including a carbonate in the structure in the magnetic field.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ferromagnetic metal nanowire.

  Nanowires are being studied for use in various fields as nanotechnology materials. For example, they are expected to be used for fine wiring of electronic materials, sensors, solar cells, and the like. Among nanowires, nanowires composed of ferromagnetic metals such as nickel and cobalt are attracting attention as nanomagnetic materials because they are oriented by a magnetic field.

  As nanowires exhibiting ferromagnetism, for example, Patent Document 1 discloses nickel nanowires grown from micropores in alumina after being grown in micropores in alumina and then dissolved in chromic acid / phosphoric acid solution. Has been. Patent Documents 2 and 3 disclose ferromagnetic metal nanowires in which ferromagnetic metal nanowires are grown by reducing ferromagnetic metal ions in a solution while applying a magnetic field.

JP 2012-238292 A JP 2011-58021 A International Publication No. 2014/147785 Pamphlet

  However, the nickel nanowire disclosed in Patent Document 1 is not suitable for industrial production because the production method is complicated and a large amount of alumina and chromium waste liquids are treated. In addition, nanowires are often used as a dispersion liquid from the viewpoint of handleability, but the nickel nanowires disclosed in Patent Document 1 are highly oxidized because the surface is oxidized and deteriorated by chromic acid / phosphoric acid solution treatment or the like. Dispersibility is due to charge repulsion acting between nanowires under concentration, but dispersibility under concentration suitable for wet film formation of about 0.1 to 2.0 mass% is poor, and a stable dispersion is produced There was a problem that it was difficult to do.

  When the nanowire grows, the ferromagnetic metal nanowires disclosed in Patent Documents 2 and 3 are intricately entangled and aggregated into a sheet or cotton. The agglomerated nanowires are susceptible to shearing stress and can be easily cut, so that there is a problem that the shape of the nanowires cannot be maintained even if they are fibrillated and dispersed.

  The present invention solves the above-described problems, and an object of the present invention is to provide a ferromagnetic metal nanowire excellent in dispersion stability.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that when reducing a ferromagnetic metal ion in a solution in a magnetic field, a specific compound is present in the presence of a polymer compound having a carboxylate structure. The inventors have found that the above object can be achieved by producing nanowires under solution viscosity conditions, and have reached the present invention.

That is, the gist of the present invention is as follows.
(1) A ferromagnetic metal nanowire having a polymer compound having a carboxylate structure in its surface.
(2) The ferromagnetic metal nanowire according to (1), wherein the polymer compound is a polysaccharide.
(3) The ferromagnetic metal nanowire according to (1) or (2), wherein the ferromagnetic metal is nickel.
(4) A ferromagnetic metal nanowire dispersion liquid comprising the ferromagnetic metal nanowire according to any one of (1) to (3).
(5) The ferromagnetic metal ion according to any one of (1) to (3), wherein the ferromagnetic metal ion is reduced in a solution in the presence of a polymer compound having a carboxylate structure in a magnetic field. Manufacturing method of metal nanowire.
(6) A film comprising the ferromagnetic metal nanowire according to any one of (1) to (3).
(7) The film according to (6), wherein the ferromagnetic metal nanowires are oriented in one direction.
(8) A laminate in which the film according to (6) or (7) is formed on a substrate.

According to the present invention, a ferromagnetic metal nanowire excellent in dispersion stability can be provided.
The ferromagnetic metal nanowire of the present invention can be suitably used not only for conductive films and conductive paints, but also for nanomagnetic materials, anisotropic materials, magnetic films and the like.

7 is a scanning electron microscope image of nickel nanowires obtained in Example 7. FIG. It is a transmission electron microscope image of what phosphotungstic acid dye | stained the nickel nanowire obtained in Example 7. FIG. It is the scanning electron microscope image which image | photographed the anisotropic film | membrane obtained in Example 21 from the orientation direction.

  The ferromagnetic metal nanowire of the present invention has a polymer compound layer having a carboxylate structure in its surface.

  Examples of the ferromagnetic metal constituting the nanowire include iron, cobalt, nickel, gadolinium, and alloys containing these as main components. Among these, nickel is preferable because it has high conductivity, hardly causes migration, and hardly deteriorates by oxidation.

  For example, the nanowires preferably have an average diameter of 10 to 200 nm and an average length of 1 to 100 μm. In the present invention, the average diameter is more preferably 10 to 150 nm, and the average length is more preferably 5 to 50 μm.

  The polymer compound that forms a layer on the surface of the nanowire has a carboxylate in its structure. Examples of the polymer compound having a carboxylate in the structure include carboxylmethylcellulose salt and polyacrylate. Among these, a polysaccharide having a carboxylate structure such as carboxymethylcellulose sodium salt is more preferable. The polymer compound having a carboxylate structure is water-soluble at the time of production, but once the layer is formed on the nanowire surface, it is coordinated or ionically bonded to the nanowire surface, I don't have it.

  The thickness of the polymer compound layer is preferably 1 to 10 nm. The thickness of the polymer compound layer can be confirmed by staining with phosphotungstic acid or the like and observing with a transmission electron microscope.

  The method for producing the nanowire of the present invention is not particularly limited, and examples thereof include a method in which ferromagnetic metal ions are reduced in a solution in the presence of a polymer compound having a carboxylate in the structure in a magnetic field. . When the nanowire grows by the reduction reaction, a polymer compound having a carboxylate in the structure is allowed to coexist, whereby a polymer compound film is formed on the nanowire surface.

  When reducing metal ions, the viscosity of the reaction solution is important. By controlling the viscosity of the reaction solution, nanowires can be grown longer and aggregation of nanowires can be suppressed. The viscosity of the reaction solution is preferably 50 to 1000 mPa · s, more preferably 100 to 750 mPa · s, as measured with a B-type viscometer. The solution viscosity increases by about 50 to 100 mPa · s with the progress of generation of nanowires. In the present invention, the minimum value of the solution viscosity at the start of the reaction and the maximum value of the melt viscosity at the end of the reaction are both preferably 50 to 1000 mPa · s. When the value of the solution viscosity does not satisfy the above value, nanowire growth may be suppressed.

  When reducing metal ions, the concentration of the ferromagnetic metal ions in the reaction solution is preferably 50 μmol / g or less, and more preferably 25 μmol / g or less. When the concentration of the ferromagnetic metal ion exceeds 50 μmol / g, the metal ion becomes a high concentration, and nanowire growth may be inhibited.

  The reducing agent is not particularly limited, and examples thereof include hydrazine monohydrate and hydroiodic acid. Among these, hydrazine monohydrate is preferable because it can be easily removed after the reduction reaction. The concentration of the reducing agent is not particularly limited, but is preferably 0.5 to 2.0% by mass in the solution.

  The solvent used when reducing metal ions is a solvent containing water as a main component.

  What is necessary is just to select the temperature at the time of reduce | restoring a metal ion suitably according to a reducing agent, a solvent, etc. For example, when the reducing agent is hydrazine monohydrate, the reaction is preferably performed at a temperature of 70 to 90 ° C.

  When reducing metal ions, it is preferable to add a metal having a lower ionization tendency or a metal complex thereof than the ferromagnetic metal constituting the nanowire to be generated. Metals and their metal complexes become the core of nanowire growth and promote the reduction reaction. Although it does not specifically limit as a metal seed | species used for the said metal or its complex, For example, gold | metal | money and platinum are mentioned, Among these, platinum is preferable from a viewpoint of promotion of a reduction reaction. As the metal complex, chloroplatinic acid is preferred. When platinum or a metal complex thereof is used, the concentration is preferably 0.3 μmol / g or more.

  When reducing metal ions, a complexing agent may be added to control the reduction reaction rate and the shape of the nanowires. Examples of complexing agents include citric acid, ethylenediaminetetraacetic acid, hydroxyethylethylenediaminetriacetic acid, diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid, nitrilotriacetic acid, hydroxyethyliminodiacetic acid, hydroxyiminodisuccinic acid, aminotrimethylene. Mention may be made of phosphonic acid, hydroxyethanephosphonic acid and their salts. When using a complexing agent, the concentration is preferably 0.001 μmol / g or more.

  When reducing metal ions, the pH of the solution may be adjusted to lower the reduction potential of the metal ions. By reducing the pH of the solution to 10 or more, the reduction reaction can be promoted. Examples of the alkali include sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia, butylamine, propylamine, and triethylamine. In addition, by adjusting pH, a carboxylate is formed even when carboxylic acid is added as a polymer compound.

  Although the strength of the magnetic field when reducing metal ions depends on the capacity and shape of the reaction vessel, nanowires can be suitably obtained when the magnetic flux density at the center of the vessel is about 1 mT to 10 T. The magnetic field can be applied by a superconducting magnet, an electromagnet, a neodymium magnet, or the like.

  After the reduction reaction, the nanowires can be separated and purified by filtration or the like, and then adjusted to a concentration suitable for various applications to obtain a dispersion. Although the density | concentration of the nanowire at the time of setting it as a dispersion liquid is not specifically limited, 0.1-2.0 mass% is preferable.

  The nanowire dispersion liquid of the present invention may contain a binder, a wetting agent, and a leveling agent as long as the effects of the present invention are not impaired.

  The nanowire dispersion liquid of the present invention can be applied to a substrate and dried to form a film, a laminate, a wiring or the like. Examples of the substrate include a glass substrate, a polyethylene terephthalate film, a polycarbonate film, a ceramic sheet, and a metal plate. The coating method is not particularly limited, but for example, wire bar coater coating, film applicator coating, spray coating, gravure roll coating method, screen printing method, reverse roll coating method, lip coating, air knife coating method, curtain flow coating method, dip coating Method, die coating method, spray method, letterpress printing method, intaglio printing method, and ink jet method.

  The nanowire film of the present invention may be subjected to treatment for the purpose of improving conductivity after coating. Examples of the treatment include nanowire pressure bonding treatment by heat treatment or pressing, and removal of a polymer compound by a plasma cleaner.

  When the nanowire of the present invention is used as a dispersion, there is little fusion or aggregation between nanowires, and the dispersion stability is excellent. Therefore, it can be suitably used not only for conductive films and conductive paints, but also for nanomagnetic materials, anisotropic materials, magnetic films, and the like. Moreover, since the nanowire of this invention is excellent in dispersion stability, it can be apply | coated without aggregating even in a magnetic field. Therefore, an anisotropic film in which nanowires are oriented in one direction can be formed.

  EXAMPLES Next, although an Example demonstrates this invention, this invention is not limited by these inventions.

A. Evaluation Method Evaluation methods used in Examples and Comparative Examples are as follows.

(1) Solution viscosity The solution viscosity at the start and end of the reduction reaction was measured with a B-type viscometer.

(2) Formation of nanowires The nanowires obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were collected by filtration, washed with water, dried, transferred to a carbon tape, and using a scanning electron microscope. Whether or not nanowires were formed was evaluated according to the following criteria.
○: Formation of nanowires having an average length of 10 μm or more was confirmed.
□: Formation of nanowires having an average length of less than 10 μm was confirmed.
X: Formation of nanowires could not be confirmed.

(3) State of nanowire When formation of nanowire could be confirmed, the state of nanowire in the reaction liquid after the reaction was evaluated according to the following criteria.
○: Nanowires were dispersed.
□: The nanowires were aggregated without being dispersed, but could be dispersed by stirring.
X: The nanowires were agglomerated and could not be dispersed even with stirring.

(4) Measurement of presence / absence of layer on nanowire surface and thickness thereof Nanowires obtained in Examples 7 to 20 and Comparative Examples 5 to 15 were collected by filtration, washed with water, dried and then 5% phosphotungsten. It was immersed in an acid dyeing solution for 3 minutes, and was observed with a transmission electron microscope at a magnification of 600,000 using a grid with a support film to confirm the presence or absence of a layer.
When it had a layer, 50 thickness was measured at random using the transmission electron microscope image, and the average value was calculated | required as the thickness of a high molecular compound layer.

(5) Dispersion stability of nanowire dispersion liquid The dispersion stability of the nanowire solutions obtained in Examples 7 to 20 and Comparative Examples 5 to 15 was evaluated according to the following criteria.
A: Dispersed and maintained in a dispersed state after 30 days.
○: Although it was able to be dispersed, it was aggregated after 30 days. When the aggregate was dispersed, it could be dispersed again.
□: Dispersed, but aggregated after 30 days. The agglomerates were dispersed, but could not be dispersed again.
X: It could not be dispersed.

B. Materials The materials used in Examples and Comparative Examples are as follows.
(1) Polymer compounds / BS
Daiichi Kogyo Seiyaku Co., Ltd. carboxylmethylcellulose sodium salt (low viscosity type)
・ BSH-6
Daiichi Kogyo Seiyaku Co., Ltd. carboxylmethylcellulose sodium salt (high viscosity type)
・ CAT
Polyacrylic acid 90SH manufactured by POLYSCIENCES
Hydroxypropyl methylcellulose (Metroise 90SH-100000) manufactured by Shin-Etsu Chemical Co., Ltd.
・ 500CH
Wako Pure Chemical Industries polyvinyl alcohol, polymerization degree 500, complete saponification type

Example 1
In 50 g of pure water, 0.59 g (2.48 mmol) of nickel chloride hexahydrate and 0.37 g (1.26 mmol) of trisodium citrate dihydrate were dissolved. Further, 5% aqueous sodium hydroxide solution was added dropwise to adjust the pH to 11.5, and then 1 g of BS was dissolved. After dissolution, 0.94 g (49.7 μmol) of 0.054M chloroplatinic acid aqueous solution was added, and then water was added to a total amount of 75 g to prepare a nickel ion solution.
On the other hand, 40 mg of 5% sodium hydroxide and 1.25 g of hydrazine monohydrate were added to 20 g of pure water to prepare a reducing agent solution.
Both the nickel ion solution and the reducing agent solution were heated to 80 to 85 ° C., then mixed while maintaining the temperature, a 1 T magnetic field was applied, a reduction reaction was performed for 1 hour, and nickel nanowires were produced.

Examples 2 and 3
As shown in Table 1, the same operation as in Example 1 was performed except that the polymer compound used was changed, and nanowires were produced.

Examples 4-6
As shown in Table 1, the same operation as in Example 1 was performed except that the addition amount of BS was changed, and nanowires were produced.

Comparative Example 1
In 50 g of pure water, 0.59 g (2.48 mmol) of nickel chloride hexahydrate and 0.37 g (1.26 mmol) of trisodium citrate dihydrate were dissolved. Furthermore, after 5% sodium hydroxide aqueous solution was added dropwise to adjust to 11.5, 0.054M chloroplatinic acid aqueous solution 0.93g (49.7μmol) was added, and then water was added so that the total amount became 75g. Then, a nickel ion solution was prepared.
On the other hand, 0.04 g of 5% sodium hydroxide and 1.25 g of hydrazine monohydrate were added to 20 g of pure water to prepare a reducing agent solution.
Both the nickel ion solution and the reducing agent solution were heated to 80 to 85 ° C., then mixed while maintaining the temperature, a 1 T magnetic field was applied, a reduction reaction was performed for 1 hour, and nickel nanowires were produced.

Comparative Examples 2 and 3
As shown in Table 1, except that BS was changed to a polymer compound not having a carboxylate structure, an attempt was made to produce a nanowire by performing the same operation as in Example 1, but the nanowire was formed. I couldn't.

Comparative Example 4
As shown in Table 1, except that the concentration of BS was changed, the same operation as in Example 1 was performed to produce a nanowire, but the nanowire could not be formed.

Example 7
After the nanowire obtained in Example 1 was collected by filtration and washed with water, water was added so that the concentration of the nanowire was 0.5% by mass to prepare a nanowire dispersion.

Example 8
After the nanowire obtained in Example 1 was collected by filtration and washed with water, BS and water were added so that the nanowire concentration was 0.5 mass% and the BS concentration was 0.1 mass%. A nanowire dispersion was prepared.

Examples 9, 10, 12-20
Except changing the kind and density | concentration of nanowire to be used like Table 2, operation similar to Example 7 was performed and the nanowire dispersion liquid was produced.

Example 11
Except changing the kind and density | concentration of nanowire to be used, and the density | concentration and kind of additive as Table 2, operation similar to Example 8 was performed and the nanowire dispersion liquid was produced.

Comparative Examples 5 and 12
Except changing the kind and density | concentration of nanowire to be used like Table 2, it tried to produce a nanowire dispersion liquid by performing operation similar to Example 7, but nanowire could not be disperse | distributed.

Comparative Examples 6-11, 13
Except for changing the type and concentration of the nanowire used and the concentration and type of the additive as shown in Table 2, an attempt was made to produce a nanowire dispersion by performing the same operation as in Example 8, but the nanowire was dispersed. I couldn't.

Comparative Example 14
The nanowire obtained in Example 1 was baked at 600 ° C. for 2 hours in an oxygen atmosphere to remove the surface polymer compound layer. Although water was added to the nanowires after firing so that the concentration of the nanowires was 0.5% by mass to prepare a nanowire dispersion liquid, the nanowires could not be dispersed.

Comparative Example 15
Using nanowires baked in the same manner as in Comparative Example 14, BS and water were added so that the nanowire concentration was 0.5 mass% and the BS concentration was 0.1 mass%, I tried to make it, but I couldn't disperse the nanowires.

Example 21
After the nanowire obtained in Example 1 was recovered by filtration and washed with water, BSH-6 was adjusted so that the concentration of nanowire was 0.5 mass% and the concentration of BSH-6 was 0.5 mass%. Water was added to prepare a nanowire dispersion.
The obtained nanowire dispersion liquid was applied onto a glass substrate with an applicator, and the glass substrate was left standing and dried in a magnetic circuit having a central magnetic field of 150 mT to form a nanowire film on the substrate. The body was made.
Electrodes were attached to both ends in one direction of the nanowire film on the obtained laminate, and the resistance between the electrodes was measured with a tester. The resistance value was 1.8 × 10 ¹⁴ Ω.
On the other hand, the same operation as described above was performed to prepare a laminate in which a nanowire film was formed on a substrate, and then the nanowire film was peeled off, electrodes were attached to both surfaces of the nanowire film with a conductive paste, When the resistance was measured with a tester, the resistance value was 2.9 × 10 ⁻² Ω.

Example 22
In the same manner as in Example 21, a nanowire film was produced on a glass substrate. Made

Tables 1 and 2 show the manufacturing conditions of the nanowires of Examples 1 to 6 and Comparative Examples 1 to 4 and the evaluation results of the dispersions prepared using the nanowires.

Since the nanowires of Examples 1 to 6 had a polymer compound layer having a carboxylate structure on the surface, the nanowires were excellent in dispersion stability as in Examples 7 to 20.
Since the nanowires of Examples 1 and 2 were prepared using a polysaccharide having a carboxylate salt structure, the nanowires were more excellent in dispersion stability than the nanowires of Example 3.

  Moreover, since the nanowire of Example 1 was excellent in dispersion stability, as in Example 21, an anisotropic film in which nanowires were oriented in one direction without being aggregated even in a magnetic field was used. Could be formed.

  The nanowire of Comparative Example 1 is prepared without using a polymer compound having a carboxylate in its structure. Therefore, the nanowire of Comparative Example 1 did not have a polymer compound layer on the surface, and the dispersion stability was poor as in Comparative Examples 5 to 13.

Claims (8)

A ferromagnetic metal nanowire having a polymer compound having a carboxylate structure in its surface. 2. The ferromagnetic metal nanowire according to claim 1, wherein the polymer compound is a polysaccharide. The ferromagnetic metal nanowire according to claim 1 or 2, wherein the ferromagnetic metal is nickel. A ferromagnetic metal nanowire dispersion liquid comprising the ferromagnetic metal nanowire according to claim 1. The production of a ferromagnetic metal nanowire according to any one of claims 1 to 3, wherein the ferromagnetic metal ion is reduced in a solution in the presence of a polymer compound having a carboxylate structure in a magnetic field. Method. A film comprising the ferromagnetic metal nanowire according to claim 1. The film according to claim 6, wherein the ferromagnetic metal nanowires are oriented in one direction. A laminate, wherein the film according to claim 6 or 7 is formed on a substrate.