JP2000086760A - Formation of conductive polymer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyaniline film having a good film quality. SOLUTION: This method for forming a conductive polymer film comprises forming a conductive polymer (polyaniline) on a conductive substrate as an electrode by an electrochemical polymerization method, while applying a centrifugal field.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming a conductive polymer film by an electrolytic oxidation polymerization method.

[0002]

2. Description of the Related Art Conventionally, organic polymer materials are mainly coated,
It has been used for passive applications such as protection and electrical insulation.In recent years, however, a great deal of research and development has led to the synthesis of polymers that have excellent electrical and optical properties one after another. There is a growing trend to apply it to active applications.

[0003] Among them, conductive polymers have been found to have properties comparable to metallic conductivity, and their use as electrode materials and electrolytes in batteries, capacitors, chemical sensors and the like has been studied. Furthermore, in addition to having electrical characteristics equal to or higher than that of a metal material, workability, light weight, and low cost have attracted attention, and some have reached the level of practical use.

Among the conductive polymers, polypyrrole, polyaniline, polythiophene, and polyphenol have been intensively researched and developed, elucidating the structure and reaction mechanism, optimizing the synthesis conditions, electrical, chemical, and optical characteristics. Have been reported, and various electronic and chemical devices to which these have been applied have been proposed.

[0005] Among them, polyaniline has been attracting attention for a long time because of its high conductivity, stable environmental resistance, and small change with time.

As a method for producing polyaniline, for example, as described in JP-A-6-200017, a method in which aniline is chemically oxidized and polymerized with an oxidizing agent,
Journal of Electroanalytical Chemistry,
As described in Vol. 111, pp. 111-114, 1980, a method of electrochemical oxidative polymerization (hereinafter referred to as electrolytic oxidative polymerization) is generally used.

[0007] Synthetic Metals
ls), vol. 41-43, p. 715, 1991, it has been elucidated that polyaniline has three oxidation states, and high conductivity appears depending on the oxidation state. It is shown. Therefore, when polyaniline is formed as a solid electrolyte by ordinary chemical polymerization, if the oxidation is insufficient or if it is overoxidized, its high conductivity may not be able to be used to its full potential. It has been pointed out that it is difficult to achieve this.

Further, as for a method of forming a conductive polymer film on a desired base material, as described in JP-A-6-310380, a method of directly synthesizing and forming a film on an aluminum oxide film is known. And JP-A-3-355
As described in Japanese Patent Publication No. 16, a method of synthesizing polyaniline once by a chemical polymerization method, dissolving the polyaniline in an organic solvent to prepare a solution, and then forming a film by a casting method or a dipping method is widely known. ing.

However, as described in JP-A-3-35516, polyaniline polymerized by chemical polymerization is hardly soluble in an organic solvent, so that it is very difficult to prepare a high-concentration solution. It has been pointed out that the molecular structure must be controlled in order to make it soluble.

On the other hand, in the electrolytic oxidation polymerization method, the reaction control is easier and the synthesis time can be shortened as compared with the chemical oxidation polymerization method. If the substrate is electrically conductive, it can be formed directly on the substrate, and thus has been widely studied. However, Electrochemistry, Vol. 65, No. 6, p. 495, 1997.
In 1980, the problem that the film quality of polyaniline formed by the electrolytic oxidation polymerization method was coarse and the density was low was described.

[0011]

As described above, since the polyaniline film formed by the conventional oxidative polymerization method has a rough film quality, the original electrical characteristics, chemical characteristics and mechanical characteristics of polyaniline can be obtained. It is thought that there is no.

An object of the present invention is to provide a polyaniline film having good film quality.

[0013]

This object is achieved by one of the following (1) and (2). (1) A method for forming a conductive polymer film, wherein a conductive polymer is formed on the substrate by electrochemical polymerization while applying a centrifugal field using the conductive substrate as an electrode. (2) The method for forming a conductive polymer film according to the above (1), wherein the conductive polymer is polyaniline.

[0014]

In the present invention, a film made of a conductive polymer, polyaniline, is formed by electrolytic oxidation polymerization while applying a centrifugal field. The film quality of the polyaniline film thus formed becomes dense. For this reason, conductivity becomes high, and not only electrochemical characteristics but also environmental resistance and mechanical characteristics are improved. Therefore, the polyaniline film formed according to the present invention can be applied to various uses by utilizing the inherent characteristics of polyaniline.

FIG. 1 shows a configuration example of an apparatus used for electrolytic oxidation polymerization under a centrifugal field. This apparatus uses a general centrifuge, and an electrolysis cell 3 is arranged in one of a pair of centrifuge tubes 2. The details of the electrolytic cell 3 are shown in FIG. A pair of electrodes A and B and a reference electrode (silver-silver chloride wire) 4 are arranged in the electrolytic cell 3, and the electrodes A and B are connected to an external DC power supply via a rotating shaft 5. Connected. In FIG. 2, the electrode A whose surface is vertically upward with respect to the centrifugal force is referred to as an electrode arranged in the reverse direction (or reverse electrode) in this specification, and the surface is vertically downward with respect to the centrifugal force direction. The electrode B is referred to as a forward electrode (or a forward electrode) in this specification. Therefore,
In the electrolytic oxidation polymerization under a centrifugal field, when the reverse electrode A is used as the working electrode, the centrifugal force is opposite to the direction in which the conductive polymer film grows by polymerization, and the forward electrode B is used as the working electrode. In that case, the centrifugal force is in the same direction.

In electrolytic oxidation polymerization under a centrifugal field, there is a remarkable difference in the film quality of the polyaniline film formed between the case where the reverse electrode A is used as the working electrode and the case where the forward electrode B is used as the working electrode. Can be

In the reverse electrode A, the polymerization reaction speed increases as the centrifugal force increases, while in the forward electrode B, the polymerization reaction speed decreases. In the initial stage of polymerization, oligomers with a low degree of polymerization are generated, which are separated from the electrode interface,
The mechanism of re-dissolving in the electrolyte works. Reverse electrode A
Then, this mechanism is suppressed by the action of centrifugal force,
On the other hand, since it is not suppressed by the forward electrode B, it is considered that a difference appears in the polymerization reaction rate as described above. This is supported by the fact that, when the forward electrode B is used as the working electrode, the amount of oligomer increases in the UV absorption spectrum of the electrolytic solution after electrolysis.

The properties of the polyaniline film are very fine microscopically composed of fine aggregated particles at the reverse electrode A, while those of the relatively large and substantially spherical aggregated particles are at the forward electrode B. Macroscopically dense, and all are in a very stable state. Then, the adhesion to the electrode as the base material is extremely good in any case.

The Abstracts of the 64th Annual Meeting of the Electrochemical Society of Japan, 3D28, 121, and the Abstracts, 3D29, 1
As described on page 22, preliminary studies on electrode reactions related to metal deposition and corrosion in a centrifugal field have been reported, but the use of a centrifugal field for the synthesis of organic compounds, especially for the synthesis of conductive polymers, has been reported. There have been no reports on the use of this technology.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The anode substrate (electrode on which a polyaniline film is formed) used in the present invention is not particularly limited, but is made of a conductive material which does not exhibit an obstructive behavior to the electrolytic oxidation polymerization reaction to be carried out. Is appropriate. Specifically, platinum, gold, silver, titanium, niobium, tantalum, stainless steel, nickel, aluminum, zirconium, carbon, or the like, or an alloy thereof can be used. The shape of the electrode is not particularly limited, and may be appropriately determined so as to make use of the effect of the centrifugal field.
Any of a plate-like or porous block may be used. In addition, lamination and winding may be performed as necessary.

The electrolytic oxidation polymerization itself may be performed according to a known method. That is, electrolytic oxidation polymerization is carried out by placing the anode substrate as a working electrode, placing it in an electrolytic solution together with a counter electrode, and applying a current.

The electrolytic solution contains a raw material monomer of polyaniline, a supporting electrolyte, a compound that provides a dopant species to be added as needed, and various additives as needed.

The starting monomers include, for example, unsubstituted anilines, alkylanilines, alkoxyanilines,
Haloanilines, o-phenylenediamines, 2,6-
Examples thereof include dialkylanilines and 2,5-dialkoxyanilines.

The compound that provides the supporting electrolyte or the dopant species is not particularly limited, and examples thereof include the following compounds.

The anion is a hexafluorophosphoric anion,
A hexafluoro arsenic anions, salt cation is an alkali metal cation of lithium, sodium, and potassium, for example, LiPF _6, LiAsF _6, NaPF
₆ , KPF ₆ , KAsF ₆ and the like. In addition to these, boron tetrafluoride compounds such as LiBF ₄ , NaB
_{F 4, NH 4 BF 4,} (CH 3) 4 NBF 4, (n-C 4 H 9)
₄ NBF ₄ and the like. Further, a sulfonic acid or a derivative thereof, for example, p-toluenesulfonic acid, p-ethylbenzenesulfonic acid, p-hydroxybenzenesulfonic acid, dodecylbenzenesulfonic acid, methylsulfonic acid,
Dodecylsulfonic acid, benzenesulfonic acid, β-naphthalenesulfonic acid and salts thereof, for example, sodium 2,6-naphthalenedisulfonic acid, sodium toluenesulfonic acid, tetrabutylammonium toluenesulfonic acid and the like.

Metal halide compounds such as ferric chloride, ferric bromide, cupric chloride and cupric bromide.

A hydrohalic acid, an inorganic acid or a salt thereof,
For example, hydrochloric acid, hydrogen bromide, hydrogen iodide, sulfuric acid, phosphoric acid,
Nitric acid, or an alkali metal salt, an alkaline earth metal salt or an ammonium salt thereof, a perhalic acid such as perchloric acid or sodium perchlorate, or a salt thereof.

Carboxylic acids such as acetic acid, oxalic acid,
Mono- or dicarboxylic acids such as formic acid, butyric acid, succinic acid, lactic acid, citric acid, phthalic acid, maleic acid, benzoic acid, salicylic acid, nicotinic acid, aromatic and heterocyclic carboxylic acids, and halogenated compounds such as trifluoroacetic acid Carboxylic acids and salts thereof.

These compounds are used as a solution, that is, in a state of being dissolved in water or an organic solvent. The solvents may be used alone or as a mixture of two or more. The mixed solvent is also effective for increasing the solubility of the compound giving the dopant species. Examples of the mixed solvent include those having compatibility between the solvents and those having compatibility with the compound. The dissolution concentration may be set so as to obtain a desired current density, and generally there is no particular problem if the concentration is in the range of 0.005 mol / l to 1.0 mol / l.

The solvent used in the electrolytic oxidation polymerization is not particularly limited, and may be appropriately selected from, for example, water, a protic solvent, an aprotic solvent, or a mixed solvent obtained by mixing two or more of these solvents. As the mixed solvent, those having compatibility between the solvents and those having compatibility with the monomer and the supporting electrolyte are suitable.

Examples of the protic solvent include formic acid, acetic acid, propionic acid, methanol, ethanol, n-propanol, isopropanol, tert-butyl alcohol, methyl cellosolve, diethylamine and ethylenediamine. Examples of aprotic solvents include methylene chloride, 1,2-dichloroethane, carbon disulfide, acetonitrile, acetone, propylene carbonate, nitromethane, nitrobenzene, ethyl acetate, diethyl ether,
Tetrahydrofuran, dimethoxyethane, dioxane,
N, N-dimethylacetamide, N, N-dimethylformamide, pyridine, dimethylsulfoxide and the like can be exemplified.

For the electrolysis, any of the constant voltage method, the constant current method and the potential sweeping method may be used. Further, a method in which the constant current method and the constant voltage method are combined in the electrolytic polymerization process can also be used. The current density is not particularly limited, but is about 10 mA / cm ² at the maximum. The thickness of the polyaniline film can be arbitrarily selected by the electrolysis time in the constant voltage method and the constant current method, and can be arbitrarily selected by the number of potential sweeps in the potential sweep method.

The electrolysis is performed while applying a centrifugal field as described above. The centrifuge is a relatively small process.
It can be generated by a general centrifuge as shown in FIG. On the other hand, in the case of a medium- or large-scale process, it can be generated using an annular or cylindrical centrifuge (one that has been put into practical use for isotope separation or the like). The constituent material of the electrolytic cell is not particularly limited, and may be, for example, any of glass, plastic, metal, and the like. The direction of the working electrode in the electrolytic cell may be appropriately set according to the required film quality, uniformity of the molecular structure, and the like.

The centrifugal acceleration is 10 g (g is the gravitational acceleration)
It is preferable that it is above. If the centrifugal acceleration is too small, a sufficient effect cannot be obtained.

The temperature of the electrolytic bath may be between the freezing point and the boiling point of the electrolytic solution, but is usually about 0 to 60 ° C.

After the electrolytic oxidation polymerization, the working electrode is taken out of the electrolytic cell, washed with an appropriate solvent, and dried.

[0037]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

The electrolytic cell shown in FIG. 2 was set in a centrifuge, and the electrolytic device shown in FIG. 1 was produced. Note that a cylindrical cell made of an acrylic resin was used for the electrolytic cell, and a platinum disk was used for each of the reverse electrode A and the forward electrode B. The aniline monomer was 0.1 mol /
l, hydrochloric acid containing 4.0 mol / l.

Using this electrolysis apparatus, 0 to 1.0 V vs.
Silver / silver chloride electrode, potential sweep electrolysis was repeated 50 times at a sweep speed of 100 mV / s, reverse electrode A or forward electrode B
Was used as a working electrode to form a polyaniline film thereon. During electrolysis, an acceleration in the range of 1 to 350 g was applied.
Note that the acceleration of 1 g is a state in which no centrifugal force is applied (only gravitational acceleration).

Polymerization Rate The effect of the centrifugal field on the current value of the first oxidation peak of the polyaniline film in this electrolysis is shown in FIG. Reverse electrode A
When the working electrode is used as the working electrode, the current value serving as an index of the amount of polymerization increases as the centrifugal acceleration increases, and it can be seen that the polymerization rate increases. On the other hand, when the forward electrode B was used as the working electrode, the current value decreased with an increase in the centrifugal acceleration, indicating that the polymerization rate was suppressed. From this result, it is clear that the effect of the centrifugal field on the electrolytic oxidation polymerization reaction is anisotropic and depends on the direction of the working electrode.

The film quality cleaning, the surface state of the polyaniline film after drying was examined by scanning electron microscope (SEM). As a result, it was found that, with the reverse electrode A, the lumped particles constituting the film qualitatively became finer as the centrifugal acceleration increased, and were significantly densified. On the other hand, in the forward electrode B, it was found that the massive particles were substantially spherical and dense but coarser than those in the reverse direction. FIG. 4 shows an SEM photograph of the film formed on the reverse electrode A without applying centrifugal force.
SE of membrane formed on reverse electrode A under centrifugal force of 15 g
FIG. 5 shows an M photograph, and FIG. 6 shows an SEM photograph of the film formed on the forward electrode B under the centrifugal force of 288 g.

UV Absorption Spectra The electrolytic solution used to form the above three types of polyaniline films whose film quality was observed by SEM was measured for UV absorption spectra after electrolysis. FIG. 7 shows the results. FIG. 7 also shows a UV absorption spectrum before electrolysis. From FIG. 7, it can be seen that the electrolytic solution used for forming the polyaniline film on the forward electrode B under the centrifugal field has an absorption peak at a wavelength of about 330 nm due to the aniline oligomer.

The polyaniline film formed on the reverse electrode A under a centrifugal acceleration of 50 to 300 g was washed and dried, and then subjected to a peeling test using an adhesive tape. As a result, almost no polyaniline was attached to the adhesive tape side, and polyaniline remained on the reverse electrode A side. From this result, it is understood that the adhesion of the polyaniline film to the electrode is remarkably good.

On the other hand, in the polyaniline film formed without applying the centrifugal force, most of the polyaniline adhered to the adhesive tape side in the peeling test, and almost no polyaniline remained on the electrode side.

The effects of the present invention are clear from the results of the above examples.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an experimental apparatus for performing electrolytic oxidation polymerization in a centrifugal field.

FIG. 2 is a front view showing a structure of an electrolytic cell in the experimental apparatus of FIG.

FIG. 3 is a graph showing the relationship between acceleration and current value during electrolytic oxidation polymerization in a centrifugal field.

FIG. 4 is a drawing substitute photograph showing a particle structure, which is a scanning electron microscope photograph of a polyaniline film.

FIG. 5 is a drawing substitute photograph showing a particle structure, which is a scanning electron microscope photograph of a polyaniline film.

FIG. 6 is a drawing substitute photograph showing a particle structure, which is a scanning electron microscope photograph of a polyaniline film.

FIG. 7 is a graph showing a UV absorption spectrum of a polyaniline film.

[Explanation of symbols]

 2 Centrifuge tube 3 Electrolysis cell 4 Reference electrode 5 Rotation axis A, B electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Ryoichi Aoki, 2-20-12-1304 Ryogoku, Sumida-ku, Tokyo (72) Masaaki Kobayashi, 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation ( 72) Inventor Noriyoshi Nanba 1-13-1, Nihonbashi, Chuo-ku, Tokyo F-term in TDK Corporation 4J043 PA02 QB02 RA08 SA05 SB01 UA121 XA21 YB12 YB13 YB15 YB17 YB38 ZA44

Claims (2)

[Claims] 1. A method for forming a conductive polymer film, comprising forming a conductive polymer on a substrate by electrochemical polymerization while applying a centrifugal field using the substrate having conductivity as an electrode. 2. The method according to claim 1, wherein the conductive polymer is polyaniline.