Preparation of conducting film composed of polyaniline and metal oxide by sol-gel method
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MATERIALS RESEARCH Preparation of conducting film composed of polyaniline and metal oxide by sol-gel method Takuya Hori, Noriyuki Kuramoto, Hideyuki Tagaya,a) Masa Karasu, Jun-ichi Kadokawa, and Koji Chiba Department of Materials Science and Engineering, Yamagata University, 4-3-16, Jonan, Yonezawa, Yamagata 992, Japan (Received 20 November 1997; accepted 19 July 1998)
Conducting thin films were prepared by entrapping water-suspended polyaniline into a silica matrix by a sol-gel route. Without metal oxide, the conductivity of the film decreased after heat treatment. However, in the presence of metal oxides such as TiO2 and Al2 O3 , the conductivity increased after heat treatment at 85 ±C and reached 17 Scm21 . The conductivity of the film depended on the kinds and amounts of metal oxides and the temperature of heat treatment.
To improve conductivity and stability of conducting polymers, entrapping them into matrices such as porous ceramics, sol-gel films, alumina, and polycarbonate have been reported.1 In the case of a silica matrix, polyacetylene, polypyrrole, polythiophene, and polyaniline have been entrapped.2,3 Polyaniline is the most promising organic conducting polymer because of its oxidative stability, and many studies have been reported on the preparation and application,4 – 8 although polyaniline is not thermally stable. In this study, we have obtained high conductivity films by entrapping polyaniline and metal oxide into a silica matrix by the sol-gel route. To entrap polyaniline into a silica matrix, watersuspended polyaniline was prepared by the polymerization of aniline in a dodecylbenzene sulfonic acid micellar system. p-Toluenesulfonic acid and 2-naphthalene sulfonic acid were less effective than dodecylbenzenesulfonic acid. Obtained colloidal sols were emerald colored.9 In a typical preparation procedure, 0.5 ml of water-suspended polyaniline was mixed with phenyltriethoxysilane (0.24 ml), ethanol (1.6 ml), and water (0.2 ml). Tetraethoxysilane, ethyltriethoxysilane, and butyltriethoxysilane were less effective precursors to obtain homogeneous and transparent silica films than phenyltriethoxysilane. 0.15 g of metal oxide was mixed when necessary and suspended before aging. The sol was stirred for 3–6 h and coated on a glass slide by using a bar coater whose clearance was 14 mm. The obtained film was aged at room temperature for 24 h. Conductivity of silica matrix which entrapped polyaniline alone was 2.9 3 1021 Scm21 . It is well known that polyaniline is thermally unstable. Actually, conductivity of polyaniline film decreased after heat a)
FIG. 1. The effects of heat treatment at 85 ±C on the conductivity of silica matrix film of polyaniline with 0.15 g of TiO2 (s) and without TiO2 (m).
Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 14, No. 1, Jan 1999
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treatment at 85 ±C as shown in Fig. 1. However, we have found that in the copresence of 0.15 g of TiO2 , the conductivity of the film increased after heat tre
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