Conducting Molecular Multilayers: Intercalation of Conjugated Polymers in Layered Media
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CONDUCTING MOLECULAR MULTILAYERS: INTERCALATION OF CONJUGATED POLYMERS IN LAYERED MEDIA V. MEHROTRA AND E.P. GIANNELIS Department of Materials Science and Engineering, Ithaca, NY 14853.
Cornell University,
ABSTRACT Polyaniline has been synthesized in the galleries of fluorohectorite, a two-dimensional mica-type layered silicate. Intercalation of aniline in the intracrystalline region of Cu-exchanged fluorohectorite results in oxidative polymerization to polyaniline (emeraldine base form) as demonstrated by electronic, infrared and Raman spectroscopy and x-ray diffraction data. The intercalated insulating form of polyaniline becomes conducting on exposure to HCI. In-plane electrical conductivity data measured in the temperature range 274 to 573 K show a complex thermally activated behavior with room temperature conductivity 0.05 Ohm-Icm"I. The polyaniline/layered silicate hybrids represent a new class of nanocomposites consisting of synthetic conductors with molecular dimensions contained in a quasi twodimensional environment of a crystalline host.
INTRODUCTION Research on electrically conducting polymers has recently focused on the synthesis and characterization of environmentally robust materials with high degree of processability and high conductivity [1]. An intriguing new challenge in the area of conducting polymers is to isolate or confine them in a well defined environment. Such systems would not only provide fundamental information on the electronic structure and the conduction mechanism but they could also represent a new class of hybrid composites with nanometer dimensions. The properties of these new materials can be tailored
by
inserting
suitable
guest
molecules
into
the
well
defined
galleries of the host lattice. Previous work in this area includes intercalation of polypyrrole and polythiophene in layered FeOCl [2], intercalation of aniline in V2 0 5 [3], and encapsulation of chains of aniline, pyrrole and thiophene in zeolites
[4,5]. Formation of conjugated polymers in the galleries of mica-type silicates was first observed almost twenty years ago by Pinnavaia and Mortland by a unique charge-transfer reaction [6]. Certain aromatic molecules can be incorporated into the galleries of layered silicates whose exchangeable cations have been replaced by transition metal ions like Cu, Ru, etc., and form charge-transfer complexes. For example in the case of benzene, intercalation leads to the formation of poly-p-phenylene under exhaustively dry conditions. Previous studies focused mainly on spectroscopic studies offering no information on their electronic properties or conduction mechanism [7,8]. In addition, intercalation of aniline in layered silicates has not been studied. Polyaniline (PANI) is a novel conducting polymer, that in contrast to other conducting polymers its electronic properties can be switched from insulating to conducting by electrochemical oxidation and/or chemical protonation.
Mat. Res. Soc. Symp. Proc. Vol. 171. ©1990 Materials Research Society
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synthesis of in situ We
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