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Investigation of the electrical properties of polymer–clay nanocomposites is important in the development of nanoelectronic devices. These nanocomposites may be prepared by intercalating suitable monomers within interlayer spaces of expanding layered clay materials, followed by in situ polymerization. We made use of this approach to prepare montmorillonite–polyaniline nanocomposites by ion-exchanging the intergallery cations for anilinium ions and subsequently polymerizing the anilinium ions by peroxydisulphate in the acidic medium to yield emeraldine salt form of polyaniline intercalated in montmorillonite (ES1-MMT). The emeraldine salt form of polyaniline contains one positive charge per three monomer units, and hence, polymerization of anilinium ions reduces the number of cations present within the interlayer. Charge compensation thus requires uptake of required amount of cations from the solution. Further, the emeraldine salt form of polyaniline can be neutralized by treating with excess base such as ammonia. Thus, the neutralization of emeraldine salt results in an uptake of ammonium ions for charge balance. We have, therefore, neutralized ES1-MMT using aqueous ammonium hydroxide, and the cations inserted into the interlayer were again exchanged for anilinium ions. The latter was polymerized in acidic medium to yield more polyaniline in its emeraldine salt form (ES2-MMT). By repeating this procedure we have also prepared ES3-MMT. X-ray diffraction (XRD) spectra recorded at 150 °C reveal the enhancement of d-spacing upon increased amounts of polymer formation, and the Fourier transform infrared (FTIR) analysis also supports this by showing enhanced absorption due to bands typical of emeraldine salt (for example, B–NH+ = Q, where B and Q stand for benzanoid and quinoid, respectively). Careful analyses of FTIR spectra reveal that the polymer is present within the interlayers, as well as adsorbed onto the external surfaces and is bound to clay layers through hydrogen bonding. In this publication, we report the electrical properties of such ES-MMT nanocomposites. Alternating current (AC) impedance analysis shows that the nanocomposites are highly conducting materials, and their bulk conductivity enhances in the order ES1-MMT < ES2-MMT < ES3-MMT. The materials are pure electronic conductors as revealed by the direct current polarization studies. Further, their conductivities decrease with increasing temperature as of pure electronic conductors. By treating kaolinite with anilinium ions in acidic medium followed by peroxydisulphate ions, emeraldine salt–kaolinite (ES-KAL) composites have also been prepared. Because kaolinite is a non-expanding clay, the ion exchange is not possible, and hence, the polymer cannot be incorporated into the interlayer. This is indeed shown in the XRD analysis. The polymer can only reside out of the kaolinite particles. FTIR spectra reveal the hydrogen bonding between the polymer and kaolinite outer surfaces. AC impedance spectra of ES-KAL do not show high bulk conductivity. Thus, the comparison of AC impedance spectra of ES-KAL with ES-MMT systems clearly indicates that the bulk conductivity of the latter systems is predominantly due to intercalated polyaniline.

This paper describes the preparation and characterization of conducting polyaniline-montmorillonite (PANI-MMT) nanocomposites by the polymerization of anilinium ions within the interlayer space of MMT particles. A procedure for the successive introduction of PANI chains within the interlayer galleries of MMT is developed. The d-spacing, measured after heat treatment at various temperatures serves as a measure of the amount of polymer inserted in the clay intergalleries. The FTIR spectroscopy reveals the presence of host-guest interactions of a hydrogen-bonded nature. The DC conductivities were found to increase with the amount of PANI intercalated. Anilinium ions supported on kaolinite tended to dislodge from the surface upon repeated washings, as shown by the absence of polymer formation on such samples upon treatment with the oxidant. In MMT, however, polymerization is observed even with exhaustively washed samples, thus confirming that the successive polymerization processes occur within the interlayer galleries. Exclusion of the washing stage gives a composite material in which polyaniline is present on both the internal and external surfaces. This material is found to have significantly higher electronic conductivities than the composites where the polymer is restricted to interlayer galleries. The washed samples of the polymer once loaded into the clay (EMS1-MMT), twice loaded into the clay (EMS2-MMT) and thrice loaded into the clay (EMS3-MMT) have electrical conductivities of 4.5 × 10−5, 3.0 × 10−4, and 1.0 × 10−3 Scm−1, respectively in their dry states. The corresponding samples prepared by excluding the washing procedure had the values of 4.0 × 10−4, 1.0 × 10−2, and 1.0 10−1 Scm−1, respectively.

TRANSITION metal, ion-exchanged montmorillonites form complexes1,2, often of an interlamellar kind (intercalates), with a range of aromatic molecules, including benzene, toluene and the xylenes, anisole, and other species such as trans-stilbene and indene3–5. The aromatic molecules can form two main types of complex with the interlayer transition-metal ions, for example Cu(II). In the first type there is thought to be an edge-π-bonded copper arene moiety, similar to the bonding situation which exists in C6H6CuAlCl4 (ref. 6), and in the second instance it is considered to be a type of bond which causes associated distortion of the aromatic ring and some localisation of the circumferential double bonds1. Although detailed crystallographic analyses of the organic intercalates of sheet silicates has only recently commenced (ref. 7, and J. M. Adams et al., unpublished) and in spite of the paucity of information relating to the precise nature of the bonding of organic entities to encaged metal ions, it is clear2–4 that these organic complexes display a rich range of unusual reactions, some new examples of which we report here.

TRANSITION metal, ion-exchanged montmorillonites form complexes1,2, often of an interlamellar kind (intercalates), with a range of aromatic molecules, including benzene, toluene and the xylenes, anisole, and other species such as trans-stilbene and indene3–5. The aromatic molecules can form two main types of complex with the interlayer transition-metal ions, for example Cu(II). In the first type there is thought to be an edge-π-bonded copper arene moiety, similar to the bonding situation which exists in C6H6CuAlCl4 (ref. 6), and in the second instance it is considered to be a type of bond which causes associated distortion of the aromatic ring and some localisation of the circumferential double bonds1. Although detailed crystallographic analyses of the organic intercalates of sheet silicates has only recently commenced (ref. 7, and J. M. Adams et al., unpublished) and in spite of the paucity of information relating to the precise nature of the bonding of organic entities to encaged metal ions, it is clear2–4 that these organic complexes display a rich range of unusual reactions, some new examples of which we report here.