1. Phys. Chem. SoM Vol. 54, No. I I, PP. 16134620, 1993 Printed in Great Britain. 0022-X91/93 S6.M) + 0.00 0 1993 Pergamon Prns Ltd ABSORPTION INDUCED RESPONSE OF ELECTROPHYSICAL CHARACTERISTICS OF FILLED POLYMER-COMPOSITE D. Yu. GODOVSKI,~ V. YA. SUKHAREV,# A. V. VOLKOV§ and M. A. MOSKWNA§ tKurchatov Atomic Energy Institute, 123182, Moscow, Russia IL. Ya. Karpov Institute of Physical Chemistry, Moscow 103064, Obucha St., 10, Russia $Chemical Department of Moscow State Univ., Moscow, Leninsky Pr., 21, Russia (Received 2 October 1992; accepted in revised form 15 April 1993) Abstract-The synthesis and investigation of polymer-composite films prepared on the basis of hy- drophilous polymer matrix (polyvinylalcohol (PVA)) filled with the copper sulfide (CuS) semiconductor particles of nanosixe (SO-200 A) are described in the present paper. It was found that in the concentration range from 16 to 22% given systems undergo the percolation threshold, accompanied by a conductivity change from 1O-9 to 10v2 (ohmcm-‘. Magnetoresistance behavior for samples with CuS concentrations both just before and in the area of percolation, along with the form of conductivity-temperature and conductivity-composition dependen- cies in given concentrations range provides the evidence for hopping mechanism of conductivity in that area of filler concentrations. Conductivity response caused by water vapor absorption for compositions with the concentrations of tiller closed to scaling area (1622%) is considered in terms of models, proposed for hopping conductivity of isle-like films. We suggest here that the dominant role in conductivity response caused by water vapors absorption plays a part in the change in probability of intergrain transitions, caused by a change in the dielectric permittivity of polymer matrix. Keywords: Polymers, composites, electrical conductivity. INTRODUCTION The main requirements for the sensing layers of chemical gas sensors, apart from the high sensitivity of their electrophysical properties, are the response selectivity, the signal reversibility and low response time parameters. The materials that suit all outlined requests do not exist yet. The creation of such materials is one of the main problems of modern sensor science and technol- ogy. Nevertheless, some methods by which such materials maybe created are now becoming clearer. One such method is the development of composite materials, which consist of low conducting matrices filled with microcrystals of high conductivity [l, 21 and the investigation of their sensor properties. In some cases, when the matrix only absorbs definite gases or vapors from ambient media, the correct choice of composite composition gives us a possibility to provide the materials required. These exhibit both high selectivity and strong sensitivity needed for detection of definite components from gas mixtures. The experimental data and theoretical re- sults concerning composite materials exhibit the anomalous behaviour of sensitivity of some of its electrophysical characteristics under various external influences in the percolation threshold area (the scal- ing range) of their composition. This phenomenon may also involve the influence of gas species absorption on the electroconductivity of composite materials [ 1,3]. Note, that the mechanisms of such influences might be different. The fact that the main role in the response of conductivity in scaling area, caused by change of external parameters, plays the cooperative factor corresponding to change in geometry and topology of the conducting cluster, rather than the local factor-the change of local electric parameters of structural elements (filler par- ticles) which form that cluster [4]. This principle determines the performance of the application of conducting polymer-composites, applied as thermis- tors [5], pressure sensors [l] and also chemical sensors [l, 21. The main reasons for conductivity response caused by change of such external parameters as temperature, pressure and absorption, are the mech- anical changes in the structure of conducting system, in the terms of percolation theory-the density of infinite cluster (IC) [6]. The heating of the composites, consisting of con- ducting filler (carbon-black, conductive-ceramics) 1613