The Model for Description of Electrical Properties of Polymerization-Filled Composite Materials
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Moscow,
RUSSIA
ABSTRACT The conductivity behavior found in polymerization-filled composites differs from that predicted by percolation theory and can be explained by a simple model predicting the existence of two characteristic values in such systems: the radius of filler particles and the distance of charge penetration into polymer matrix. Detailed mechanisms, responsible for such peculiarities in charge transfer are also discussed. INTRODUCTION The paper describes our study of the behavior of some polymerization-filled in characteristics electrophysical composites (PFC) with conducting filler. There are two main types of conductive composites: matrix spatial position of filler in which an order in mixtures, particles particles exists and stochastic mixtures, where filler are distributed in full disorder. Which of these two types is the realized depends on the method of composite fabrication, particles and the interaction between filler properties of filler and polymer matrix. Stochastic composites filled with conducting particles show characteristic percolation behavior with phase transition which takes place when conduction mechanism changes from conduction through polymer matrix, usually negligible, to conduction through particles. This change an infinite cluster of conducting filler of mechanism is usually accompanied by a drastic increase of c, constant conductivity a, surge of dielectric composite reversal of magnetoresistance sign and change in behavior of other electrophysical characteristics. Position of dielectric-metal transition (or threshold) Vf and behavior of conductivity of composites is predicted by the so-called continuum problem of percolation theory. In the case of particles predicted value random distribution of spherical filler 16 vol.% and concentration dependence of for V; is about conductivity beyond the threshold is given by the expression:
a=
0 o(V.f-VP),
(1)
and where a0 is a constant, Vf is volume concentration of filler t is conductivity critical index, approximately equal to 1.9. There exist many systems, e.g. cermets [1] and polymer composites [2] for which percolation behavior is in good agreement with percolation theory. But we have observed in a number of cases for polymerization-filled composites with spherical particles, having narrow size dispersion, essential deviations for both Vf and t values from those predicted by percolation theory: V, theor=16 45 Mat. Res. Soc. Symp. Proc. Vol. 318. @1994 Materials Research Society
and ttheor=1. 9 [3,4]. An attempt to describe this experimental situation on the basis of a simple model for such polymer composites is undertaken in the present paper. The analysis of mechanisms which lead to such anomalies in percolation behavior of conducting polymer composites has also been performed and the results are described below. EXPERIMENTAL The objects of investigation were polymerization-filled one consisting of aluminum polymer composite systems: the first particles, dispersed in a matrix of polypropylene (PP) and the second system was
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