CONTINUUM SPACE SIMULATION AND EXPERIMENTAL CHARACTERIZATION OF ELECTRICAL PERCOLATION BEHAVIOR OF PARTICULATE COMPOSITES

A model for predicting the percolation threshold of electrical conductivity of particulate composite materials is presented. The model consists of an impermeable hard core and a permeable soft shell. The hard core represents the physical inclusion while the permeable shell represents the effective range for electron transfer in the matrix polymer. The simulation procedure utilizes the method of gradual addition of inclusions into a finite volume to probe the existence of a three-dimensional percolating network. After each a addition of the inclusion, the microstructure is examined by updating the connectivity matrix to check if a percolating network has been formed. From the onset volume fractions for percolation of various finite systems, the threshold in an infinite system was calculated by extrapolating the data according to the finite size scaling theory. A value of 0.89 was observed for the correlation length exponent, which matches well with values of almost-equal-to 0.9 reported in literature. The critical volume fractions for percolation for different ratios of shell thickness to diameter are compared with the experimental conductivities of polyethylene composites filled with various grades of nickel powder. It is shown that the shell thickness can be estimated from the experimental threshold of one grade of nickel filled composite, and this shell thickness can be used to predict the percolation thresholds of composites filled with other grades of nickel powder. The effects of particle size distribution and non-random spatial distributions are also discussed.