EFFECT OF INTERFACIAL ENERGY AND VISCOSITY ON PERCOLATION TIME OF CARBON BLACK-FILLED POLY(METHYL METHACRYLATE)

The dispersion state of carbon black (CB) particles in a polymeric matrix was found to be affected by such factors as interfacial energy of the CB-polymer interface and the melt viscosity of matrix polymers. At a given CB volume fraction, the electrical conductivity of CB-filled poly(methyl methacrylate) (PMMA) was measured as a function of time at a temperature higher than the glass transition temperature (T-g). At a characteristic time, as a result of the aggregation of CB, networks facilitating electrical conduction were formed and a percolation-like transition was observed. We defined this characteristic time as the percolation time (t(p)) and estimated the dispersion state of particles by the t(p). The effects of interfacial energy of the CB-polymer interface and melt viscosity of the matrix were estimated quantitatively by changing the surface energy of CB and the temperature. The experimental values of t(p) were compared to the calculated values using a simple model. The percolation time decreased with increase of interfacial energy and CB content, and increased with the matrix viscosity. The model well explains the dependency as long as the volume fraction of CB is not large and matrix viscosity is neither very small nor very large.