Structure-electrical conductivity of polyvinylidene fluoride/graphite composites

Graphite powder was introduced into polyvinylidene fluoride via the solution mixing technique. The composites were then subjected to hot compression molding. The effect of dispersion of graphite particles and electrical conductivity of the composites were investigated. Solution mixing enabled homogeneous dispersion of graphite powder within the polyvinylidene fluoride matrix as revealed by transmission electron microscopy. X-ray diffraction and Fourier transform infrared spectroscopy analysis revealed that graphite incorporation induced the alpha-phase of polyvinylidene fluoride. The DC conductivity results showed that the conductivity increased with an increase in graphite content. Beyond a critical concentration of graphite, percolation threshold, (Phi(c) = 2.3 vol%) the conductivity increases by five orders of magnitude at 3.9 vol% of graphite powder composite. The electrical conductivity was approximately constant for the composites with the higher graphite loading. Consequently, adding more graphite powder did not significantly alter the electrical conductivity. The correlation between the dispersion of graphite particles and electrical conductivity was discussed. The AC conductivity of composites was investigated in a wide range of frequencies from 50 Hz to 5 MHz and at temperatures ranging from room temperature to 180 degrees C. The conductivity of the composites exhibited strong frequency dependence particularly in the vicinity of the electrical percolation threshold. sigma(AC) obeyed the power law of the form: sigma(AC) = A(T)center dot omega(S(T)), where omega is the angular frequency and s and A the characteristic parameters. The values of the exponent (s) were found to decrease with increasing temperature which is consistent with the correlated barrier-hopping model.