A delay of percolation time in carbon-black-filled conductive polymer composites

This work attempts to determine how percolation at an equilibrium state is correlated to percolation under experimental conditions. The dynamic proces s of forming conductive networks in carbon-black (CB)-filled poly(methyl me thacrylate) composites was investigated by real-time tracing the time depen dence of electrical resistivity during isothermal treatments. It was observ ed that the dynamic percolation curves maintains the same shape and shift t o a shorter percolation time with increasing annealing temperature and fill er concentration. An Arrhenius plot of the shift factor against the anneali ng temperature shows a linear relationship, irrespective of the filler conc entration, and the activation energy of the percolation time is close to th e activation energy of the zero-shear-rate viscosity of the polymer matrix. Furthermore, an increase in the thermodynamic interactions between CB and the polymer matrix causes a large reduction in polymer mobility, resulting in an increase in the percolation time. These results lead to the conclusio n that percolation is delayed by the bulk mobility of polymer layers surrou nding CB particles. An experimental approach for determination of the retar dation time is proposed based on theoretical analysis of the dynamic moveme nt of the carbon particles. It is suggested that the difference in the kine tic history with respect to percolation among different composite systems c an be eliminated by normalizing the experimental conditions to the same val ue of retardation time. (C) 2000 American Institute of Physics. [S0021-8979 (00)05515-8].