Characteristics of dielectric relaxation and low-frequency conduction in silicone rubber composite

The microstructure and charge transport mechanisms of silicon rubber (SR) composite are the key influential factors for its dielectric performance. This study reports on the dielectric response of the silicon rubber composite by dielectric spectroscopy and discusses the molecular chain relaxation and electric conduction characteristics of the composite. The experimental results show that an obvious chain relaxation response exists under low temperature (< 0 ^oC). The composite permittivity behavior as a function of frequency was found to follow the Debye relaxation theory. Over the temperature range from 0 to 100 ^oC, a significant increase of permittivity under low frequency was observed, indicating a kind of interfacial polarization and a distinct electric conduction at low frequency. The dielectric relaxation at high temperature and middle frequency becomes wider and is hidden by the conduction. The conduction process under low frequency and the parameters of the dielectric responses were obtained using the Cole-Cole polarization model. After analysis, a longer relaxation time and a lower activation energy than usual were calculated, possibly due to the restricted molecular chain movements under the low-temperature condition and middle-frequency range. Additionally, a strong thermally assisted conduction process seemingly occurs inside the sample. This would possibly stem from the ionic conduction associated with impurities and charge carrier transport at the interfaces (hopping conduction). The estimated activation energy of the conduction was found to be 0.23 eV according to the Arrhenius equation.