Relaxation behavior of nanographite-reinforced silicon elastomer nanocomposites

Abstract

Dynamic mechanical and dielectric relaxation spectra (DRS) of nanographite-reinforced silicon elastomer nanocomposites were studied. Scanning electron microscopic photomicrographs show well dispersion of nanographite in elastomer matrix. The primary relaxations (α transition and glass transition) have been studied by dynamic mechanical analysis as a function of temperature (−100 to 100°C) at a frequency of 1 Hz and at 1% strain. Irrespective of the nanographite loading, all nanocomposites show glass transition temperature in the range of −11 to −6°C, which was explained on the basis of the relaxation dynamics of silicon matrix. Storage modulus ( E′) shows elastic property and loss modulus shows viscous property of silicon nanocomposites as a function of temperature. Cole–Cole plots exhibit nonlinearity in the nanocomposite matrix. The nonlinearity in the plot between tan δ and E′ is explained by the concept of nanographite silicon interactions and the aggregation of the nanographite. The secondary relaxation (secondary, α* or β) has been studied using DRS in the frequency range of 10−1–106Hz. The capacitance of the nanocomposite is expressed in terms of dielectric permittivity and explained on the basis of polarization of the nanographite in the silicon matrix. The dielectric modulus formalism has been utilized to further investigate the conductivity and relaxation phenomenon. Argand diagram confirms the existence of non-Debye/nonlinear relationship. The percolation threshold as studied by conductivity and dielectric permittivity measurements is found to be at 6 phr nanographite loading.