Dielectric relaxation behavior of multi-walled carbon nanotube (MWCNT)-reinforced silicone elastomer nanocomposites has been studied as a function of filler loading in a wide frequency range (10 À1 -10 6 Hz). The effect of MWCNT loading on the real and imaginary parts of impedance is distinctly visible. The significant change in the impedance parameters on filler loading is explained on the basis of interfacial polarization in a heterogeneous medium and relaxation dynamics of polymer chains. The electrical modulus formalism has been used to investigate the conductivity and relaxation phenomena of the system. The frequency dependence of ac conductivity is explained using percolation theory. The existence of percolation phenomenon in the composites is discussed on the basis of electrical conductivity and morphology of the composites. The percolation threshold (as studied by electrical conductivity) occurs in the range of 4 phr of MWCNT loading. The scanning electron photomicrographs show agglomeration of the MWCNT above 4 phr concentration and formation of a continuous network structure.
Impedance and dielectric spectra of silicone elastomer nanocomposites were used to study their secondary (α * or β) relaxation behavior as a function of nano-graphite loadings in the frequency range of 10 -1 to 10 6 Hz. The effect of nanographite loadings on real and imaginary parts of complex impedance has been distinctly visible and explained on the basis of interfacial polarization of filler and relaxation dynamics of polymer chains. The effects of nano-graphite loadings on loss tangent, dielectric permittivity, complex dielectric modulus and electrical conductivity have also been studied. The dielectric permittivity of the composites strongly depends up on the extent of nano-graphite concentration and temperature. The conductivity and relaxation phenomenon have been investigated through dielectric modulus formalism. Nyquist plots, ColeCole plots and Argand diagram confirm the existence of non-debye relationship. The frequency dependence of ac conductivity has been investigated by using Percolation theory. The percolation phenomenon has been discussed from electrical conductivity and dielectric permittivity and percolation threshold was found at 6 phr nano-graphite loading. SEM photomicrographs shows well dispersion of nano-graphite.
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 10−1–106 Hz. 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.
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