NONLINEAR DIELECTRIC-RELAXATION SPECTRA OF POLYVINYL ACETATE

The frequency spectra of the linear and third nonlinear permittivities, e1* and e3*, have been measured for polyvinyl acetate (PVAc) at temperatures above T(g). The Debye relaxation of e1* associated with the micro-Brownian motion of noncrystalline segments is found to be accompanied by the complex frequency dependence of e3* due to combined contributions from the intrinsic nonlinear dielectricity and the electrostriction. Additional measurements for the elastic compliance s* allow subtraction of the latter contribution (infinity s*e1*2) to yield the intrinsic nonlinear dielectric relaxation spectra in the form of DELTA-e3/(1 + i-omega-tau-3)3 in accordance with phenomenological prediction. The evaluated relaxation strengths, DELTA-e1 and DELTA-e3, lead to estimates of equivalent Langevin dipoles consisting of eleven monomers and a saturation polarization of 20 mC/m2.