Nonlinear Dielectric Relaxation Spectra of Polyvinyl Acetate

Abstract

The frequency spectra of the linear and third nonlinear permittivities, ε₁ ^* and ε₃ ^*, have been measured for polyvinyl acetate (PVAc) at temperatures above T _g. The Debye relaxation of ε₁ ^* associated with the micro-Brownian motion of noncrystalline segments is found to be accompanied by the complex frequency dependence of ε₃ ^* 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 (\propts ^*ε₁ ^*2) to yield the intrinsic nonlinear dielectric relaxation spectra in the form of Δε₃/(1+iωτ₃)³ in accordance with phenomenological prediction. The evaluated relaxation strengths, Δε₁ and Δε₃, lead to estimates of equivalent Langevin dipoles consisting of eleven monomers and a saturation polarization of 20 mC/m².