NONLINEAR DIELECTRIC RELAXATIONS OF POLYMERS

Non-linear dielectric relaxation spectra have been measured for various vinylidine cyanide co-polymers and polyvinyl acetate. It is shown that the third-order permittivity depends upon frequency according to epsilon-3* = DELTA-epsilon-3/(1 + i-omega-tau-3)3 with negative DELTA-epsilon-3, when the linear permittivity, epsilon-1*, exhibits a Debye relaxation. Combinations of DELTA-epsilon-1 and DELTA-epsilon-3 allow estimates of the effective moment and correlation length of dipoles. The large permittivities of vinylidene cyanide co-polymers ranging from 20 to 130 are attributed to strong dipolar correlations. Polyvinyl acetate shows deformed spectra due to the electrostriction which makes a positive contribution to DELTA-epsilon-3 in the low-frequency regions.