Simultaneous dielectric and dynamic mechanical measurements on PVDF in the molten state: Study of the linear/nonlinear viscoelastic transition

Abstract

Simultaneous dielectric and dynamic mechanical measurements on PVDF in the molten state have been performed by a dynamic rheometer equipped with an electrical cell. This device permits the evolution of the dielectric and mechanical properties to be recorded both inside and outside the linear viscoelastic domain (LVD). Dielectric properties during shear experiments inside the LVD are not dependent on the shear rate, according to linear viscoelastic theory and Brownian motion considerations. The linear/nonlinear transition is depicted by a fall of conductivity as well as the presence of a maximum of the real part of the permittivity. The decrease of specific conductivity results from modification of the conductive paths, which demonstrates ionic mobility that is different in the direction along and normal to the chain, whereas the maximum of real permittivity is correlated to anisotropic dielectric properties. Stopping the dynamic mechanical strain causes a return of the dielectric parameters to a level close to the one obtained inside the linear viscoelastic domain.