Microscopic origin of the high-strain mechanical response of poled and non-poled poly(vinylidene fluoride) in the β-phase
Tensile mechanical tests have been applied to poled and non-poled poly (vinylidene fluoride) in its β-phase at several temperatures and strain rates, along the main directions of the material, in order to relate the mechanical response with the microscopic variations of the material, as well as to evaluate the performance of the material under use in different applications and environments. Poling increases mechanical strength along the preferential orientation of the microstructure but does not affect significantly the transversal mechanical properties. By increasing temperature, the effect of poling on the mechanical response is reduced due to increased molecular mobility and consequent de-poling of the system. The activation volume and enthalpy at yielding were calculated within the Eyring formalism. It is concluded that poling increases interaction among dipolar moments within the crystalline lamella and with the surrounding interphase and therefore increases cooperativity. This fact is also demonstrated by the decrease of the KWW β-exponent obtained from the stress-relaxation experiments. 2008 Elsevier B.V. All rights reserved.