Poling influence on the mechanical properties and molecular mobility of highly piezoelectric P(VDF-TrFE) copolymer

Abstract

The calorimetric, dielectric, and mechanical responses of highly piezoelectric 70/30 P(VDF-TrFE) displaying homogenous d33 of 219 pC N21 are studied. This work aims at better understanding the influence of poling on the mechanical properties of this copolymer. To explain the one decade mechanical modulus drop observed across the Curie transition, a stiffening process of the amorphous phase due to the local electric fields in the ferroelectric crystals is proposed. In poled P(VDF-TrFE), these fields are preferentially aligned resulting in a more stable and higher modulus below the Curie transition. This hypothesis accounts for the lower dielectric signals obtained with the poled sample. Through the Curie transition, the vanishing of these local electric fields, stemming from progressive disorientation and conversion of ferroelectric crystals to paraelectric ones, releases the constraints on the amorphous phase, leading to a storage modulus drop typical of a viscoelastic transition.