Atomistic Modelling of Processes Involved in Poling of Pvdf

Marta M. D. Ramos, Helena M. G. Correia, S. Lanceros-Méndez Departamento de Física, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal Abstract Poling processes play an important role in the design and preparation of many ferroelectric materials for practical uses in the field of sensors and actuators. Particularly, the processing of piezoelectric β-poly(vinylidene fluoride) (β-PVDF) involves mechanical stretching in order to transform the extruded α-phase into the β-phase and poling of this later material in order to optimise the piezoelectric response. This poling process affects the orientation of the dipolar moments of the β-chains and improves the α to β transformation. Poling processes in general and in PVDF in particular are still quite empirical because a firm understanding of the physical processes involved in poling has not been fully established. In the present work we use a self-consistent quantum molecular dynamics method to study the effect of the electric field on both α and β chains of PVDF. The orientation of the dipolar moments in each chain as a function of an electric field and the accompanying structural modifications due to these reorientations will be the main parameters discussed. The theoretical results will be used to better understand the changes at a molecular level due to the poling process, as observed in FTIR experiments, performed in poled and non-poled βPVDF from the same batch.