Microstructural changes through the ferroelectric transition of P(VF₂ – TrFE) copolymers investigated using synchrotron radiation

Abstract

Random copolymers of vinylidene fluoride (W2) with trifluoroethylene(TrFE) spontaneously crystallize into a ferroelectric structure (for a VF₂ content ranging from 60% to 80%)^1,2 On account to their high degree of crystallinity, they exhibit strong, piezoelectric and Wroelectric activities (after poling)^3,4. Upon heating, these copolymers undergo a clear ferroelectic transition of first order type: the planar trans-trans conformation of the chain (with a large dipole moment per unit cell) transforms into random sequences of TG, and TT conformations. Using the Synchrotron Radiation Facility at LURE we investigated the evolution of small-angle and wide-angle X-ray scattering patterns during successive annealing cycles of 70/30 P(W2-TrFE) copolymers, initially quenched from the melt^5,6. Thus the reversible effects of the Curie transition can be discussed separately from the irreversible effects of annealing. The small divergence of the S.R. permits high resolution measurements and its high brilliance allows real time investigations to be made especially during the ferroelectric transition.