Application of periodically modulated driving force to the transition kinetics in vinylidene fluoride/trifluoroethylene copolymers

Abstract

The method of “modulated driving force” has been applied to the kinetics of ferroelectric–paraelectric transition in copolymers of vinylidene fluoride (VDF) with trifluoroethylene (TrFE). The method examines the response of transition kinetics to a periodically modulated driving force, e.g., supercooling or superheating. The response to the modulation in temperature appears in the apparent heat capacity obtained by a temperature-modulated differential scanning calorimeter. By examining the frequency dispersion and its dependence on underlying linear heating (or cooling) rate, the mean time required for the completion of transition in each crystallite and the dependence of transition rate on superheating (or supercooling) are obtainable. In VDF/TrFE copolymers, it is known that the transition behavior undergoes a drastic change from reversible transition with low VDF content to nucleation-controlled transition with higher content. Several types of compositions (VDF/TrFE=47/53, 52/48, 59/41, 65/35, 69/31 and 73/27 by mol %) have been examined experimentally with this method in terms of the crossover of transition behaviors.