Direct Observation of Crystal Transformation Process of Poly (vinylidene fluoride) under High Pressure by PSPC X-Ray System

Abstract

A PSPC (position sensitive proportional counter) X-ray system was employed to directly observe the crystal transformation processes of poly (vinylidene fluoride) at high pressures and high temperatures. X-ray diffraction measurements performed with a heating rate of 5°C/min have revealed that Form I structure is formed after the melting of Form II structure at high pressures above 3,500 kg/cm2. This result provides a solid proof for the origins of multiple endothermic peaks observed in the DTA melting trace at high pressures. Changes in X-ray diffraction patterns during annealing process at a temperature below the melting temperature of Form II structure under 4,000 kg/cm2 were followed and it has been shown that Form II structure performs a crystal transformation into Form I structure with an activation energy of about 30 kcal/mol.