DETECTION OF FERROELECTRIC TO PARAELECTRIC PHASE-TRANSITION IN COPOLYMERS OF VINYLIDENE FLUORIDE BY MAGNETIC-SUSCEPTIBILITY

The diamagnetic susceptibility of a series of random copolymers of vinylidene fluoride (VF2) With trifluoroethylene containing 60 to 100 mole-% VF2 has been investigated, both as a function of composition and of temperature. Results show that at room temperature the molecular susceptibility of the series linearly decreases with VF2 content. Furthermore, the diamagnetic susceptibility for each composition rises gradually at the beginning of the Curie transition, reaching a plateau which characterizes the diamagnetism of the paraelectric phase. The percent increase in diamagnetism when passing from the ferroelectric to the paraelectric phase is primarily due to the changes occurring from the planar all-trans polar conformation into the disordered molecular conformation of the high temperature phase. The reduced final increase in diamagnetism detected at the melting point suggests that conformational transformations occurring from the paraelectric phase into the molten state are small.