THE STABILITY AND AGING OF POLED POLYVINYLIDENE FLUORIDE (PVF(2)) ELECTRETS

The stability and aging of piezoelectricity in corona charged Form 2 PVF(2) have been investigated with respect to annealing temperature and ultraviolet exposure. Little decay is observed with annealing temperatures of up to 100 degrees C. The original activity decays by about half after annealing at 150 degrees C showing superior aging characteristics of Form 2 films compared to stretched and poled films of the Form 1. The stability of the structure of poled Form 2 crystallites is demonstrated by X-ray diffraction data which suggest that at least part of the decay of piezoelectricity after high temperature treatment is due to melting and subsequent recrystallization of the polymer. Exposure to ultra-violet radiations does not produce additional loss of piezoelectric activity. This suggests that space charges contribute less than 10% to the d(31) piezoelectric coefficient of poled Form 2 PVF(2).