INFLUENCE OF THE CRYSTALLINE PHASE ON THE MOLECULAR MOBILITY OF PVDF

Dielectric relaxation and pyrocurrent of PVDF were studied by thermost imulated current spectroscopy. The transition spectrum of the material was investigated by differential scanning calorimetry. Two well-resol ved relaxation peaks have been observed in the temperature range [-100 -100 degrees C]. The molecular mechanisms of these phenomena have been discussed, based on a comparative study of alpha-PVDF and beta-PVDF. The beta relaxation mode is located at -41 degrees C in alpha-PVDF and is slightly shifted toward higher temperatures in the stretched mater ial. This mode has been ascribed to the dielectric manifestation of th e glass transition (T-g) of PVDF. It is comprised of two components co rresponding to the free and constrained amorphous phases, respectively , in the order of increasing temperatures. The alpha(c) transition/rel axation has been associated with molecular motions in the crystalline/ amorphous interphase. At higher temperatures, a compensation phenomeno n corresponding to cooperative movements liberated at the Curie transi tion has been observed in beta-PVDF. (C) 1993 John Wiley & Sons, Inc.