Molecular Relaxation of the Side Groups in Poly(vinyl alcohol) Films in GHz Frequency Range

摘要

Poly(vinyl alcohol) (PVA) is a synthetic polymer which has been used in a wide variety of applications. This polymer has been extensively investigated by a large number of techniques to shed light about its physical and chemical properties. In this work, for fist time, high frequency (1x10~9-3x10~9 Hz) relaxation process has been observed in the PVA films in the temperature range of -10°C to +120°C. This relaxation exhibits negative activation energy below glass transition temperature Tg and at higher temperature positive activation energy with subsequent saturation. Upon cooling the activation energy was negative again. This high frequency relaxation process and its temperature dependence can be attributed to the interaction of the bounded water and the changes of energy and freedom of movement of OH side molecular chains groups. This conclusion has been supported by in situ FTIR measurements. A possible scenario of this relaxation and dynamics of molecular motion has been proposed.