MOLECULAR MOBILITY IN THE LIQUID GLASS-TRANSITION RANGE - COOPERATIVE MOTIONS

A microscopic approach of relaxation effects in the liquid-glass transition range is presented. Due to the disorder, the molecular mobility is easier in sites corresponding to local enthalpy and entropy excess (quasi-punctual defects: QPD). Outside these QPD, the motion of a structural unit implies a set of correlated motions connected in series. This model explains the high values of apparent activation energy and predicts the macroscopic behaviour usually described by the Kohlrausch function. However, in the low-temperature range, in addition to these correlation effects, a parallel distribution of elementary times is needed to explain the experimental features.