Intrinsic mobility of molecular glasses

The dielectric relaxation study of glass-forming liquids show the presence of two relaxation regions at temperatures above TQ. The low frequency relaxation is attributed to the cooperative rearrangement of molecules. The high frequency relaxation, which continues to exist in the glassy state, is suggested to arise from the hindered rearrangement of the molecules encaged by large regions which have been made relatively immobile by the stringent requirement of a cooperative motion. The hindered reorientation of dipoles in liquids at low viscosity has about the same Arrhenius energy as the β process seen in glasses. The results emphasize the role of intermolecular potential barriers in producing relaxation characteristics which have been generally accepted to arise from intramolecular rearrangement.