ABSTRACT
The molecular mobility is sufficient for maintaining a distribution of free volume and entropy in thermal equilibrium and the corresponding theories are quite acceptable for describing the liquid behaviour. This chapter addresses a question which remains unsolved to date, though far from being definitely clarified in the case of amorphous systems in general and polymers in particular. It considers a glassy solid formed of nitrogen atoms, or molecules or, more generally, structural entities. In the case of amorphous polymers the preliminary motion is due only to the smaller portion of the chain likely to move without movement of the rest of the chain. Condensed matter is considered an assembly of structural units assumed to be spherical; the interaction between these units can be described by the Lennard-Jones potential. The chapter shows the diversity amongst analyses of molecular mobility in amorphous polymers.
