Molecular diffusion in polymeric systems

Molecular diffusion of polymer chains and low molecular weight constituents and impurities can be an important process in the formation and application of polymer composites. Molecular diffusion in polymer systems is a complex process which can be a strong function of temperature, concentration, polymer molecular weight and polymer morphology. During the last decade, significant advances have been made in understanding the fundamentals of molecular migration in polymeric systems and in predicting and correlating diffusion coefficients of such systems. The main objective of this paper will be to review these recent advances which can serve as precursors for the development of basic theories to describe diffusion through polymer composites. Emphasis will be placed on the description of molecular diffusion in a binary system consisting of a polymer and a low molecular weight solvent or penetrant at the limit of high polymer concentration. The influence of temperature, concentration as well as polymer and penetrant characteristics on the molecular migration process will be considered. Also, the influence of the glass transition temperature and the complications associated with the coupling of molecular diffusion and polymer chain relaxation will be discussed.