ABSTRACT
This chapter focuses on the behavior and prediction of the diffusion coefficients for volatile residuals-polymer systems. The fundamental principles associated with the Vrentas-Duda models for self- and binary mutual diffusion shall be developed for solutions containing uncross-linked amorphous polymer chains and low- molecular-weight solvents. Solvent self-diffusion is the process by which a molecule undergoes a random walk in a homogeneous medium. A nonsolvent such as water is added to devolatilization processes to enhance the mass transfer. In many of the cases, the enhancement realized is not due to an increase in the effective diffusion coefficient; it is related to a reduction in the effective diffusion path associated with the formation of new surface area by bubbling or foaming of the added volatile material. Devolatilization usually occurs at elevated temperatures where anomolous effects associated with many polymeric diffusion processes are not observed.
