SOLUTE AND PENETRANT DIFFUSION IN SWELLABLE POLYMERS .7. A FREE VOLUME-BASED MODEL WITH MECHANICAL RELAXATION

Penetrant transport through and solute release from continuously swelling polymers is viewed as a process associated with major structural changes in the polymer morphology. Changes in the diffusivities of penetrant and solute reflect a free volume mechanism for transport. The polymer is initially glassy with a uniform dispersion of solute. After the system is placed in contact with a thermodynamically good penetrant, a glassy/rubbery phase transition occurs at a well defined swelling interface. The penetrant fractional uptake, solute fractional release, sample dimensions, swelling front position, and instantaneous swelling interface number are determined and related to the nature of the swelling process.