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Solute and penetrant diffusion in swellable polymers. VII. A free volume‐based model with mechanical relaxation
Author(s) -
Lustig Steven R.,
Peppas Nikolaos A.
Publication year - 1987
Publication title -
journal of applied polymer science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.575
H-Index - 166
eISSN - 1097-4628
pISSN - 0021-8995
DOI - 10.1002/app.1987.070330221
Subject(s) - penetrant (biochemical) , swelling , polymer , materials science , fick's laws of diffusion , diffusion , thermodynamics , polymer chemistry , chemistry , composite material , organic chemistry , physics
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 Fickian equations with concentration‐dependent diffusivities and moving boundaries are solved simultaneously in polymer‐fixed coordinates. A constitutive relation is used to describe the effect of macromolecular relaxations on the rate of volume expansion as the polymer swells. 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.