Swelling-controlled solute diffusion in glassy polymers

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Penetrant transport in glassy polymers has played a major role in traditional engineering applications such as membranes, packaging and barrier materials. More recently, this phenomenon has become increasingly important in applications ranging from micro and nanofabrication to the design of swelling-controlled hydrogels for drug delivery. In the latter case, the presence of a substantial volume swelling and the diffusion of entrapped solute may further complicate the overall rate process. Such swelling and diffusion generally do not follow a Fickian diffusion mechanism. Although the case of a single penetrant transport in glassy polymers has been studied extensively, the effect of initial solute concentration level in the polymer on the solvent penetration characteristics has not been properly studied, and the role of the swelling process in relation to the observed solute release behaviour from glassy polymers, in particular hydrogels, has not been conclusively resolved.