Super Case II Transport of Organic Vapors in Glassy Polymers
Alfrey, Turner, and Lloyd have defined Fickian transport and Case II transport as the two limiting cases for the transort of an organic penetrant through an amorphous glassy polymer.1 Fickian transport refers to the interdiffusion of penetrant and polymer described by Fick’s equations. In general, Fickian diffusion is only observed in glassy systems when the penetrants are simple gases, solvents with small molecular diameters, or partial solvents at very low temperatures and penetrant activities. At temperatures and penetrant activities where partial solvents swell the polymer, transport is often controlled by a combination of polymer relaxation and Fickian diffusion mechanisms. Case II transport occurs when the sorption is entirely controlled by stress-induced relaxations taking place at a sharp boundary separating an outer swollen shell, essentially at equilibrium penetrant concentration, from an unpenetrated glassy core. Ideally, this sharp boundary moves through the polymer at a constant velocity during Case II transport.
KeywordsFront Velocity Polystyrene Film Constant Rate Period Phenylene Oxide Normal Hexane
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