17. Permeation, Diffusion, and Sorption of Gases and Vapors

Publisher Summary This chapter describes the permeation, diffusion, and sorption of gases and vapors. The principal alternative to permeation rate measurements for transport coefficient determinations is the direct measurement of the rate of uptake or loss of a penetrant by a polymer sample. The advantages of the sorption approach are that it eliminates the need for elaborate sealing and the extreme leak sensitivity associated with permeation methods. It reduces uncertainties in the sample surface area caused by membrane supports, and it is well-suited to lengthy experiments on materials in which diffusion coefficients are low. In some instances, the determination of the extent of penetration may be performed by visual inspection, as when the penetrant advances in a well-defined front and swells or crazes the sample. A model that provides a consistently accurate representation of the permeation of gases above their critical temperatures, at atmospheric and subatmospheric pressures, through non-swollen rubbery polymers that do not contain crystallites or fillers is presented. The correlation and estimation of transport and solubility coefficients are also elaborated.