The swelling of a polymer glass by sorption of a small molecule penetrant is considered in a regime characterized by sohyphen;called casehyphen;II diffusion. Attention is focused on the polymer so that the swelling process can be investigated apart from diffusion. The model of Thomas and Windle (TW) is used to predict the surface swelling as a function of exposure time. This model assumes that the swelling is driven by the osmotic pressure which relaxes to zero as the surface penetrant volume fraction fgr;sapproaches its equilibrium value fgr;e. The ratehyphen;controlling factor of the swelling process is the viscosity of the polymer eegr;, which decreases with increasing surface sorption according to eegr;=eegr;0thinsp;exp(minus;mfgr;) where eegr;0is the viscosity of the unswollen polymer. For large values ofM=mfgr;e, fgr;sis very small until a time tgr; is reached beyond which the swelling then accelerates rapidly towards its equilibrium value. This feature is absent ifMe. The time tgr; is estimated by asymptotic analysis. Rutherford backscattering spectrometry is used to investigate the surface swelling kinetics of polystyrene by iodohexane. The TW model tends to underestimate the swelling rate when fgr;sis low and to overestimate it when fgr;sis high. Nevertheless, the time for fgr;sto approach its equilibrium value fgr;eis approximated well by the TW model.
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