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8425520 
Journal Article 
Diffusion and relaxation in glassy polymer powders: 2. Separation of diffusion and relaxation parameters 
Berens, AR; Hopfenberg, HB 
1978 
1 
Polymer
ISSN: 0032-3861 
ELSEVIER SCI LTD 
OXFORD 
19 
5 
489-496 
English 
WOS:A1978EX94900002 
Gravimetric sorption measurements for organic vapours in monodisperse glassy polymer powders have shown widely varied non-Fickian kinetic behaviour. These varied kinetics are interpreted by a single mathematical model involving a linear superposition of one or two phenomenologically independent first order relaxation terms upon the ideal Fickian diffusion equation. Analysis of experimental data for submicron powders through this model yields kinetic and equilibrium parameters describing the individual contributions of the diffusion and relaxation processes. This analysis has been applied to both integral and incremental sorption data for vinyl chloride, acetone, and methanol in poly(vinyl chloride) and for n-hexane in polystyrene. Sorption by initially penetrant-free polymer samples is dominated by a rapid Fickian diffusion process, while incremental sorptions show larger relative contributions from slow relaxation processes. The relaxation processes appear to be related to slow redistribution of available free volume through relatively large scale segmental motions in the relaxing polymer. The diffusion-relaxation model seems to provide a meaningful analysis of several non-Fickian 'anomalies', including a very slow approach to apparent equilibrium, two-stage and sigmoidal sorption curves, and sorption curves involving an initial maximum followed by temporary desorption and subsequent resorption. © 1978.