FICKIAN AND CASE-II DIFFUSION OF WATER INTO AMYLOSE - A STRAY FIELD NMR-STUDY

The ingress of liquid water and water vapour into glassy pellets of th e starch polymer amylose has been studied using stray field nuclear ma gnetic resonance imaging (STRAFI), to produce one-dimensional water co ncentration profiles as a function of depth from the sorption surface, and time. For the vapour experiments the observed concentration profi les are characteristic of a system showing Fickian diffusion with a mu tual diffusion coefficient, a function of the concentration of the pen etrant. In contrast, the ingress of liquid water is non-Fickian; conce ntration profiles characteristic of Case II diffusion have been modell ed semi-quantitatively using the Thomas-Windle model. (C) 1997 Publish ed by Elsevier Science Ltd. All rights reserved.