title: Kinks in experimental diffusion profiles of a dissolving semi-crystalline polymer explained by a concentration-dependent diffusion coefficient.
abstract: The dissolution of polyethylene oxide (PEO) tablets in water has been followed in situ by neutron radiography. When in contact with water, the crystalline phase of semi-crystalline PEO melts once a certain water content is attained. Polymer concentration profiles obtained from the neutron transmission images exhibited a pronounced kink which corresponds to a sharp front in the images and which is related to the melting transition. Sharp diffusion fronts and phase transitions are often linked to non-Fickian behaviour. However, by considering the time evolution of the complete concentration profiles in detail it is shown that the dissolution process can be explained using Fickian diffusion equations with a concentration-dependent diffusion coefficient.
authors.affiliation: Condensed Matter Physics Laboratory, Heinrich Heine University, D-40225 Düsseldorf, Germany. helen.hermes@uni-duesseldorf.de.
authors.forename: Helen E
authors.initials: HE
authors.lastname: Hermes
authors.forename: Christoph E
authors.initials: CE
authors.lastname: Sitta
authors.forename: Burkhard
authors.initials: B
authors.lastname: Schillinger
authors.forename: Hartmut
authors.initials: H
authors.lastname: Löwen
authors.forename: Stefan U
authors.initials: SU
authors.lastname: Egelhaaf