Berlin 2012 – scientific programme
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BP: Fachverband Biologische Physik
BP 10: Biopolymers and Biomaterials (with CPP)
BP 10.4: Talk
Tuesday, March 27, 2012, 10:30–10:45, H 1058
Neutron radiography study of water migration into casein micellar films — •Ezzeldin Metwalli1, Helen E. Hermes2, Elbio Calzada3, Stefan U. Egelhaaf2, and Peter Müller-Buschbaum1 — 1TU München, Physik-Department, LS Funktionelle Materialien, James-Franck-Str.1, 85748 Garching, Germany — 2Physik der weichen Materie, Heinrich-Heine-Universität Düsseldorf, 40225 Düsseldorf, Germany — 3Forschungsneutronenquelle Heinz Maier-Leibnitz, TU München, 85747 Garching, Germany
Casein, a milk protein, forms micelles with a radius of about 100-300 nm. Casein-protein based films are widely used as an adhesive for labeling glass bottles and other containers because of their superior mechanical stabilities in different humidities at temperatures between 2 and 40 C. This study demonstrates the use of neutron radiography as a viable method for the determination of the diffusion profile of water in casein films. The dry casein film is contacted with water and neutron radiographs are collected as function of elapsed time. Profiles of the water concentration are successfully measured by imaging. Two diffusion processes are observed: (a) fast diffusion with a decaying diffusion constant, resulting from water exchange with the hydration water bound to the casein proteins, and (b) slow and constant diffusion due to Fickian water transport into the voids and holes between the casein micelles and their aggregates in the porous film. Time evolution of the later diffusion process is compared with our recent GISANS investigation [1] of hydration behavior of casein thin films in water vapor. [1] Metwalli et al., Langmuir 25, 4124 (2009)