Berlin 2012 – wissenschaftliches Programm

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BP: Fachverband Biologische Physik

BP 10: Biopolymers and Biomaterials (with CPP)

BP 10.4: Vortrag

Dienstag, 27. März 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)