Berlin 2008 – wissenschaftliches Programm

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 7: POSTERS Rheology

CPP 7.5: Poster

Montag, 25. Februar 2008, 16:45–19:00, Poster A

Interfacial Shear Rheology of Coffee Samples — •Jörg Läuger and Patrick Heyer — Anton Paar Germany, Ostfildern, Germany

Coffee is a complex dispersion, which for many coffee drinks is topped by a foam structure of tiny bubbles, e.g. the espresso foam. Interfacial rheology does not probe the foam itself, but measures the adsorption of the amphiphilic ingredients and their network formation at the liquid surface. Higher values of the interfacial properties and a faster film formation are expected to correlate with a better foam stability. Measurements on the film formation process and on the interfacial rheological properties of the final film of coffee samples are presented and discussed. Both oscillatory and rotational test have been performed on films with different coffee concentrations. Different techniques have been used to measure interfacial shear properties. Here we would like to focus on two geometries, which have been used in combination with standard types of rotational rheometers. One is the biconical geometry and the other the De Noüy ring. The aim of the paper is twofold: First, to show that interfacial rheology is a valuable tool to get information on the film formation and therefore the foam stability of coffee, and second, to compare the results obtained by a biconical disc geometry and a Du Nuöy ring.