Dresden 2003 – scientific programme

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DY: Dynamik und Statistische Physik

DY 46: Poster

DY 46.7: Poster

Thursday, March 27, 2003, 15:30–18:00, P1

Depletion forces in purely entropic systems — •Laurent Helden, Valetin Blickle, Paul Leiderer, and Clemens Bechinger — University of Konstanz, Fachbereich Physik, D-78457 Konstanz, Germany

The stability and phase behavior of colloidal suspensions containing particles of different size and shape is known to be strongly influenced by depletion forces. Various kinds of colloids as for example spheres, rod- and disc-like Particles or polymeres can serve as depletion agent. The depletion forces they induce can lead even in systems where all pair interactions are purely repulsive to attractive forces which may finally cause particle flocculation. Accordingly, the understanding of these forces is besides fundamental interest also essential for industrial processes. The technique of total internal reflection microscopy (TIRM) is capable to measure these weak depletion interactions with a force resolution in the order of 10 fN. Here we present the first direct measurement of depletion potentials between a sphere and a flat surface caused by rod-shaped boehmite-particles additionally dispersed in the solvent. All other interactions, in particular electrostatic and dispersion forces were effectively screened either by the addition of salt or by silica coatings. Accordingly, the system can be regarded as a good model for purely entropic interactions.