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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 16: SYMPOSIUM Driven Soft Matter I

CPP 16.1: Invited Talk

Tuesday, February 26, 2008, 09:30–10:00, C 130

Imaging the flow of concentrated colloidal suspensions — •Wilson Poon, Lucio Isa, and Rut Besseling — The University of Edinburgh, Scotland, UK

Recent advances in confocal microscopy allow us to image the flow of concentrated colloidal suspensions at single-particle resolution in real time. I will describe results from recent experiments on suspensions of hard spheres at packing fractions of 60% or higher. At zero applied stress, these suspensions behave like amorphous solids (‘colloidal glasses’). We have used fast confocal imaging to study the yielding of such suspensions under simple shear, as well as their flow in rectangular capillaries. In both cases, direct imaging has revealed a rich variety of phenomena not predicted by traditional rheological theory treating dense suspensions as yield stress fluids. In the case of pipe flow, we find that a theory previously proposed for granular materials can give a good account of certain aspects of our observations.