Seminars & Discussions

Complex fluids demonstrate many fascinating non-Newtonian flows. Colloidal suspensions are a particularly interesting complex fluid because they display Newtonian, shear thinning and even shear thickening behaviors at different shear rates. Although the mechanical response of colloids has been studied extensively using conventional rheological techniques, without direct imaging of the suspension microstructure it has been difficult to elucidate the mechanisms underlying the suspension's non-Newtonian response. Here, we use a fast confocal-rheoscope to study the structure response of sheared colloidal suspensions and relate this response to their rheological properties. In this talk, I will introduce this general experimental approach of linking microstructure with rheological properties. I will also illustrate the capabilities of this approach by presenting results about the shear thinning , shear induced structure, and shear thickening behavior of this fascinating class of materials.

Molecular spiders are synthetic bio-molecular systems with "legs" made of short single-stranded segments of DNA. Spiders move on a surface covered by single-stranded DNA segments complementary to the legs, and the legs can attach to them. When a leg detaches from a segment on the surface, it can attach to a neighboring segment, and the spider moves. We are interested in the speed and diffusion coefficient of spiders on one and two dimensional surfaces. Mappings to exclusion processes and many open problems will be discussed.

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