Imaging the microscopic structure of shear thinning and thickening colloidal suspension
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The viscosity of colloidal suspensions varies with shear rate, an important effect encountered in many natural and industrial processes. Although this non-Newtonian behavior is believed to arise from the arrangement of suspended particles and their mutual interactions, microscopic particle dynamics are difficult to measure. By combining fast confocal microscopy with simultaneous force measurements, we systematically investigate a suspension's structure as it transitions through regimes of different flow signatures. Our measurements of the microscopic single-particle dynamics show that shear thinning results from the decreased relative contribution of entropic forces and that shear thickening arises from particle clustering induced by hydrodynamic lubrication forces. This combination of techniques illustrates an approach that complements current methods for determining the microscopic origins of non-Newtonian flow behavior in complex fluids.
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We thank T. Beatus, Y.-C. Lin, J. Brady, L. Ristroph, and N. Wagner for useful discussions. This research was supported by grants from NSF Civil, Mechanical, and Manufacturing Innovation, Division of Materials Research (DMR), and DMR Materials Research Science and Engineering Centers, and in part by award KUS-C1-018-02 from King Abdullah University of Science and Technology (KAUST). J.N.I. was supported by the U.S. Department of Energy, Division of Materials Sciences and Engineering under award DE-FG02-87ER-45331.
AMERICAN ASSOCIATION ADVANCEMENT SCIENCE
CONCENTRATED SUSPENSIONS; DENSE SUSPENSIONS; RHEOLOGY; FLOW; DISPERSIONS; SIMULATION; SPHERES
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Science 2 September 2011: Vol. 333 no. 6047 pp. 1276-1279 DOI: 10.1126/science.1207032