Using confocal rheometry to investigate shear thickening suspensions

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1232666PI: CohenThe viscosity of colloidal suspensions can vary by orders of magnitude with shear rate. Such non-Newtonian behavior arises from the arrangement of suspended particles and their mutual interactions. Although numerical simulations and scattering experiments revealed much about the local and average suspension structures, particle dynamics at mesoscopic length scales, where non-Newtonian behaviors are believed to originate, are still poorly understood. This research program will continue to develop techniques that combine fast confocal microscopy with simultaneous rheological measurements to determine how changes in suspension mesoscopic structure alter the suspension viscosity. The current work will focus on three themes associated with shear thickening suspensions. First, we will determine how hydrocluster size distribution alters shear thickening in different size gaps. This task will be achieved by directly visualizing hydroclusters at various shear rates and investigating their behavior under confinement. Second we will determine how particle shape enhances shear thickening. Dimer and cubic particles will be used to investigate how shape anisotropy affects thickening. Finally we will investigate whether mechanisms for thickening at high volume fractions are hydrodynamic in origin or if, as many groups claim, at high volume fractions frictional contact forces come into play. These confocal rheometry techniques illustrate a new approach for determining the microscopic dynamics of non-Newtonian suspensions. Ultimately, research carried out in this project will enable design of shear thickening fluids. Such studies will have substantial ramifications due to the important role that shear thickening materials play in industrial applications. These fluids can be found in materials ranging from paints, to pastes, and even shear thickening drilling mud proposed for ?top kill? procedures (such as those used to control the ?blowout? of the Macondo well). Their handling is substantially complicated by their non-Newtonian behavior during processing and packaging. Thus, the goal of designing flow environments and fluids that when appropriate prevent or precipitate rapid changes in suspension rheology will have substantial impact on common industrial practices.A number of Education and outreach activities will be carried out. The PI is involved in creating performance based presentations on emergent phenomena in science. In addition to this activity, the PI will continue to organize the semiannual New York Complex Matter Workshops. These meetings are aimed at stimulating interaction among soft matter and statistical physics researchers from Syracuse, Cornell, RIT, General Electric, Kodak, Corning and other institutions and industrial labs in the area. The workshops will serve as an excellent opportunity for introducing graduate students and postdocs to the local academic and industrial research community.