(519a) Direct Visualization of Near-Wall Structure of Sheared Monosized Suspensions

High-speed confocal microscopy is used to visualize the structure of flowing suspensions in a microchannel at various shear rates.  From these images, real-space particle locations are determined and structure factors are resolved with resolution that allows calculation of the hydrodynamic stresses.  Near the wall of the microchannel, the structure of this suspension depends on the topology of the boundary.  Smooth walls result in particle chaining in the flow direction and higher order organization of these chains.  This order penetrates many particle diameters into the channel.  In contrast, rough walls reduce the effect of the boundary on the suspension microstructure.  Greater than ~6 particle diameters from the boundary, the suspension behaves roughly as seen in the bulk.  Away from the boundary, we visualize hydroclusters that result in the shear thickening at higher Péclet number flows.  We analyze the internal structure and orientation of these hydroclusters and investigate their distributions over multiple scans.