When a concentrated suspension of particles such as rigid spheres flows through a narrow channel, there is a tendency for the particles to migrate away from the walls and toward the center of the channel. This phenomenon is called shear-induced migration. It affects the arrangement of the particles flowing through the channel and the structures that the particles form as a result of the flow. Flows of concentrated suspensions in narrow channels occur in several novel technological applications, including semi-solid flow batteries and concentrated nanoparticle inks for 3D printing. This project will investigate the effects of attractive forces between the particles. Preliminary data show that interparticle attractions can suppress shear-induced migration. A series of experiments will be conducted to determine whether attractive forces between particles give rise to transient clusters or aggregates of particles that reduce migration, which could provide a way to better tailor particulate materials for specific applications of interest.
Experiments will quantify effects of interparticle attraction on shear-induced migration and will correlate suspension microstructure with the extent of shear-induced migration. The interparticle attraction will be achieved by adding small amounts of polymer to suspensions of hard spheres to create a depletion force between particles. The effects of attraction range and strength, colloid volume fraction, and flow rate on shear-induced migration and the structure of the resulting suspension will be measured. Deviations from phenomenological models for shear-induced migration that involve only hard sphere interactions will be determined. Suspension microstructure will be correlated with the extent of shear-induced migration by using 3-D confocal imaging and tracking to measure particle distribution functions, cluster sizes, and velocity fluctuations during flow. Effects of boundary conditions at channel walls will also be investigated by chemically modifying the walls to change their surface energy.
