(367e) Direct Measurement of Suspension Microstructure: Effects of Combined Hydrodynamic Electrostatic, and Viscoelastic Interactions

Microstructure is key to understanding rheological behaviors of flowing particulate suspensions. Previous results obtained numerically via Stokesian Dynamics reveal an anisotropic structure forming under high Peclet number conditions. This work outlines an experimental technique based on confocal microscopy to study microstructure of a colloidal suspension in an index-matched fluid flowing in a microchannel. Results of simulation-like quality are produced and the effect of Pe and interparticle force is investigated. Microstructure is shown to be consequential from competitions between hydrodynamic, thermal, electrostatic, and elastic forces depending on the suspending medium.  In highly screened systems, the stress of suspension calculated based on the microstructural information is compared with previous computations.  In systems where screening is reduced and the Debye length is significiant, the particles interact both through soft repulsion and hydrodynamic interactions, relaxing the structure observed in systems having pure hydrodynamic interactions.  We also explore non-Newtonian suspending fluids, such as Boger fluids, to gauge the effect of elasticity on suspension structure.