Direct investigation of anisotropic suspension structure in pressure-driven flow

Evidence is presented to show the microstructural anisotropy responsible for normal stress in sheared suspensions. Particle velocimetry is combined with three-dimensional particle locations obtained via confocal microscopy at rest. A range of volume fractions phi and local shear rates (gamma) over dot are investigated in a weakly Brownian pressure-driven suspension. At high (gamma) over dot, the pairwise distribution shows a strong probability along the axis of compression similar to observations from Stokesian dynamics simulation at phi = 0.32. At the channel center where (gamma) over dot -> 0, the concentrated suspension at phi = 0.56 behaves as a confined isotropic fluid.