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 $\varphi$ and local shear rates $\dot{\gamma }$ are investigated in a weakly Brownian pressure-driven suspension. At high $\dot{\gamma }$, the pairwise distribution shows a strong probability along the axis of compression similar to observations from Stokesian dynamics simulation at $\varphi =0.32$. At the channel center where $\dot{\gamma }\to 0$, the concentrated suspension at $\varphi =0.56$ behaves as a confined isotropic fluid.

• Received 20 July 2009

DOI:https://doi.org/10.1103/PhysRevE.81.041403