Percolation of sheared suspensions of attractive hard spheres

We have simulated suspensions of colloidal spheres under shear flow to study the formation of clusters, the percolation transition, and the conductivity of the suspensions. The spheres interact via a steep repulsive core and an optional attractive tail of varying strength. In the steady state, we observe transient clusters in the plane orthogonal to the flow direction, which lead to a decreased percolation threshold. These anisotropic clusters are strongly aligned. They affect the conductivity under shear and occur independently of the geometric connectivity criterion and the attractive strength of the spheres. Attractions lower the percolation threshold, but shear flow counteracts this effect. The alignment of clusters and the anisotropy of the conductivity become non-monotonic for the strongest attraction we studied. The flow-aligned orientation of clusters controls the behavior at weaker shear in that case.