  We have shown [J.\ Fluid Mech.\ {\bf 592}, 447 (2007)] that swapping
(reversing) trajectories in confined suspension flows prevent collisions
between particles approaching each other in adjacent streamlines. Here we
demonstrate that by inducing layering this hydrodynamic mechanism changes the
microstructure of suspensions in a confined Couette flow. Layers occur either
in the near-wall regions or span the whole channel width, depending on the
strength of the swapping-trajectory effect. While our theory focuses on dilute
suspensions, we postulate that this new hydrodynamic mechanism controls
formation of a layered microstructure in such flows in a wide range of
densities.
