Stability of colloidal clusters in shear flow near a wall: Stokesian dynamics simulation studies

An earlier algorithm for Stokesian dynamics simulation of colloid particles in a fluid bounded by a hard wall is extended to the case when a linear sh ear flow is applied. The algorithm includes many-body hydrodynamic interact ions arising from the shear flow with lubrication corrections for pairs of close particles. The extended algorithm is used to simulate small clusters of particles which may interact with each other and with the bounding wall through model potentials with repulsive cores and attractive tails. The pai r problem is studied first, in bounded and unbounded fluid, both with and w ithout pair and wall interactions. The critical shear rate necessary to bre ak a bound pair is determined for a range of initial configurations. Wherea s in unbounded fluid a bound pair rotates with the vorticity of the shear f low, near a wall the hydrodynamic forces introduce a new breakup mechanism in which the pair tilts through a finite angle relative to the wall before separating. This tilt mechanism requires significantly stronger shear field s than are needed to separate a pair in unbounded fluid. Linear arrays of p articles as well as examples of 2- and 3-D bound clusters are studied next to show how the wall and the tilt mechanism modify the shear-induced breaku p. With a wall potential included, significant changes are seen in the fina l distribution of particles resulting from cluster breakup. (C) 2001 Americ an Institute of Physics.