Low Reynolds number interactions between colloidal particles near the entrance to a cylindrical pore

The interaction between stable colloidal particles arriving at a pore entra nce was studied using a numerical method for the case where the particle si ze is smaller than but of the same order as the pore size. The numerical me thod was adapted from a front-tracking technique developed for studying inc ompressible, multifluid flow by S. O. Unverdi and G. Tryggvason (J. Comp. P hys. 100, 25, 1992). The method is based on the finite difference solution of Navier-Stokes equation on a stationary, structured, Cartesian grid and t he explicit representation of the particle-liquid interface using an unstru ctured grid that moves through the stationary grid. The simulations are in two dimensions, considering both deformable and nondeformable particles, an d include interparticle colloidal interactions. The interparticle and parti cle-pore hydrodynamic interactions, which are very difficult to determine u sing existing analytical and semi-numerical, semi-analytical techniques in microhydrodynamics, are naturally accounted for in our numerical method and need not be explicity determined. Two- and three-particle motion toward a pore has been considered in our simulations. The simulations demonstrate ho w the competition between hydrodynamic forces and colloidal forces acting o n particles dictate their flow behavior near the pore entrance. The predict ed dependence of the particle flow behavior on the flow velocity and the ra tio of pore size to particle size are qualitatively consistent with the exp erimental observations of V. Ramachandran and H. S. Fogler (J. Fluid Mech. 385, 129, 1999). (C) 2000 Academic Press.