Role of convection in particle deposition at solid surfaces

Abstract

Recent theoretical and experimental data concerning colloid particle deposition from well-defined flows onto solid/liquid interfaces were reviewed. The macroscopic flow fields in the vicinity of the spherical and cylindrical collector (both isolated and forming a structured layer) were presented. Analogous solutions for the impinging-jet cells of (i) radial symmetry (radial impinging-jet cell RIJ) and (ii) plane symmetry (the slot impinging-jet cell SIJ) were also discussed. Similarities and differences between these flows are pointed out. The method of decomposing the macroscopic flows into local flows of simple geometry like shearing and stagnation flows was exposed. The microscopic flows are discussed in some detail, especially those connected with the motion of a spherical particle parallel and perpendicular to a solid wall. Using the local flow distributions the governing continuity equation is formulated, incorporating the convective transport in the bulk and the specific force dominated transport at the surface. Approximate analytical models aimed at decoupling these transfer steps are described, in particular the surface force boundary layer approximation (SFBLA). Limiting analytical solutions for the perfect sink boundary conditions were given. A procedure of extending the convective diffusion theory to non-linear adsorption regimes governed by the steric barrier due to adsorbed particles, was also presented. The role of the electro-hydrodynamic coupling leading to the hydrodynamic scattering effect in the blocking phenomena was discussed. The theoretical results are confronted with experimental data obtained in the well-defined systems, e.g. mostly in the RIJ and SIJ cells using monodisperse polystyrene latex colloids. A good agreement of theoretical and experimental data was found and most of the theoretical predictions were quantitatively confirmed, in particular the significance of the hydrodynamic scattering effect.