The Role of Surface Roughness and Contact Deformation on the Hydrodynamic Detachment of Particles From Surfaces

The effects of elastic deformation and surface roughness on the hydrodynamic detachment of colloidal particles from surfaces have been studied. Experimental results for glass and polystyrene particles on glass and mica substrates are reported. A theoretical model is developed using a Green's function formulation to explain the origin of the restraining torque acting on the particle. Two limiting situations are analyzed: (a) rigid sphere on a deformable substrate and, (b) deformable sphere on a rigid substrate. It is concluded that surface roughness is a necessary condition to account for the observed critical hydrodynamic force. The magnitude of this critical force has been found to depend on three competing factors: particle roughness, roughness of the substrate, and the extent of contact deformation.