| This dissertation is aimed at understanding the important factors which influence the processes of colloid adhesion and detachment from a substrate by a liquid in simple laminar flow.;Particle detachment experiments were conducted to measure the critical hydrodynamic force required to detach non-Brownian colloidal particles from a flat substrate. The influence of several variables such as particle size, surface properties of both the particle and the substrate, their elastic properties, gravity, as well as the physical and electrochemical properties of the intervening fluid medium has been studied. In aqueous solvents the results of these experiments have been found to be in accordance with the predictions the classical DLVO theory of colloid stability.;It has been shown that particle detachment occurs by rolling rather than by sliding or lifting. A rigorous theoretical analysis is presented to conclusively show that the origin of resistance to particle rolling is due to the presence of surface roughness. The magnitude of this restraining torque depends on the relative extent of surface roughness of the particle and the substrate, their elastic properties, and the magnitude of surface forces.;Experiments were conducted to directly measure the pull-off force required to detach colloidal particles from a substrate using an Atomic Force Microscope (AFM). Most of these results show trends similar to those obtained in the hydrodynamic detachment experiments. The instability associated with the AFM cantilever spring, however, presents some limitations in providing a consistent interpretation of these results.;A new Molecular Dynamics (MD) simulation technique was developed to calculate the structural forces in confined molecular fluids using a linear superposition approximation. By calculating the chemical potential as a function of separation distance the approximation has been shown to be valid for separations down to about two molecular diameters. Both the density profiles and solvation force isotherms are oscillatory in nature having periodicity of about one molecular diameter. The oscillations in structural force decay approximately exponentially with separation distance. It is found that structural forces play a dominant role in interactions between two solid surfaces in non-aqueous solvents. |
