Interactions Between Particles and Solid Surfaces

摘要

This paper studies interactions of particles and solid surfaces, which play a critical role in determining surface contamination level and cleaning efficiency. In the gas phase, interacting bodies are exerted with van der Waals forces and Coulomb forces. Originating from induction, dispersion, and electron overlap mechanisms, van der Waals forces between neighboring bodies are attractive in general but become repulsive at very short separations. To the first order approximation, the van der Waals forces are pair-wise additive. Coulomb forces arise from interactions between electric moments. In the presence of an external electric field, dielectrics are polarized. Mathematically, this phenomenon can be modeled by image charges. The interactions between real charges and image charges are not pair-wise additive. For systems immersed in liquids, the solvent-induced interactions are determined by the Gibbs free energy changes. Electric double layers are formed between the particles and the contact surface immersed in aqueous media where ionic species are present. The electrostatic forces are measured by the zeta potentials. Capillary forces are caused by thin liquid layer between the particle and surface and are directly proportional to the surface tension of the film and the interfacial area. At the thermodynamic equilibrium, particles experience thermal motion around the potential well and escape from the region if the removal forces are sufficiently large. There are two main categories of removal forces: vibration or other mechanical motion, which causes a change in the velocity of the particle relative to the surface, and drag on the particle by a moving fluid.