Effects of surface roughness on van der Waals and electrostatic contributions to particle-particle interactions and particle adhesion

A computational model is described for calculating the van der Waals and electrostatic interaction energies between charged particles of arbitrary surface roughness. The model is valid at all separation distances and could thus be used to predict the contributions of these two forces to the total force of adhesion between a particle and substrate. The van der Waals interaction was calculated using the Hamaker pairwise additivity approach in which the intermolecular interaction is integrated over all molecular pairs. The electrostatic interaction was calculated using a boundary element approach in which the surfaces of both interacting particles were discretized into a set of flat triangular elements. The linearized Poisson-Boltzmarm equation was then solved for this system under the condition of either constant surface charge density or constant surface potential. Results from typical types of roughness (i.e., bumps, pits and waves) are presented and discussed. It was found that for the interaction between two spherical particles, the presence of bumps on one of the particles with height equal to 0.1 times the particle radius reduced the magnitude of the energy barrier to particle contact by approximately 13%.