the deposition of latex particles on to a glass plate using A set of analytical equations are developed for calculating the the rotating disc apparatus, which was attributed to surface van der Waals and electrostatic interaction energies between a roughness. Kihira et al. (3) studied the coagulation kinetics rough spherical particle and a smooth plate. The particle of polystyrene lattices, silica and cerium oxide particles as roughness is modeled as hemispherical asperities of fixed radius, a function of ionic strength. The authors found a discrepancy in agreement with SEM micrographs of polystyrene latex spheres.
between the measured and theoretically predicted values of
The van der Waals energy is calculated using a pairwise summathe stability ratio which, for the cerium oxide particles, was tion technique for both nonretarded and retarded cases. The elecattributed to surface roughness. By varying the radius of trostatic energy is calculated using the linear superposition apcurvature of the roughness elements, the authors obtained a proximation and assuming the asperity-plate and particle-plate interactions are additive. We find that at large separations, the good fit with experiment. Tobiason (4) studied the deposiincreased electrostatic repulsion produced by the roughness results tion of non-Brownian latex particles in beds of glass beads. in a shallower secondary potential well. At closer separations, Particle deposition was observed for conditions where theohowever, the increased van der Waals attraction produces a draretically no deposition should occur, and surface roughness matically lower repulsive barrier (as much as two orders of magniwas considered as a possible cause.
tude smaller in the example presented). This lower barrier would
Numerous authors have developed models for predicting yield much larger capture rates than predicted by DLVO theory the interaction forces between rough surfaces. Czarnecki and for smooth surfaces, in qualitative agreement with experimental Dabros (5) evaluated the van der Waals interaction between observations.