Brownian deposition kinetics of latex particles onto glass and polystyrene

There has been a large body of work on the deposition of colloidal particles onto many different kinds and shapes of surfaces. Nearly all work in the past has involved flowing systems in which a well-defined hydrodynamic layer exists at the collector surface with certain advantages and disadvantages. We have chosen a still system in which transport of particles to the collector surface occurs solely by diffusion. Both particles and surfaces were negatively charged, so that deposition was driven by dispersion forces. A photomicroscopic technique has been used to determine absolute values of initial rates of deposition. Three monodisperse polystyrene colloids of various particle sizes and surface charge densities were synthesized. Their zeta potentials were determined by microelectrophoresis in Ba(NO 3 ) 2 solutions. Collector surfaces were glass and glass coated with polystyrene. Their zeta potentials were determined from their streaming potentials in various concentrations of electrolyte. Direct determination of diffusion coefficients indicate that the particles behave normally. Initial deposition rates exhibit strong dependence on ionic strength, indicating large electrical double layer effects. Like the work of others, rates of deposition fell off with time, perhaps due to the presence of `hot spots', i.e. highly localized areas of greater reactivity. The most regular behavior occurred in deposition on polystyrene-coated glass, presumably because roughness and highly reactive sites on the glass surface were largely eliminated. Absolute rates were several times theoretical for fastest deposition. It is speculated that the hydrophobic effect plays a significant role in accelerating particles towards the collector. Plots of log (initial rate constant) vs. log (ionic strength) were linear and generally in the order anticipated by Reerink–Overbeek theory.