Brownian deposition kinetics of latex particles onto glass and polystyrene

There has been a large body of work on the deposition of colloidal particle s onto many different kinds and shapes of surfaces. Nearly all work in the past has involved flowing systems in which a well-defined hydrodynamic laye r exists at the collector surface with certain advantages and disadvantages . We have chosen a still system in which transport of particles to the coll ector surface occurs solely by diffusion. Both particles and surfaces were negatively charged, so that deposition was driven by dispersion forces. A p hotomicroscopic technique has been used to determine absolute values of ini tial rates of deposition. Three monodisperse polystyrene colloids of variou s particle sizes and surface charge densities were synthesized. Their zeta potentials were determined by microelectrophoresis in Ba(NO3)(2) solutions. Collector surfaces were glass and glass coated with polystyrene. Their zet a potentials were determined from their streaming potentials in various con centrations of electrolyte. Direct determination of diffusion coefficients indicate that the particles behave normally. Initial deposition rates exhib it strong dependence on ionic strength, indicating large electrical double layer effects. Like the work of others, rates of deposition fell off with t ime, perhaps due to the presence of 'hot spots', i.e. highly localized area s of greater reactivity. The most regular behavior occurred in deposition o n polystyrene-coated glass, presumably because roughness and highly reactiv e sites on the glass surface were largely eliminated. Absolute rates were s everal times theoretical for fastest deposition. It is speculated that the hydrophobic effect plays a significant role in accelerating particles towar ds the collector. Plots of log (initial rate constant) vs. log (ionic stren gth) were linear and generally in the order anticipated by Reerink-Overbeek theory. (C) 1999 Elsevier Science B.V. All rights reserved.