Particle deposition at electrostatically heterogeneous surfaces

Irreversible adsorption of negatively charged polystyrene latex particles (averaged diameter 0.9 μm) at heterogeneous surfaces was studied experimentally. The substrate of controlled heterogeneity was produced by covering freshly cleaved mica sheets by positively charged polystyrene latex (averaged diameter of 0.47 μm) to a desired surface coverage. Positive latex deposition was carried out under convection and diffusion-controlled transport conditions and the coverage (defined as heterogeneity degree) was determined by direct particle counting using the optical and electron microscopy. Deposition kinetics of larger latex particles at heterogeneous surfaces produced in this way was studied by using the direct optical microscope observations in the impinging-jet and diffusion cells. It was demonstrated that the initial adsorption rate under the convection-controlled transport attained the limiting value pertinent to homogeneous surfaces for heterogeneity degree of a few per cent. This effect was even more pronounced for diffusion-controlled transport conditions. This behaviour was quantitatively interpreted in terms of the theoretical model considering the coupling between surface and bulk transport of particles. Similarly, the experimental results obtained for higher surface coverage of latex (long adsorption times) were in a good agreement with the generalised random sequential adsorption (RSA) model.