The deposition of positively charged latex particles with radii between 20 and 100 nm on a negatively charged mica surface is investigated with atomic force microscopy at low ionic strengths. The polystyrene latex spheres with amidine headgroups are characterized as to their size distribution, electrophoretic mobility, and aggregation behavior. Surface coverage measurements take into account the polydispersity of the particles on the surface. Deposition kinetics from a quiescent solution are, for low coverage, in good agreement with diffusion-limited adsorption. At long times, the surface coverage tends toward a maximum surface coverage θmax independent of the particle concentration but depending on ionic strength. This work extends the available data for θmax for small particle size and very low ionic strengths. The values for θmax decrease with decreasing ionic strength; this trend is described with a simple model based on random sequential adsorption and the effect of overlapping double layers. Particle size polydispersity can modify the results for θmax substantially; its influence is investigated in detail.

No abstract

No abstract

No abstract

No abstract

For stratified layers, it was recently demonstrated that information about the structure of thin dielectric layers could be determined from scanning angle reflectometry measurements independent of any model of the interface. A measure of the deviation of the film from uniform was defined and demonstrated to be measurable. This analysis is extended here to the case of particulate layers, where we show that the same uniformity parameter can give information about the deviation of the distribution of particles on the surface from a uniform one. Preliminary optical data on moderately sized polystyrene particles, 116 nm in diameter, suggest that the closest approach of two particles on the surface is considerably greater than their diameter. This is in agreement with direct measurements of the radial distribution functions of these particles adsorbed on surfaces under similar conditions.

No abstract

No abstract