DIFFUSIONAL DEPOSITION OF CHARGED LATEX-PARTICLES ON WATER-SOLID INTERFACES AT LOW IONIC-STRENGTH

The deposition of positively charged latex particles with radii betwee n 20 and 100 nm on a negatively charged mica surface is investigated w ith atomic force microscopy at low ionic strengths. The polystyrene la tex spheres with amidine headgroups are characterized as to their size distribution, electrophoretic mobility, and aggregation behavior. Sur face coverage measurements take into account the polydispersity of the particles on the surface. Deposition kinetics from a quiescent soluti on are, for low coverage, in good agreement with diffusion-limited ads orption. At long times, the surface coverage tends toward a maximum su rface coverage theta(max) independent of the particle concentration bu t depending on ionic strength. This work extends the available data fo r theta(max) for small particle size and very low ionic strengths. The values for theta(max) decrease with decreasing ionic strength; this t rend is described with a simple model based on random sequential adsor ption and the effect of overlapping double layers. Particle size polyd ispersity can modify the results for theta(max) substantially; its inf luence is investigated in detail.