Colloid adsorption at heterogeneous surfaces

Irreversible adsorption of colloid particles at heterogeneous surfaces was studied experimentally. The substrate of controlled heterogeneity was produced by covering mica sheets by colloid iron oxide (hematite) particles to a desired concentration. The particles of averaged diameter of 70 nm were produced by forced hydrolysis of FeCls solutions followed by a hydrothermal ageing. The coverage of colloid hematite particles (heterogeneity degree) was determined by electron microscopy and atomic force microscopy (AFM). Adsorption kinetics of polystyrene latex (averaged diameter 0.87Mim) at heterogeneous surfaces was studied by using the direct optical microscope observations in the impinging-jet cell. It was demonstrated that the initial adsorption rate attained the limiting value pertinent to homogeneous surfaces for heterogeneity degree of a few per cent. 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 random sequential adsorption (RSA) model.