Colloid particle deposition on heterogeneous surfaces produced by polyelectrolyte adsorption

The kinetics of polystyrene latex deposition on mica surface covered by mono- and bilayers of polyelectrolytes has been studied using the optical microscopy and the AFM methods. In these investigations the cationic poly(ethylene imine) (PEI) having an averaged molecular weight of 70 kD was used and the anionic poly(acrylic acid) (PAA) having a linear structure and an average molecular weights of 12 and 70 kD. Formation and stability of polyelectrolyte layers on mica was characterized in terms of streaming potential measurements carried out using a parallel-plate channel arrangement. These polyelectrolyte layers have been exploited as substrates of controlled heterogeneity and charge density for deposition of colloid particles. Positively charged polystyrene latex particles having an average size of 450 nm (determined by laser diffractometry, PCS and AFM) were used in these experiments. Latex deposition kinetics was studied under convection-controlled transport conditions using the impinging-jet cell and the optical microscopy method. The AFM method was also used to confirm maximum coverage of latex particles. The dependence of the initial deposition rate of particles on the coverage of PAA in the PEI/PAA bilayer was systematically studied. It was found that the initial deposition rate increased monotonically with the density of the adsorbed polyelectrolyte layer. These experimental results, deviating from the DLVO theory predictions, were successfully interpreted in terms of a theoretical model, which considered charge fluctuations within the adsorbed polyelectrolyte layers. It was concluded that the particle deposition method can be applied as a sensitive tool for quantitatively determining the presence of polyelectrolyte layers on solid surfaces, at a coverage degree inaccessible for other methods.