Early steps of the film growth mechanism in self-assembled multilayers of PAH and PSS on silica: Polymer uptake, charge balance and AFM analysis

This study investigates the growth of self-assembled polyelectrolyte films with strong polyacid (poly(styrene sulfonate), PSS and a weak polybase (poly(allylamine hydrochloride), PAH at pH 9. Addressing the deposit of the first 3 bilayers, we focus on the successive adsorption isotherms, the effect of maintaining a constant pH, the charge balance and the counterions co-adsorption in the successive steps. We also present stepwise AFM images of the film grown on a silica wafer, showing a very heterogeneous morphology with bumps and valleys, totally unlike the expected regular superposition of bi-dimensional polymer layers. Finally, a sketch of the growth mechanism is proposed, featuring most of the experimental observations in the study.