Elaboration of thin colloidal silica films with controlled thickness and wettability

Silica films with controlled thickness and wettability have been formed by sequential adsorption of colloidal silica nanoparticles and a cationic polyelectrolyte (poly(allylamine hydrochloride) or poly(diallyldimethylammonium chloride)) was used as the binding agent. Whatever be the conditions used, the structure of films appeared dense and non-porous. Thicknesses varying from 12 to 430 nm and wettability varying from 5 to 60° were obtained when the pH or concentration of the silica solution was varied. Quartz crystal microbalance measurements evidenced the formation of regular and reproducible thin films mainly composed of silica nanoparticles. These films contained few polycations due to the formation of long-distance charge pairs between silica nanoparticles and polycations.