Characteristics of polyelectrolyte multilayers: The effect of polyion charge on thickness and wetting properties

Polyelectrolyte (PE) multilayer films are surface structures obtained by sequential adsorption of oppositely charged polymers. In the present work we focused on the influence of pH of the solutions of strong and weak polyelectrolytes on the thickness and wetting of multilayers formed on silicon wafers. Four types of PE were used: polyallamine hydrochloride (PAH), poly(diallyldimethylammonium)chloride (PDADMAC), poly(acrylic acid) (PAA), polysodium 4-styrenesulfonate (PSS). Thickness of PE films was measured by ellipsometry and their wetting properties were determined by contact angle measurements. Thicker films were found in conditions when the polyelectrolytes were weakly charged. We observed periodic, layer-to-layer oscillations of contact angle values with the amplitude dependent on type of PE pair and conditions of film formation, however, films with a polycation as the top layer were more hydrophobic.