Influence of Adsorption Conditions on the Structure of Polyelectrolyte Multilayers

Polyelectrolyte adsorption onto an oppositely charged interface is determined by electrostatic and secondary interactions. Since polyelectrolytes precipitate at elevated temperatures, the secondary interactions are presumably temperature dependent. This idea is tested for poly(allylamine) hydrochloride/polystyrene sulfonate (PAH/PSS) films adsorbed from aqueous KCl solution (high salt conditions) at temperatures between 5 and 40 °C. KCl was chosen because the films were thicker than those obtained from NaCl or CsCl solutions indicating strong specific binding between K and PSS. The film thickness increases continuously with the adsorption temperature; the changes amount to 20−40%, depending on salt conditions. Furthermore, the roughness is increased, up to a factor of 5. The latter is attributed to the decreased percentage of strong electrostatic bonds within the polyelectrolyte multilayer. Another path to increased roughening is using low-weight polymers with a contour length similar to the thickness of a polycation/polyanion pair.