Influence of Charge Density and Ionic Strength on the Multilayer Formation of Strong Polyelectrolytes

The influence of ionic strength and polymer charge density on the multilayer formation of strong polyelectrolytes is investigated by X-ray reflectivity. To a first approximation the adsorption behavior as a function of the degree of charge, f, is binary: For f ≤ 50% the films are one order of magnitude thinner than those for f ≥ 75%. This is due to a threshold of charge overcompensation after each adsorption step which seems to be at f between 50% and 75%. Above the charge reversal limit the thickness and the surface roughness increase with decreasing polymer charge. Below a charge density of 50% the film thickness cannot be changed by salt additive whereas the film thickness increases with cNaCl1/2 above a degree of charge of 75%. The density of all investigated films is quite similar.