Approaching the precipitation temperature of the deposition solution and the effects on the internal order of polyelectrolyte multilayers

Polyelectrolyte multilayers are prepared by consecutively adsorbing poly(allylamine hydrochloride) (PAH) and poly(styrene sulfonate) (PSS) from aqueous KCI solution (1 mol/L) at different temperatures, approaching the precipitation temperature at 55 degrees C. The films are characterized by X-ray and neutron reflectometry, using selectively deuterated PSS layers. When the preparation solution is heated, the film thickness increases up to 75% the film/air and the internal roughness increase by up to a factor of 3. Below 35 degrees C preparation temperature, the internal roughness is about 40% of the thickness of a polycation/polyanion layer pair, the same result as obtained when the bilayer thickness is controlled by varying the salt content in the deposition solution. At higher preparation temperatures, the interpenetration is more pronounced, a feature which may be attributed to the theoretically predicted changes of the polymer conformation in solution from extended configuration to pearl-necklace or even globular structures.