Nanoporous thin films formed by salt-induced structural changes in multilayers of poly(acrylic acid) and poly(allylamine)

Abstract

We report here on the influence of changes in the solution salt concentration on the structure of multilayers of weak polyelectrolytes. For poly(acrylic acid) (PAA) and poly(allylamine) (PAH) multilayers assembled by the layer-by-layer process in the presence of sodium chloride, washing with pure water after deposition of each layer produces films with considerable surface roughness (root-mean-squared (rms) roughness ∼ 17 nm for a 10 layer film), as assessed by scanning force microscopy. In contrast, relatively smooth (rms roughness ∼1 nm) and homogeneous PAH/PAA multilayer films are formed when the salt concentration is kept constant both during the assembly process and in the washing steps..