Controlling bilayer composition and surface wettability of sequentially adsorbed multilayers of weak polyelectrolytes

Variations in the linear charge density of a weak polyacid brought about by controlling solution pH in a layer-by-layer sequential adsorption process were used to systematically control the layer thickness, level of layer interpenetration, and surface wettability of sequentially adsorbed layers of poly(acrylic acid) (PAA) and poly(allylamine) (PAH). The thickness contributed by an individual polyion layer was found to depend primarily on the pH of the polymer's dipping solution and, within the pH range examined, was not influenced by the thickness or level of interpenetration of the previously adsorbed layer. Contact angle and methylene blue adsorption measurements revealed that the deposited layers are typically highly interpenetrated and that the deposition process is a surface charge dominated adsorption process. Using this simple molecular-level blending approach, it is possible to create surfaces with advancing water contact angles that vary from essentially zero (completely wettable surfaces) to as high as 50°, all using the same simple polycation/polyanion combination.