Characterization of new surface morphologies in a hydrogen-bonded multilayer system

Abstract

This work presents an analysis of surface morphology changes in poly(acrylic acid)/polyacrylamide (PAA/PAAm) hydrogen-bonded multilayers. These changes were induced by immersion of the films in aqueous solutions of poly(allylamine hydrochloride), or PAH, at different levels of pH. Positive charges on PAH are attracted to negative charges on PAA, forming ionic bonds and locally decreasing the hydrophilicity of the multilayer. The degree of ionization for each polyelectrolyte, controlled by the pH of the treatment solution, determines the molecular conformations and the extent of electrostatic interactions. These factors, in turn, determine the resulting morphology of the film. Different surface morphologies appeared in four different pH regimes. Highly acidic solutions retained the film's original smooth surface, but wrinkled, honeycomb, or globular morphologies appeared as the pH increased. The three different surface morphologies correlate with the linear, pearl necklace, and globular conformations of PAH.