Controlling the physicochemical properties of weak polyelectrolyte multilayer films through acid/base equilibria*

Multilayer thin films prepared from weak polyelectrolytes can exhibit a rich suite of anomalous physicochemical properties. One of the major factors that influence the properties of such films is the acid/base chemistry of the weak functional groups of the polyelectrolytes. In fact, the apparent dissociation constants of weak polyelectrolytes can shift by as much as 1–4 pH units upon incorporation into multilayer films from that in dilute solution. Here, we discuss this variability in the dissociation behavior of polyelectrolytes in multilayer films, and how it relates to understanding the diversity in the physicochemical properties observed for films assembled from the same polyelectrolytes, but under different pH conditions. In turn, we review some of the recent research that attempts to take advantage of the pH-tunable properties of multilayer films for a variety of applications.