pH-Dependent Thickness Behavior of Sequentially Adsorbed Layers of Weak Polyelectrolytes

A detailed study of the role that solution pH plays in the layer-by-layer processing of the weak polyelectrolytes poly(acrylic acid) and poly(allylamine hydrochoride) was carried out. It was found that dramatically different polymer adsorption behavior is observed as one systematically increases (or decreases) the charge density of a weak polyelectrolyte including transitions from very thick adsorbed layers (ca. 80 Å) to very thin adsorbed layers (ca. 4 Å) over a very narrow pH range. By controlling pH, it is possible to vary the thickness of an adsorbed polycation or polyanion layer from 5 to 80 Å. In addition, control over the bulk and surface composition of the resultant multilayer thin films is readily achieved via simple pH adjustments. These studies have provided new insights into the polyelectrolyte sequential adsorption process and have already opened up some interesting technological applications.