Preparation, characterization, and application of pH-responsive polyelectrolyte multilayer films

This dissertation focuses on learning how to control the physico-chemical properties of multilayer thin films containing weak polyelectrolytes by gaining an understanding of the films from a fundamental perspective. This information is then used, as a proof of principle concept, to assemble films with desired properties for a model application. Multilayer thin films were prepared using the layer-by-layer deposition technique, which involves the sequential adsorption of oppositely charged polymers onto a charged substrate from dilute aqueous solutions. The charge density of weak polyelectrolytes is highly sensitive to the pH and ionic strength of the solution environment. In turn, the solution behavior of such polymers influences their properties when adsorbed on a surface. An extensive investigation of the acid-base equilibria of the polyelectrolytes polyallylamine hydrochloride and poly(acrylic acid) upon incorporation into the film was carried out and the result compared to the dissociation behavior of these polymers in dilute solution.The study of the acid-base chemistry in weak polyelectrolyte multilayer films was extended to a more complex biopolymer combination of poly(L-lysine) and hyaluronic acid. These polymers are able to adopt secondary conformational ordering in the form of alpha-helices and beta-sheets. The acid-base equilibria of the polyelectrolytes were investigated as a function of solution pH and the total number of layers in the film. These results were correlated with those obtained from the study of some of the surface and bulk properties of the films such as surface wettability, friction, film thickness, and the degree of film swelling.The extent to which polymer films can swell depends on both the properties of the film matrix and the swelling medium. The hydration of polyelectrolyte multilayer films is of importance in the potential applications of the films. This promoted an investigation of the effect of the assembly conditions (i.e. solution pH and the total number of layers assembled), and properties of the swelling medium such as pH and ionic strength on the overall swelling of polyallylamine/hyaluronic acid multilayer films. In turn, this information was used, in part, to understand the pH-dependent loading and release behavior of small hydrophilic molecules in the films as a model application for polyelectrolyte multilayer assemblies