| Adsorbed polymeric surfactants provide a flexible, powerful route towards engineered material surfaces. Molecules of this sort have been used, for example, in the stabilization of colloidal suspensions, the development of selective filtration systems, and the design of surfaces with specific biocompatibility requirements. While neutral polymers have received much attention experimentally, their low solubility in water makes them suitable for use only in organic solvents. My research has aimed to bring a similar level of quantitative understanding to the adsorption of water soluble, charged polymeric surfactants. Unlike their neutral analogues, the behavior of charged polymers is complicated by the presence of long-ranged electrostatic interactions, which has important implications for their adsorption.; Using phase-modulated ellipsometry, I have monitored in situ the adsorption of two classes of hydrophobic/ionic diblock copolymer surfactants from aqueous solutions to identify the key parameters that govern their adsorption kinetics. The two systems studied were poly(t-butyl styrene)-block-poly(styrene sulfonate) (PtBS-b-PSS) and polystyrene-block-poly(acrylic acid) (PS-b-PAA). PSS is a polyacid with a fixed degree of ionization and PAA is a polyacid whose degree of ionization is controlled by the solution pH. In both systems, the polyacid is tethered to the surface by the insoluble neutral block.; This research has delineated the mechanisms by which these two charged polymeric surfactants adsorb, with special emphasis on the influence of electrostatic interactions, the effect of solution micellization, and the role of surface hydrophobicity. These studies help form a framework in which to understand the adsorption of charged polymeric surfactants, providing a basis for predictable materials engineering of interfaces in aqueous environments. |
