This research is directed at establishing the conditions for the adsorption/desorption phase transition for polyelectrolytes at the solid/solution interface. A primary goal is to provide a comprehensive set of data to examine some of the extensive theoretical work on polyelectrolyte adsorption, which has not yet been fully tested, and to stimulate further development of theory. Guided by recent theory, the effect on the adsorption transition of variables such as the surface charge, polymer charge, supporting electrolyte concentration, temperature and molecular weight will be examined in detail. The principal means of regulating the surface charge will be through in situ potentiostatic control of the electrical double-layer. Care will be taken to produce surfaces with well-defined morphology so that the theory may be tested with confidence. The thickness of adsorbed polymer films, as well as the mode of attachment of polyelectrolyte molecules, will be examined by ellipsometry and surface enhanced Raman scattering, respectively. Novel applications of techniques such as the quartz crystal microbalance and infrared reflectance will be undertaken to probe phase transitions in these two-dimensional systems. Competitive adsorption studies using charged and neutral polymers will reveal the relative importance of coulombic and non-coulombic surface/polymer interactions. This research could potentially lead to advances in electronic materials, biomolecular materials, and improvements in flocculants for water purification.
