Deposition, Equilibrium Structure and Mechanical Response of Polyelectrolyte Complexes

Deposition, Equilibrium Structure and Mechanical Response of Polyelectrolyte Complexes Summary Polyelectrolyte complexes formed by the interaction of oppositely charged macromolecules are an important class of soft, polymeric material. These materials are of interest largely because of their mechanical properties, which can span the full spectrum of behaviors from low-viscosity liquids to brittle solids. The aim of this project is the factors that control this behavior, using well-characterized model systems. Intellectual Merit The focus of the project is on polyelectrolyte complexes in thin film form, both because of the utility of these materials as surface modifiers, and because the thin film geometry is particulalry convenient for the proposed investigations. There are three aspects of these investigations, beginning with new deposition mechanisms based on the electrochemical control of the pH at the electrode surface. The second set of experiments is aimed at mapping out the phase behavior. The third element of the proposed program is the most extensive, and involves mechanical characterization of the polyelectrolyte complex films. Acoustic methods will be used to characterize the linear viscoelastic properties of these materials on a time-scale of ≈ 60 nanoseconds, approaching the timescale that is accessible by molecular dynamics simulations, bridging the gap between experiment and computational modeling. In addition, the nonlinear properties of these materials will be investigating using creep and fracture experiments designed specifically for investigation of thin films in the hydrated state. Broader Impacts The development of materials able to respond in controlled ways to high concentrations of added salt are useful in applications in water purification, where system performance is limited by fouling of the membrane surfaces. Polyelectrolyte complex film represent a potential solution to this problem. In addition, further development of the high frequency rheometric technique will make this method much more accessible as a standard characterization method.