Fundamental Energetics and Transmembrane Nanostructuring in Polyelectrolyte Membranes

Florida State University, Tallahassee FL

Investigators

Abstract

Complexed polyelectrolytes, including those formed into ultrathin films by the "multilayering" technique, present a fascinating phase of soft condensed matter. Structurally diffuse, polyeclectrolyte multilayers offer unparalleled compositional flexibility and a host of promising applications. This proposal seeks to address the single most important quantitative descriptor of polyelectrolyte multilayers and complexes: the equilibrium constant characterizing swelling by salt. Swelling plays a pivotal role in the growth of multilayers, their transport properties when used as membranes, their stability and this use in processing, micropatterning and cell adhesion promoters. In a novel approach, swelling constants will be evaluated for different combinations of polyelectrolytes to arrive at a characteristic free energy of ion pairing for a single polyelectrolyte segment. The "interaction energy" may be used to predict the swelling performance, and properties flowing therefrom, of any combination of polyelectrolytes, whether in ultrathin films or other morphologies. Coupled with this foray into fundamental polymer physical chemistry, and in the spirit of nano-biotechnology, new methods for introducing selective nanostructured ion channels, ordered and oriented by hydrophobicity gradients, will be developed. The proposed ion conducting polypeptide, designed to run perpendicular to the surface, will literally open up a third dimension for nanostructuring multilayers. The multilayering of polyelectrolytes and other charged nanoscopic species is an enabling technology. A potent combination of undemanding equipment requirents and functional and compositional possibilities has stimulated interdisciplinary research and education. The impact of multilayers on technology is already evidenced by a broad range of proposed and realized applications in diverse fields such as nanostructuring, biotechnology, drug release and surface modification. This two-part proposal offers dual paradigms: one, a fundamental unifying concept in a rapidly expanding field, the other, a new paradigm in structure and structuring. The proposed work, whose logistics are underpinned by easily digested concepts, will have the broadest possible impact on the field by tracking down and making available the equilibrium constants which represent the essence of the physical chemistry of multilayers and polyelectrolyte complexes in general. Rationalization and prediction of the properties of polyelectrolyte complexes, materials with a venerable history, will assist them in entering the realm and lexicon of technologically useful molecular building blocks. The use of hydrophobicity gradients to direct nanostructure assembly provides for interlayer communication when multilayers are used to fabricate compartmentalized hierarchical structures, an emerging science.