With the support of the Experimental Physical Chemistry Program, Prof. Charles S. Johnson of the University of North Carolina at Chapel Hill will pursue a number of research objectives: 1) he will expand the capabilities of Diffusion Order Nuclear Magnetic Resonance Spectroscopy (DOSY), so that it can be used to study systems with very small diffusion coefficients. This will require very large magnetic field gradients, and Johnson plans on exploiting the large fringe fields of the superconducting magnet for the pulsed field gradient NMR. 2) He plans on measuring molecular weight distributions of fluoropolymers in supercritical carbon dioxide, an environmentally benign solvent; this will require the design of a high pressure instrument. 3) Johnson will develop heteronuclear DOSY, and 4) he will make improvements on electrophoretic NMR techniques using Mobility Ordered 2-dimensional NMR spectroscopy, or MOSY. DOSY and electrophoretic NMR allow the measurement of molecular diffusion coefficients as a function of the chemical shifts of the various species present in a mixture. This new work will extend considerably the range of diffusion coefficients which can be measured, while also providing better sensitivity and resolution. Supercritical carbon dioxide is a viable replacement for aqueous and organic solvent systems, especially the ozone-depleting chlorofluorocarbons. The research effort in fluoropolymers in supercritical fluids should prove critical to furthering the basic understanding of the chemistry and dynamics of these solution systems.
