NMR Studies of Solid-Supercritical Fluid Mixtures and a New Technique for NMR Diffusion Measurements

83 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.Solid solubilities of naphthalene in supercritical carbon dioxide have been measured near the upper critical end point of the binary mixture by using a novel, in situ NMR technique. The pressure-temperature trace of the solid-liquid-gas phase line that terminates at the upper critical end point was also determined. The results are discussed in terms of the supercritical solubility theory of Gitterman and Procaccia. The analysis correlates the composition and phase data.The use of supercritical fluid solvents to obtain NMR line narrowing for solutes containing quadrupolar nuclei was investigated. It is shown that for certain solute-supercritical fluid systems linewidth improvements of two to six fold over organic solvents are possible.A new technique for diffusion measurement by NMR using a fixed field gradient is described. The method makes use of a Bessel function fit analysis to the spin-echo signal in order to determine both the applied gradient and the diffusion coefficient simultaneously. Results of tests of the method are presented, and the utility of the technique is demonstrated.An NMR study of the molecular motions of naphthalene in the naphthalene-supercritical carbon dioxide mixture was performed. Both the diffusion coefficient of naphthalene and the deuterium spin lattice relaxation time of d$\sb8$-naphthalene have been measured. Data have been obtained over two distinct phase regions of the mixture. The results are analyzed using hydrodynamic theory through the Stokes-Einstein and Debye equations. Empirical modifications of these equations are necessary to represent the data.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD