Application of Solvatochromic Probes to Supercritical and Mixed Fluid Solvents

摘要

Changes of the polarity/polarizability of supercritical CO sub 2 , N sub 2 O, Freon-13, NH sub 3 , and CO sub 2 /methanol mixtures, were measured by observing the shift of the uv absorption of 2-nitroanisole as a function of temperature and pressure. The polarities of the supercritical fluid solvents are compared to those of liquid solvents through use of the Kamlet-Taft pi * polarity scale. In the pure fluid solvents the polarity was found to be correlated primarily with density. The data for CO sub 2 indicate that a change in the cybotatic region occurs at a fluid density of approx.0.3 gm/cm exp 3 . Adding methanol as a modifer to supercritical CO sub 2 gradually increases the polarity of the solvent; in solutions with over 10% methanol the composition of the cybotatic region appears to differ from the bulk composition, being enriched in methanol. 25 refs., 7 figs., 2 tabs. (ERA citation 11:020555)