Solvatochromic characterization of near- and supercritical ethane, propane, and dimethyl ether using 9-(α-perfluoroheptyl-β,β-dicyano-vinyl)julolidine

Abstract

The solvatochromic dye 9(α-perfluoroheptyl-β,β-dicyanovinyl)julolidine is used to characterize the solvent strength of ethane, propane, and dimethyl ether over a pressure range of 35–300 bar at temperatures ranging from 25 to 155 °C. The results are consistent with the concept of clustering of the solvent molecules around the solute near the critical density. The direct relationship between the solvent's local density about the solute and it's isothermal compressibility, is shown to be valid not only at pressures above the critical pressure, but also at pressures below this value. Dimethyl ether is shown to be a highly adjustable solvent worth future consideration in supercritical fluid applications.