Probing the structure of gas expanded liquids using relative permittivity, density and polarity measurements

Gas expanded liquids (GXLs) have been shown to be useful solvents with interesting properties between those of liquids and supercritical fluids. In this work the physical properties of 15 fluids are quantified at 50 bar CO₂ pressure and 25 °C and the data were used to gain an insight into the bulk and local structure upon pressurisation. It is shown that high CO₂ solubilities can be obtained in all solvents except the higher alcohols. Density measurements show that upon pressurisation the free volume of most solvents increases by up to 10%. The Kamlet and Taft and E_T parameters for the expanded solvents show that preferential solvation of the indicator solute occurs but that the ratio of solvent in the cybotactic and bulk regions remain roughly constant at a given pressure.