The isothermal compressibility and surface tension product of room temperature ionic liquids

The isothermal compressibilities, κT, and surface tensions, σ, of room temperature ionic liquids (RTILs) were obtained from the literature. The products, κTσ, were compared, in analogy with high-melting ionic liquids (molten salts) and liquid metals, with expectations from the scaled particle theory, the correlation lengths, and the dependence on the cohesive energy density, but poor agreement was found. This behavior is ascribed to the 'loose' packing of the ions in the RTILs, due to the large, generally non-spherical ions making up these ionic liquids.