Unusual Behavior of the Thermodynamic Response Functions of Ionic Liquids

The behavior of the isobaric molar heat capacity C p, the isobaric thermal expansivity α p, and the isothermal compressibility κ T of room-temperature ionic liquids (RTILs) is studied in detail. Accurate C p ( T, p ), α p ( T, p ), and κ T ( T, p ) results for a number of RTILs, as obtained by using appropriate experimental techniques, are presented and discussed. It is observed that α p decreases with T and that, consistently, C p increases with p, thereby clarifying previous controversial results. The whole experimental picture is coincident with that of a fluid characterized by a high degree of cohesion. Such conclusion arises from the analysis of some loci of extrema of the above thermodynamic response functions as obtained from an equation of state based on thermodynamic perturbation theory.