Unusual Behavior of the Thermodynamic Response Functions of Ionic Liquids

Abstract

The behavior of the isobaric molar heat capacity Cp, the isobaric thermal expansivity αp, and the isothermal compressibility κT of room-temperature ionic liquids (RTILs) is studied in detail. Accurate Cp(T,p), αp(T,p), and κT(T,p) results for a number of RTILs, as obtained by using appropriate experimental techniques, are presented and discussed. It is observed that αp decreases with T and that, consistently, Cp 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.