Solution thermodynamics near the liquid–liquid critical point. II. Excess second-order derivatives

Abstract

We present a comprehensive study of the behaviour of excess second-order derivatives of binary mixtures near the liquid–liquid critical point. Specifically, excess (isobaric and isochoric) molar heat capacities ( c p , x E and c V , x E ), excess (isothermal and isentropic) compressibilities ( κ T , x E and κ S , x E ), and excess isobaric thermal expansivities ( α p , x E ) have been determined over the whole composition ( x) range at atmospheric pressure and in the homogeneous region within (293.15–323.15) K. Results are consistent with the predictions of the current theory of critical phenomena. Remarkably, anomalous α p , x E ( x ) and κ T , x E ( x ) curves in the critical region are observed. Such anomalies, which are reported here for the first time, are of significant size for α p , x E and very mild in the case of κ T , x E ( x ) , thereby indicating that volumetric effects at near-liquid–liquid criticality are, as expected, very small.