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

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.