Asymmetric liquid-liquid criticality in the ideal volumetric mixing approximation

Abstract We address the question on the validity of the ideal volumetric mixing approximation, a customarily used approach to analyze liquid-liquid phase transitions. Thus, liquid-liquid coexistence curves for the binary mixture composed by nitromethane and 3-pentanol were obtained from direct single-phase mass density measurements as a function of temperature. A reasonable agreement with previously reported data obtained from refractive index measurements has been found, indicating that assuming ideal mixing is rather reasonable. Furthermore, the implications of the ideal volumetric mixing approximation on asymmetric liquid-liquid criticality are explored in the framework of complete scaling formulation, with emphasis on the coexistence curves in the mole fraction-temperature and volume fraction-temperature planes as well as on the behaviour of the isobaric heat capacity per particle and per unit volume and the associated Yang-Yang-type anomalies.