Phase equilibria and thermal properties of organic and fluoroorganic systems near the critical points of the liquid-vapor and liquid-liquid coexistence curves

Abstract

We performed experimental investigation of the temperature dependences of concentrations of the coexisting phases along liquid-liquid equilibrium lines of n-hexane-perfluorohexane (C₆H₁₄-C₆F₁₄) and n-heptane-perfluorohexane (C₇H₁₆-C₆F₁₄) binary systems with a miscibility gap. Furthermore, we investigated the temperature dependences of liquid and gas densities along saturation lines for pure perfluorobenzene (C₆F₆), pentafluorobenzene (C₆F₅H), perfluorohexane (C₆F₁₄), perfluorooctane (C₈F₁₈), and refrigerant R-236ea (CF₃-CHF-CHF₂). The measurements were performed in the temperature interval from 293 K up to the gas-liquid critical point or to the critical mixing point. The gamma-ray attenuation technique was used. The critical parameters (temperature, density, concentration) and critical indexes of the coexisting curves were determined with a high precision. An analysis of the obtained results confirms the existence of the contradiction mentioned in the literature between the experiments and scaling theory, which suggests universality of the critical exponents.