Densities, Heat Capacities and Asymmetric Criticality of Coexistence Curves for Binary Mixtures {Dimethyl Adipate + n-Heptane or n-Octane}

Abstract

Densities of binary mixtures {x dimethyl adipate + (1 − x) n-heptane} and {x dimethyl adipate + (1 − x) n-octane} were measured at various temperatures. The excess molar volumes were calculated from the density data and fitted with the Redlich–Kister equation. The critical anomaly of density was detected for {x dimethyl adipate + (1 − x) n-octane} binary solutions with the critical compositions in a narrow temperature range of the near-critical one-phase region. However, the density anomaly and the excess properties were taken into account in a test of the complete scaling theory and found to be negligible. The isobaric heat capacities per unit volume of the {x dimethyl adipate + (1 − x) n-heptane} and {x dimethyl adipate + (1 − x) n-octane} binary solutions at the critical compositions were also determined over the temperature range both near and far away from the critical points. It was found that the heat capacity plays an important role in describing the asymmetry of the coexistence curves.