Surface tension and interfacial tension of binary organic liquid mixtures

The pendant drop method, combined with efficient temperature control of the measuring cell, allows high precision measurements of both surface tension and interfacial tension. The surface tensions and liquid densities of mixtures of cyclohexane + heptane, cyclohexane + propanone, and toluene + propanone have been determined at a normal pressure of 1 bar over the temperature range from 287 K to 317 K. The surface tension data could be parametrized with a cubic polynomial. Gibbs excess surface concentrations are derived from our experimental data, and the influence of activity coefficients is discussed. The high precision pendant drop apparatus allows accurate measurements of the interfacial tension in systems with liquid-liquid phase separation. In binary mixtures of heptane + N,N-dimethylformamide, heptane + N-methyl-2-pyrrolidone, and decane + N,N-dimethylformamide, the interfacial tension was measured over a wide temperature range close to the critical solution point. The densities of the corresponding liquid phases were obtained by buoyancy measurements. The accuracy of the density measurements is Deltarho = +/-0.0001 g(.)cm(-3) for the vibrating tube densimeter; for the buoyancy measurements we find Deltarho = +/-0.0005 g(.)cm(-3). The reproducibility of the surface tension measurements is generally better than Deltasigma = +/-0.50% at the 95% confidence level. Standard deviations for all experimental values are given in the tables. The resulting data are parametrized using polynomial and Wegener expansion type equations.