Thermodynamics Research Center / ThermoML | Journal of Chemical and Engineering Data

ABSTRACT

Thermophysical properties (densities, speeds of sound, bulk moduli, and viscosities) of binary mixtures of n-alkylcyclohexanes (propyl- to dodecylcyclohexane) with n-dodecane were examined as a function of composition and temperature (293.15 to 333.15) K. Viscosities were modeled using the McAllister three-body equation. Excess molar Gibbs energies of activation for viscous flow at 293.15 K were not statistically different from zero, which suggests ideal behavior. In contrast, nonzero excess molar volumes obtained both experimentally and using Molecular Dynamics simulations suggest nonideal behavior. Excess molar volumes were the most negative for n-dodecylcyclohexane mixtures and increased with decreasing alkyl side-chain length eventually becoming slightly positive for mixtures containing n-propylcyclohexane. MD simulations were able to predict density and isentropic bulk modulus values, but the accuracy of the calculated densities decreased slightly with increasing temperature. Voronoi tessellation was used to calculate histograms of molecular volumes in the mixtures. The most probable volume of n-dodecane increases and decreases when mixed with n-propylcyclohexane or ndodecylcyclohexane, respectively. These shifts in molar volume are responsible for the expansion and contraction upon mixing observed in the excess molar volume data. Volume contraction (negative excess molar volume) produces mixture speeds of sound that are faster than ideal (positive excess speed of sound) unless confounded by opposing compressibility differences. Excess speeds of sound were positive for n-dodecylcyclohexane mixtures, decreased as the alkyl side-chain length increased, and were negative for n-propylcyclohexane mixtures.