Volumetric, ultrasonic, viscometric and refractive index behavior of binary mixtures of 2,2,4-trimethylpentane with aromatic hydrocarbons: An experimental and theoretical study

Measurements of densities, ρ, ultrasonic speeds, u, viscosities, η, and refractive indices, n have been carried out for binary mixtures of 2,2,4-trimethylpentane (TMP) with benzene, toluene, o-xylene, m-xylene, and p-xylene, including those of pure liquids, at 35 °C over the entire composition range. From these experimental data, the values of excess molar volumes, VE, deviations in isentropic compressibilities, Δks, and viscosities, Δη, excess Gibbs free energy of activation of viscous flow, G⁎E, deviations in refractive indices, Δn, and partial molar isentropic compressibility, K¯2°, of aromatic hydrocarbons in TMP at infinite dilution were calculated. The variations of these parameters with composition of the mixtures suggest an increasingly better packing of plate-like aromatic molecules into the spaces created by globular-shaped TMP molecules in the sequence: benzene < toluene < m-xylene ≈ p-xylene < o-xylene. Further, for xylenes, the magnitude of these derived parameters is found to depend on the position of -CH3 groups in the molecule. The excess molar volumes, VE, of the mixtures have also been predicted from Flory's statistical theory and the Prigogine-Flory-Patterson (PFP) theory. Using Flory theory and rigid hard sphere models, the values of isothermal compressibilities, kT, of the present binary mixtures were evaluated and compared with the experimental values. Moreover, theoretical evaluation of viscosity by using one-, two- and three-parameter equations suggests the superiority of the three-parameter equation over one- and two-parameter equations.