Fick Diffusion Coefficients and Thermal Diffusivities in Binary Liquid Mixtures Containing Alkanes and/or Cyclic Hydrocarbons by Using the Shadowgraph Method

The present work reports Fick diffusion coefficients D₁₁ and thermal diffusivities a of binary liquid mixtures containing n-heptane, 2,3-dimethylpentane, methylcyclohexane, toluene, n-decane, butylcyclohexane, butylbenzene, naphthalene, cis- or trans-decahydronaphthalene, 1,2,3,4-tetrahydronaphthalene, diphenylmethane, dicyclohexylmethane, ortho-benzyltoluene, or ortho-perhydrobenzyltoluene at equimolar composition determined by the shadowgraph method. Experiments were performed in the compressed liquid phase at temperatures T from (298 to 473) K and pressures p ≈ (0.1 to 1.4) MPa as well as at p from (0.1 to 30) MPa and T = 298 K or, studying a mixture of naphthalene and toluene, T = 373 K. D₁₁ and a were determined with average expanded experimental uncertainties (k = 2) of (13 and 8.0)% and their relationships to the molecular characteristics of the mixture components were analyzed. For D₁₁, dependencies on the molar mass, viscosity, and molecular structures such as branching, alkane (side) chain length, stereoisomerism, and aromatic or aliphatic rings of the mixture components were identified. Regarding a, only influences related to stereoisomerism as well as diphenylmethane, ortho-benzyltoluene, and their hydrogenated species were found. Additionally, the T-dependent D₁₁ and a data were compared to corresponding data from the literature.