Diffusivities in Binary Mixtures of <i>n</i>-Decane, <i>n</i>-Hexadecane, <i>n</i>-Octacosane, 2-Methylpentane, 2,2-Dimethylbutane, Cyclohexane, Benzene, Ethanol, 1-Decanol, Ethyl Butanoate, or <i>n</i>-Hexanoic Acid with Dissolved He or Kr Close to Infinite Dilution

Abstract

Diffusive mass transport in binary mixtures of a liquid solvent and dissolved helium (He) or krypton (Kr) close to infinite dilution is investigated by determining the Fick diffusion coefficient D11 experimentally with dynamic light scattering (DLS). Equilibrium molecular dynamics (EMD) simulations are used to access the solute self-diffusion coefficient D1, which is equal to D11 at the limit of infinite dilution. To address how the molecular characteristics of the solvent influence molecular diffusion, a wide range of different solvents is considered, including n-decane, n-hexadecane, n-octacosane, ethanol, 1-decanol, cyclohexane, benzene, 2-methylpentane, 2,2-dimethylbutane, ethyl butanoate, and n-hexanoic acid. Mixtures are investigated between (303 and 448) K and up to 6.5 MPa. The average expanded experimental uncertainty (k = 2) of D11 from DLS experiments is 8.6%, and the average expanded statistical uncertainty (k = 2) of D1 from EMD simulations is 5.8%. Solvent force fields (FF) used in EMD simulations to describe interactions within and between molecules are primarily based on the all-atom optimized potentials for liquid simulation (OPLS) FF, and a temperature-dependent modification developed within our research group is applied. The average absolute relative deviation of the simulated D1 with respect to the experimental D11 is 14%. Results from DLS and EMD show that diffusive mass transport in mixtures containing dissolved He for a given solvent is (20–50)% greater than in those with Kr. In comparison to mixtures based on linear alkanes, those based on branched alkanes have larger D11, while mixtures based on oxygenated and cyclic components have smaller D11.

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