徳島大学 教育・研究者情報データベース(EDB)

1. 吉田 健([徳島大学.大学院社会産業理工学研究部.理工学域.応用化学系.物質機能化学分野]/[徳島大学.理工学部.理工学科.応用化学システムコース.物質機能化学講座])

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2. (英) Nakahara Masaru

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(英) Self-diffusion of water-cyclohexane mixtures in supercritical conditions as studied by NMR and molecular dynamics simulation

(英) The self-diffusion coefficients of water (D) and cyclohexane (D) in their binary mixtures were determined using the proton pulsed field gradient spin-echo method from medium to low densities in subcritical and supercritical conditions. The density (ϱ), temperature (T), and water mole fraction (x) are studied in the ranges 0.62-6.35 M (M = mol dm), 250-400 °C, and 0.109-0.994, respectively. A polynomial fitting function was developed for a scaled value of Ξ = ϱDT with ϱ, T, and x as variables in combination with a comprehensive molecular dynamics (MD) simulation. The NMR and MD results agree within 5% for water and 6% for cyclohexane, on average. The differences between D and D in the dependence on ϱ, T, and x are characterized by the activation energy E and the activation volume ΔV expressed by the scaled fitting function. The decrease in the ratio D/D and the increase in the E of water with increasing x are related to the increase in the number of hydrogen bonds (HBs). The D value for a solitary water molecule at a low x is controlled by the solvation shell, most of which is occupied by nonpolar cyclohexane molecules that provide less friction as a result of weaker interactions with water. A microscopic diffusion mechanism is discussed based on an analysis of the HB number as well as the first-peak height of the radial distribution functions that are taken as measures of the potential of the mean field controlling self-diffusion.

1. (英) Article.ELocationID: 10.1063/1.5047540

2. (英) Article.PublicationTypeList.PublicationType: Journal Article