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ID 116439
著者
Nakahara, Masaru Kyoto University
資料タイプ
学術雑誌論文
抄録
The self-diffusion coefficients of water (Dw) and cyclohexane (Dch) 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 (xw) are studied in the ranges 0.62–6.35 M (M = mol dm−3), 250–400 °C, and 0.109–0.994, respectively. A polynomial fitting function was developed for a scaled value of Ξ = ρDT−1/2 with ρ, T, and xw 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 Dw and Dch in the dependence on ρ, T, and xw are characterized by the activation energy Ea and the activation volume ΔV‡Ξ expressed by the scaled fitting function. The decrease in the ratio Dw/Dch and the increase in the Ea of water with increasing xw are related to the increase in the number of hydrogen bonds (HBs). The Dw value for a solitary water molecule at a low xw 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.
掲載誌名
The Journal of Chemical Physics
ISSN
00219606
10897690
cat書誌ID
AA00694991
出版者
AIP Publishing
150
17
開始ページ
174505
発行日
2019-05-07
備考
This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Chem. Phys. 150, 174505 (2019) and may be found at https://doi.org/10.1063/1.5047540.
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言語
eng
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出版社版
部局
理工学系