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Unique diffusion behavior observed in supercritical ethanol

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Title: Unique diffusion behavior observed in supercritical ethanol
Authors: Ghosh, Swapan K. Browse this author
Tsujii, Kaoru Browse this author
Keywords: colloids
organic compounds
silicon compounds
Issue Date: 14-Apr-2010
Publisher: American Institute of Physics
Journal Title: Journal of Chemical Physics
Volume: 132
Issue: 14
Start Page: 144503
Publisher DOI: 10.1063/1.3373404
Abstract: We have systematically investigated the diffusion behavior of silica nanoparticles within supercritical ethanol, in terms of solvent properties by varying temperature (T) and pressure (P), to elucidate how the inhomogeneous solvent structures and density fluctuations in the solvent affect the diffusion behavior of solute particles. Results show that at a constant pressure, the diffusion coefficient (D) of the particles increases with increasing temperature, reaches the maximum (D^[max]) within the gaslike supercritical fluid (slightly below the ridge), and finally decreases abruptly at very low fluid density when temperature is increased further. Results reveal that D is appreciably larger than the theoretical prediction (Einstein-Stokes relationship) in the vicinity of the critical density (ρc) of the solvent. We interestingly observed that D becomes maximum (D^[max]) at a particular thermodynamic condition (Ti,Pi), which is expressed by the empirical formula T_[ri]=P^[0.16]_[ri] (for Tri>1, Pri>1). Here, Tri=Ti/Tc and P_[ri]=Pi/Pc; Tc and Pc are the temperature and the pressure at critical point, respectively. Results further reveal that D^[max] increases significantly with decreasing solvent density within the gaslike supercritical fluid where the changes in viscosities are negligible. These findings are unique, novel, and intriguing. We suggest that the enhancement of the diffusion coefficient in the vicinity of the critical density and the abrupt decrease in the diffusion coefficient in very low density gaslike fluid are associated with the change in the solvent-solvent and solute-solvent direct correlation function (related to the effective interaction potential) upon density change when the fluid crosses the ridge of density fluctuations and within the gaslike fluid.
Rights: Copyright 2010 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in J. Chem. Phys. 132, 144503 (2010) and may be found at
Type: article
Appears in Collections:電子科学研究所 (Research Institute for Electronic Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 辻井 薫

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