Relation between orientational correlation time and the self-diffusion coefficient of tagged probes in viscous liquids: A density functional theory analysis

Bagchi, Biman (2001) Relation between orientational correlation time and the self-diffusion coefficient of tagged probes in viscous liquids: A density functional theory analysis. In: Journal of Chemical Physics, 115 (5). pp. 2207-2211.

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Abstract

The usual explanation for the observed inverse relation between the orientational correlation time (\tau R) and the self-diffusion (DS) of a tagged solute probe in a viscous liquid is in terms of the hydrodynamic relations which are known to have dubious conceptual validity for small molecules. Here, we present a microscopic derivation of the relation between \tau R and DS. This derivation is based on the general ideas of the mode coupling theory, but uses the time-dependent density functional theory to obtain the torque-torque and force-force time correlation functions on the solute probe. Our analysis shows that the orientational correlation time (\tau R) is inversely proportional to the translational diffusion coefficient (D0) of the solvent molecules. Thus, the viscosity dependence of orientational correlation time enters through the viscosity dependence of the translational diffusion (D0). The same theoretical analysis also shows that the translational diffusion coefficient of the solute probe (DS) is also proportional to the translational diffusion coefficient, D0, of the solvent molecules. This result is in agreement with the recent computer simulation results which show that the product of \tau R and DS is a weak function of the density (hence of the viscosity) of the liquid. The microscopic expressions provide explanation, in terms of the solute-solvent direct correlation functions, the reason for the sensitivity of orientational diffusion to solute-solvent interaction potential.

Item Type:	Journal Article
Publication:	Journal of Chemical Physics
Publisher:	American Institute of Physics
Additional Information:	Copyright for this article belongs to American Institute of Physics (AIP).
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	14 Dec 2004
Last Modified:	19 Sep 2010 04:17
URI:	http://eprints.iisc.ac.in/id/eprint/2443

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