# Collective orientational relaxation in a dense liquid of ellipsoidal molecules

Chandra, Amalendu and Bagchi, Biman (1990) Collective orientational relaxation in a dense liquid of ellipsoidal molecules. In: Physica A: Statistical and Theoretical Physics, 169 (2). pp. 246-262.

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Official URL: http://dx.doi.org/10.1016/0378-4371(90)90168-R

## Abstract

A molecular theory of collective orientational relaxation in a dense liquid of non-polar ellipsoidal molecules is presented. The theory is based on an extended hydrodynamic equation which is valid both at long and at small, molecular, length scales. The theory takes into account the intermolecular interactions among the liquid molecules through a force term derived from the density functional theory. We calculate the correlation functions $C_l_m(k, t) = \langle Y_l_m(-k) Y_l_m(k, t)\rangle$, where $Y_l_m(k, t)$ are the Fourier transformed spherical harmonics and l is the rank of the spherical harmonics. Analytic expressions for these correlation functions arc obtained for a pure liquid of ellipsoidal molecules. We find that because of the intermolecular orientational correlations among the ellipsoidal molecules, the relaxation of $C_2_m(k, t)$ is considerably different from its non-interacting limit. The collective orientational relaxation slows down because of the orientational correlations. This slowing down of the collective orientational relaxation increases with increase in the anisotropy of the molecular shape and also with increase in the density of the liquid. The translational modes of the liquid molecules can greatly accelerate the orientational relaxation at intermediate wavevectors.

Item Type: Journal Article Copyright of this article belongs to Elsevier Science. Division of Chemical Sciences > Solid State & Structural Chemistry Unit 02 Jul 2007 18 Jan 2012 06:46 http://eprints.iisc.ernet.in/id/eprint/11339