Orientational order as the origin of the long-range hydrophobic effect

Banerjee, Saikat and Singh, Rakesh S and Bagchi, Biman (2015) Orientational order as the origin of the long-range hydrophobic effect. In: JOURNAL OF CHEMICAL PHYSICS, 142 (13).

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Abstract

The long range attractive force between two hydrophobic surfaces immersed in water is observed to decrease exponentially with their separation-this distance-dependence of effective force is known as the hydrophobic force law (HFL). We explore the microscopic origin of HFL by studying distance-dependent attraction between two parallel rods immersed in 2D Mercedes Benz model of water. This model is found to exhibit a well-defined HFL. Although the phenomenon is conventionally explained by density-dependent theories, we identify orientation, rather than density, as the relevant order parameter. The range of density variation is noticeably shorter than that of orientational heterogeneity. The latter is comparable to the observed distances of hydrophobic force. At large separation, attraction between the rods arises primarily from a destructive interference among the inwardly propagating oppositely oriented heterogeneity generated in water by the two rods. As the rods are brought closer, the interference increases leading to a decrease in heterogeneity and concomitant decrease in free energy of the system, giving rise to the effective attraction. We notice formation of hexagonal ice-like structures at the onset of attractive region which suggests that metastable free energy minimum may play a role in the origin of HFL. (C) 2015 AIP Publishing LLC.

Item Type:	Journal Article
Publication:	JOURNAL OF CHEMICAL PHYSICS
Publisher:	AMER INST PHYSICS
Additional Information:	Copy right for this article belongs to the AMER INST PHYSICS, 1305 WALT WHITMAN RD, STE 300, MELVILLE, NY 11747-4501 USA
Keywords:	LENNARD-JONES OBSTACLES; STATISTICAL-MECHANICS; WATER-STRUCTURE; MODEL; SURFACES; FORCES; ATTRACTION; MICA; TRANSITION; SOLVATION
Department/Centre:	Division of Chemical Sciences > Solid State & Structural Chemistry Unit
Date Deposited:	13 May 2015 06:59
Last Modified:	13 May 2015 06:59
URI:	http://eprints.iisc.ac.in/id/eprint/51514

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