Spatial modulation of the composition of a binary liquid near a repulsive wall

Shibu Saw, S. M. Kamil, and Chandan Dasgupta
Phys. Rev. E 91, 052406 – Published 28 May 2015

Abstract

When a binary liquid is confined by a strongly repulsive wall, the local density is depleted near the wall and an interface similar to that between the liquid and its vapor is formed. This analogy suggests that the composition of the binary liquid near this interface should exhibit spatial modulation similar to that near a liquid-vapor interface even if the interactions of the wall with the two components of the liquid are the same. The Guggenheim adsorption relation quantifies the concentrations of two components of a binary mixture near a liquid-vapor interface and qualitatively states that the majority (minority) component enriches the interface for negative (positive) mixing energy if the surface tensions of the two components are not very different. From molecular dynamics simulations of binary mixtures with different compositions and interactions we find that the Guggenheim relation is qualitatively satisfied at wall-induced interfaces for systems with negative mixing energy at all state points considered. For systems with positive mixing energy, this relation is found to be qualitatively valid at low densities, while it is violated at state points with high density where correlations in the liquid are strong. This observation is validated by a calculation of the density profiles of the two components of the mixture using density functional theory with the Ramakrishnan-Yussouff free-energy functional. Possible reasons for the violation of the Guggenheim relation are discussed.

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  • Received 4 June 2014
  • Revised 16 March 2015

DOI:https://doi.org/10.1103/PhysRevE.91.052406

©2015 American Physical Society

Authors & Affiliations

Shibu Saw1,*, S. M. Kamil1,2,†, and Chandan Dasgupta1,‡

  • 1Department of Physics, Centre for Condensed Matter Theory, Indian Institute of Science, Bangalore 560012, India
  • 2Department of Physics, School of Natural Sciences, Shiv Nadar University, Gautam Budh Nagar 201314, India

  • *shibu@physics.iisc.ernet.in
  • kamil.syed@snu.edu.in
  • cdgupta@physics.iisc.ernet.in

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Vol. 91, Iss. 5 — May 2015

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