Intrinsic Structure of the Interface of Partially Miscible Fluids: An Application to Ionic Liquids

Abstract

This version is available at https://strathprints.strath.ac.uk/54829/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output. We investigate by means of Molecular Dynamics simulations how the intrinsic surface structure of liquid/liquid interfaces involving ionic liquids depends on the opposite phase of varying polarity. We study 1-n-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF 6 ) and 1-n-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imid (BMIM NTf 2 ). The opposite phase is either cyclohexane or water, but as a reference, IL -vacuum interfaces are also studied. We combine a distance-based cluster search algorithm with the ITIM intrinsic analyzing method to separate liquid phases showing non-negligible mutual miscibility and to identify atoms residing at the instantaneous surface. In contrast to the well structured surface of IL -vacuum systems, at liquid/liquid interfaces of ILs density correlations, ionic associations and orientational preferences are all weakened, this effect being much more pronounced when the other species is water. In such systems we observe a drastic reduction in the presence of the cation at the surface and an increase of appearance of polar moieties (of both the cations and anions) leading to decreased apolar character of the interface. Furthermore, cations are mostly found to turn with their butyl chains toward the bulk while having their methyl groups sticking towards water. Anion-cation associations are reduced and partially replaced by water-anion and rarely also water-cation associations.

On competitive gas adsorption and absorption phenomena in thin films of ionic liquids

“…Several studies show that these values provide optimum results for different uid phases, including ionic liquids. 38,48,49 Interfacial atoms are dened as the rst atoms touched by a probe sphere. Interfacial molecules are dened as those having at least one interfacial atom.…”

Investigation of the Liquid–Vapor Interface of Water–Formamide Mixtures by Computer Simulation and Intrinsic Surface Analysis

“…Since the pioneering work of Chacón and Tarazona, several such methods have been proposed in the literature, ,− some of which are not even limited by the assumption that the interface is macroscopically flat. − In the past decade, intrinsic surface analyzing methods have been widely and successfully applied to study the properties of the surface of several neat molecular − ,− and ionic liquids, − their mixtures, as well as of the binary molecular liquid mixtures − and aqueous electrolyte solutions . In such studies, a number of interface-related problems have been addressed, such as adsorption, − alignment − ,− and dynamics − of the interfacial molecules, association of molecules at the liquid surface, , explanation of the surface tension anomaly of water, , investigation of the properties of the Newton black films, the immersion depth of various surfactants in the liquid phase, or the plausibility of the “hydrogen cyanide (HCN) World” hypothesis concerning the prebiotic synthesis of biomolecules, analysis of the contribution of the subsequent subsurface molecular layers to the surface tension, and calculation of the profiles of various physical quantities, such as energy, density, ,,− solvation free energy,…”

Single Particle Dynamics at the Liquid–Liquid Interface. Molecular Dynamics Simulation Study of the Water-CCl4System

“…either with respect to this intrinsic surface, or in a layer-by-layer manner . In the past one and half decades, intrinsic analysis was successfully applied to the detailed characterization of the surface properties of various neat molecular liquids − ,− ,,,,, and their binary mixtures, ,− amorphous ice, , aqueous electrolyte solutions, Lennard-Jones systems, ,,,,,− ionic liquids − and their mixtures with molecular liquids, as well as of lipid membranes . Further, these methods helped clarifying a number of various problems related to soft interfaces, such as the explanation of the surface tension anomaly of water, , detecting the nonzero ideal gas contribution to the surface tension of liquids consisting of rigid particles, addressing the plausibility of the “HCN World” hypothesis that describes the possible prebiotic formation of the building blocks of large biomolecules, the immersion depth of various surfactants to water, the validity of the hypothesis that relates the spinodal pressure to the minimum of the interfacial lateral pressure profile, the behavior of Newton black films, as well as the surface adsorption ,− and surface orientation, including its dependence of the local surface curvature − ,− of various molecules.…”