Structure and Dynamics of an Ionic Liquid Mixture Film Confined by Mica

Abstract

In a recent article (J. Phys. Chem. C 2019, 123, 4914−4925) we studied using molecular dynamics simulations the structure of an ionic liquid (IL) mixture comprised of 1-methyl-3octylimidazolium octylsulfate and 1-ethyl-3-methylimidazolium ethylsulfate confined by vacuum interfaces. At these interfaces, the mixture formed an apolar blocking layer concealing the smaller and more polar ions to the interior of the liquid phase. In the current work, and for the same IL mixture, we study the case of confinement between (001) mica surfaces, where the solid provides a flat and polar ionic interface. Our focus is twofold; first, we want to understand the structural and dynamical behaviors of the IL mixture at the boundary where the confining interface is highly polar, and second we want to establish how far away from the interface liquid behavior is recovered. This last point is particularly important in light of puzzling recent experimental results regarding the behavior of ILs and solutes dissolved in them under confinement, where large distances appear to be necessary to recover true bulk behavior. We find that the IL mixture is highly structured at the adlayer, but within 5 nm bulk-like structural features are recovered. Dynamical properties at the center of our thin film also appear converged to bulk behavior, but further studies are required to fully address the issue of dynamics within confined IL films.

Structure of Molten Alkali Chlorides at Charged Interfaces and the Prediction and Interpretation of Their X-ray Reflectivity

“…All atoms in the crystal were taken as neutral except when surfaces were charged at the location of the terminal CH 2 groups. The protocol we used for the equilibration of our systems, described in section , is similar to the one we used for mica at the interface of an IL in ref ; detailed information about final system sizes are provided in Table S.1. Even when considering the several approximations made to model these systems, and to the best of our knowledge, this is still one of the most realistic studies to date for ionic melts at neutral and charged interfaces since all atomic and ionic positions are treated explicitly and considered for our reflectivity calculations and electrical potential analysis.…”

From Water Solutions to Ionic Liquids with Solid State Nanopores as a Perspective to Study Transport and Translocation Phenomena

“…From the modeling perspective, the most effort was associated with determining the diffusion parallel to the pore IL. [137][138][139][140] Given that the symmetry of the system is preserved over this axis, self-diffusion coefficients may be obtained from mean square displacement (Einstein approach) [141] or the velocity autocorrelation function (Green-Kubo formalism). [142] It was shown that ions at the solid-liqud interface may strongly coordinate with particular moieties on the surface, which may impede their free diffusion (see Figure 6a).…”

Vacuum Interfacial Structure and X-ray Reflectivity of Imidazolium-Based Ionic Liquids with Perfluorinated Anions from a Theory and Simulations Perspective

“…The interfacial structure of C[2]-mim + /NTf 2 – at a sapphire surface was also investigated by using X-ray reflectivity in conjunction with MD simulations . Our group has also investigated ILs under confinement ,− using MD simulations, and in ref we developed the peaks and antipeaks analysis for reflectivity; the ideas introduced in ref were later expanded and applied to the study of diamond-confined molten alkali chloride salts . The literature on the structure of ILs using other surface sensitive techniques is vast, and a full set of citations is beyond the scope of this work, but particularly important has been the pioneering work by Baldelli et al using sum frequency generation − as well as Perkin et al , and Atkin et al using force microscopy. − …”