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American Chemical Society, ACS Nano, 11(6), p. 9818-9827, 2012

DOI: 10.1021/nn303355b

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Nanoscale Perturbations of Room Temperature Ionic Liquid Structure at Charged and Uncharged Interfaces

This paper is available in a repository.
This paper is available in a repository.

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Abstract

The nanoscale interactions of room temperature ionic liquids (RTILs) at uncharged (graphene) and charged (muscovite mica) solid surfaces were evaluated with high resolution X-ray interface scattering and fully atomistic molecular dynamics simulations. At uncharged graphene surfaces, the imidazolium-based RTIL ([bmim+][Tf2N-]) exhibits a mixed cation/anion layering with a strong interfacial densification of the first RTIL layer. The 1st layer density observed via experiment is larger than that predicted by simulation and the apparent discrepancy can be understood with the inclusion of, dominantly, image charge and π-stacking interactions between the RTIL and the graphene sheet. In contrast, the RTIL structure adjacent to the charged mica surface exhibits an alternating cation-anion layering extending 2-3 nm into the bulk fluid. The associated charge density profile demonstrates a pronounced charge over-screening (i.e., excess first-layer counterions with respect to the adjacent surface charge), highlighting the critical role of charged-induced nanoscale correlations of the RTIL. These observations confirm key aspects of a predicted electric double layer structure from an analytical Landau-Ginzburg-type continuum theory incorporating ion correlation effects, and provide a new baseline for understanding the fundamental nanoscale response of RTILs at charged interfaces.