title: Nanoscale perturbations of room temperature ionic liquid structure at charged and uncharged interfaces.
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(+)][Tf(2)N(-)]) exhibits a mixed cation/anion layering with a strong interfacial densification of the first RTIL layer. The first 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 3.5 nm into the bulk fluid. The associated charge density profile demonstrates a pronounced charge overscreening (i.e., excess first-layer counterions with respect to the adjacent surface charge), highlighting the critical role of charge-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.
authors.affiliation: Chemical Science and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States.
authors.forename: Hua
authors.initials: H
authors.lastname: Zhou
authors.forename: Michael
authors.initials: M
authors.lastname: Rouha
authors.forename: Guang
authors.initials: G
authors.lastname: Feng
authors.forename: Sang Soo
authors.initials: SS
authors.lastname: Lee
authors.forename: Hugh
authors.initials: H
authors.lastname: Docherty
authors.forename: Paul
authors.initials: P
authors.lastname: Fenter
authors.forename: Peter T
authors.initials: PT
authors.lastname: Cummings
authors.forename: Pasquale F
authors.initials: PF
authors.lastname: Fulvio
authors.forename: Sheng
authors.initials: S
authors.lastname: Dai
authors.forename: John
authors.initials: J
authors.lastname: McDonough
authors.forename: Volker
authors.initials: V
authors.lastname: Presser
authors.forename: Yury
authors.initials: Y
authors.lastname: Gogotsi
mesh_terms: D003198:Computer Simulation; D004574:Electromagnetic Fields; D052578:Ionic Liquids / Q000737:chemistry*; D008422:Materials Testing; D008956:Models, Chemical; D008968:Molecular Conformation; D056004:Molecular Dynamics Simulation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D044367:Phase Transition; D013499:Surface Properties; D013696:Temperature
chemical_list: D052578:Ionic Liquids