Version 2 2023-11-17, 21:07Version 2 2023-11-17, 21:07
Version 1 2023-11-16, 11:03Version 1 2023-11-16, 11:03
journal contribution
posted on 2023-11-17, 21:07authored byLayla Bou Tannous, Mirella Simoes Santos, Zheng Gong, Paul-Henri Haumesser, Anass Benayad, Agilio A. H. Padua, Audrey Steinberger
Room
temperature ionic liquids (ILs) can create a strong accumulation
of charges at solid interfaces by forming a very thin and dense electrical
double layer (EDL). The structure of this EDL has important consequences
in numerous applications involving ILs, for example, in supercapacitors,
sensors, and lubricants, by impacting the interfacial capacitance,
the charge carrier density of semiconductors, as well as the frictional
properties of the interfaces. We have studied the interfacial structure
of a long chain imidazolium-based IL (1-octyl-3-methylimidazolium
dicyanamide) on several substrates: mica, silica, silicon, and molybdenum
disulfide (MoS2), using atomic force microscopy (AFM) experiments
and molecular dynamics (MD) simulations. We have observed 3 types
of interfacial structures for the same IL, depending on the chemistry
of the substrate and the water content, showing that the EDL structure
is not an intrinsic property of the IL. We evidenced that at a low
water content, neutral and apolar (thus hydrophobic) substrates promote
a thin layer structure, where the ions are oriented parallel to the
substrate and cations and anions are mixed in each layer. In contrast,
a strongly charged (thus hydrophilic) substrate yields an extended
structuration into several bilayers, while a heterogeneous layering
with loose bilayer regions was observed on an intermediate polar and
weakly charged substrate and on an apolar one at a high bulk water
content. In the latter case, water contamination favors the formation
of bilayer patches by promoting the segregation of the long chain
IL into polar and apolar domains.