Evidence of Extended Solidlike Layering in [Bmim][NTf2] Ionic Liquid Thin Films at Room-Temperature
Résumé
We report the direct observation of solidlike ordering at room temperature of thin films of [Bmim][NTf2]
ionic liquid on mica, amorphous silica, and oxidized Si(110). A statistical quantitative analysis of atomic
force microscopy topographies shows that on these surfaces [Bmim][NTf2] forms layered structures,
characterized by a perpendicular structural periodicity of ∼0.6 nm. Remarkably, even the highest structures,
up to 50 nm high, behave solidlike against the AFM probe. Conversely, on highly oriented pyrolitic graphite
the ionic liquid forms nanometer-sized, liquidlike domains. The results of this study are directly relevant for
those applications where ILs are employed in form of thin films supported on solid surfaces, such as in
microelectromechanical or microelectronic devices. More generally, they suggest that at the liquid/solid interface
the structural properties of ILs can be far more complex than those depicted so far, and prompt new fundamental
investigations of the forces that drive supported ILs through a liquidlike-to-solidlike transition.