Evidence of Extended Solidlike Layering in [Bmim][NTf2] Ionic Liquid Thin Films at Room-Temperature

Abstract

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 approximately 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.

A model to predict maximum tolerable temperatures of metal-oxide-supported 1- n -butyl-3-methylimidazolium based ionic liquids

“…The IL-loading in metal-oxide-supported samples corresponds to an IL-layer thickness of less than 0.8 nm on SiO 2 and γ-Al 2 O 3 (with a surface area of 212 and 209 m 2 /g, respectively), less than 1.5 nm on MgO (with a surface area of 99 m 2 /g), and less than 2.8 nm on TiO 2 (with a surface area of 55 m 2 /g). These thickness values, calculated according to surface area of metal-oxides and density of ILs, indicate single to a few molecular layers of ILs on metal-oxides, confirming the presence of interactions between metal-oxides and ILs (Bovio et al, 2009). If the thickness exceeds tens of nanometers, with increasing IL loading or decreasing metal-oxide surface area, it is expected to have a little influence of metal-oxide on thermal stability of IL, as most of the IL will exist without interfacial interactions with the surface.…”

Current trends in the physics of nanoscale friction

“…1. Similar quantized changes in film thickness and friction forces are observed also in confined liquid films [21][22][23], and should therefore be considered as a fundamental feature of highly-ordered closely-packed molecular films [24].…”

Interfaces between Charged Surfaces and Ionic Liquids: Insights from Molecular Simulations

“…22,46 Conclusions MD simulations of ionic liquid-electrode interfaces show that a transition from a multilayer ion structure to an ordered monolayer structure can be observed at certain values of the surface charge density. Upon this transition, a distinct change in the surface charge excess in the first two interfacial layers can be seen as a function of the renormalized surface charge density (on the κ-scale).…”