Liquid- or Solid-Like Behavior of [omim][BF4] at a Solid Interface?

The objective of this work is to clarify the nature of the lamellar structure reported by several authors for ionic liquids at solid interfaces. The ionic liquid 1-methyl-3-octylimidazolium tetrafluoroborate, [omim][BF4], has been deposited on a solid aluminum substrate from ethanol solutions and the resulting interfacial structure was investigated using atomic force microscopy imaging. The results have been analyzed using supplementary structural data obtained by molecular dynamics simulations. The main conclusion is that the behavior of the IL films is strongly dependent on time and concentration of the IL in solution. After 100 h of equilibration, the structure of the film changes as the concentration of the film-forming solution increases, reaching a sponge-like structure. At the concentration of 0.5 mg/mL, there is a drastic increase in the film maximum peak height that remains constant as the concentration further increases.