Ionic liquids (ILs) are used in contact with solid surfaces in many of their applications i.e. lubrication, electrochemistry, and biomass solvation. It is well known that liquids form ordered structures near surfaces, creating an interfacial layer which often exhibit properties very different from the same species in the bulk phase. ILs are known to form interfacial films that extend up to tens of nanometers from a solid surface. Our work employs a dynamic wetting technique to create IL films on solid substrates. This approach provides dynamic control over the film’s thickness, and allows <i>in situ</i> probing of the film’s molecular organization with spectroscopic techniques including IRRAS, sum frequency generation, and ellipsometry. In these films, we observe significant changes in the vibrational absorption profiles of IL molecules, which occur over several minutes to hours. These changes are assigned to the massive reorientation of IL molecules up to thousands of nanometers away from the solid surface. Overall, our data suggests reversible molecular ordering that extends throughout the entire thickness of the film (up to 2 μm). Results for various IL classes, surface materials and viscosities are compared for better understanding of IL behavior.

Reversible, micron-scale ordering in ionic liquid films

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.