(754a) Spreading of Nanoscale Droplets of Ionic Liquids on the Mica Surface

Extensive studies have been conducted on the molecular arrangement of ionic liquids (ILs) next to a solid surface. In these previous studies, mica has been utilized as a model solid surface due to its atomic-level smoothness and availability. The solid-like layering has been reported for many ILs on the mica surface. What remains unknown is the mobility of ILs confined to the solid mica surface: Are these solid-like layers mobile? There have been much less study on this topic and the previous results are inconsistent. In this paper, we report our recent AFM study on the spreading of the nanodroplets of an IL, 1-butyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate (BMIM-FAP), on the mica surface. The results indicate that the solid-like layers of IL are not real solid though their mobility is significantly lower than in bulk IL. As a result, the morphology of the nano-confined ILs on the solid surface could change significantly with time. The governing key parameters and the underlying mechanisms are discussed.