Cation Exchange at the Interfaces of Ultrathin Films of Fluorous Ionic Liquids on Ag(111)

[Image: see text] In the context of applications with thin ionic liquid (IL) films on solid supports, we studied the ion distribution within mixed thin IL films by angle-resolved X-ray photoelectron spectroscopy. After the deposition of 1-methyl-3-octylimidazolium hexafluorophosphate, [C(8)C(1)Im][PF(6)], on top of a wetting layer (WL) of 3-methyl-1-(3,3,4,4,4-pentafluorobutyl)imidazolium hexafluorophosphate, [PFBMIm][PF(6)], on Ag(111) at room temperature (RT), we find a preferential enrichment of the [PFBMIm](+) cation at the IL/vacuum interface. In a similar deposition experiment at 82 K, this cation exchange at the IL/solid interface does not occur. Upon heating the film from 82 K to RT, we observe the replacement of [C(8)C(1)Im](+) by [PFBMIm](+) at the IL/vacuum interface between ∼160 and ∼220 K. No further changes in the surface composition were observed between 220 K and RT. Upon further heating the mixed IL film, we find the complete desorption of [PFBMIm][PF(6)] from the mixed film below 410 K, leaving a WL of pure [C(8)C(1)Im][PF(6)] on Ag(111), which desorbs until 455 K.