Surface structures of equimolar mixtures of imidazolium-based ionic liquids using high-resolution Rutherford backscattering spectroscopy

► Surface structures of mixtures of imidazolium-based ionic liquids were studied. ► Composition depth profiles were measured using high-resolution RBS. ► Both cations and anions have the same preferential orientations at the surface as in the pure ILs. ► In the mixture, the larger anion is located shallower than the smaller anion. ► The [TFSI] anion is slightly enriched at the surface relative to [PF6].