Surface Properties of Ionic Liquids: A Mass Spectrometric View Based on Soft Cluster-Induced Desorption

Desorption/ionization induced by neutral clusters (DINeC) in combination with mass spectrometry (MS) was used for the investigation of the molecular composition of the surface of ionic liquids (IL). Based on the surface sensitivity of DINeC-MS, accumulation of either cations or anions was discriminated on the surface of bulk IL depending on the molecular structure of the IL components. In particular, cations with long alkyl chains aggregate on the surface, but this tendency is more reduced the larger the respective anion is; in the case of larger anions and smaller cations, it can be even reversed. For thin layers of IL, the ratio between cations and anions as detected in the mass spectra was found to be further influenced by the substrate surface.