title: Force microscopy of layering and friction in an ionic liquid.
abstract: The mechanical properties of the ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([Py1,4][FAP]) in confinement between a SiOx and a Au(1 1 1) surface are investigated by means of atomic force microscopy (AFM) under electrochemical control. Up to 12 layers of ion pairs can be detected through force measurements while approaching the tip of the AFM to the surface. The particular shape of the force versus distance curve is explained by a model for the interaction between tip, gold surface and ionic liquid, which assumes an exponentially decaying oscillatory force originating from bulk liquid density correlations. Jumps in the tip-sample distance upon approach correspond to jumps of the compliant force sensor between branches of the oscillatory force curve. Frictional force between the laterally moving tip and the surface is detected only after partial penetration of the last double layer between tip and surface.
authors.affiliation: INM-Leibniz Institute for New Materials, Nanotribology Group, Saarbrücken, Germany. Department of Physics, Saarland University, Saarbrücken, Germany.
authors.forename: Judith
authors.initials: J
authors.lastname: Hoth
authors.forename: Florian
authors.initials: F
authors.lastname: Hausen
authors.forename: Martin H
authors.initials: MH
authors.lastname: Müser
authors.forename: Roland
authors.initials: R
authors.lastname: Bennewitz
mesh_terms: D000327:Adsorption; D017276:Friction; D052578:Ionic Liquids / Q000737:chemistry*; D008422:Materials Testing; D008567:Membranes, Artificial; D018625:Microscopy, Atomic Force / Q000379:methods*; D013314:Stress, Mechanical; D013499:Surface Properties; D013718:Tensile Strength
chemical_list: D052578:Ionic Liquids; D008567:Membranes, Artificial