Force microscopy of layering and friction in an ionic liquid

Judith Hoth, Florian Hausen, Martin H Müser, Roland Bennewitz
2014 Journal of Physics: Condensed Matter  
The mechanical properties of the ionic liquid 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl) trifluorophosphate ([Py 1,4 ][FAP]) in confinement between a SiO x and a Au(111) surface are investigated by means of atomic force microscopy (AFM) under electrochemical control. Up to twelve 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 vs. distance curve is explained by a model for the
more » ... ion 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.
doi:10.1088/0953-8984/26/28/284110 pmid:24919549 fatcat:5mr3w3qbjfe6dbzq6mi4jqh5ga