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Boundary layer friction of solvate ionic liquids as a function of potential
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science. SP Technical Research Institute of Sweden, Sweden.
2017 (English)In: Faraday discussions (Online), ISSN 1359-6640, E-ISSN 1364-5498, Vol. 199, p. 311-322Article in journal (Refereed) Published
Abstract [en]

Atomic force microscopy (AFM) has been used to investigate the potential dependent boundary layer friction at solvate ionic liquid (SIL)-highly ordered pyrolytic graphite (HOPG) and SIL-Au(111) interfaces. Friction trace and retrace loops of lithium tetraglyme bis(trifluoromethylsulfonyl) amide (Li(G4) TFSI) at HOPG present clearer stick-slip events at negative potentials than at positive potentials, indicating that a Li+ cation layer adsorbed to the HOPG lattice at negative potentials which enhances stick-slip events. The boundary layer friction data for Li(G4) TFSI shows that at HOPG, friction forces at all potentials are low. The TFSI- anion rich boundary layer at positive potentials is more lubricating than the Li+ cation rich boundary layer at negative potentials. These results suggest that boundary layers at all potentials are smooth and energy is predominantly dissipated via stick-slip events. In contrast, friction at Au(111) for Li(G4) TFSI is significantly higher at positive potentials than at negative potentials, which is comparable to that at HOPG at the same potential. The similarity of boundary layer friction at negatively charged HOPG and Au(111) surfaces indicates that the boundary layer compositions are similar and rich in Li+ cations for both surfaces at negative potentials. However, at Au(111), the TFSI- rich boundary layer is less lubricating than the Li+ rich boundary layer, which implies that anion reorientations rather than stick-slip events are the predominant energy dissipation pathways. This is confirmed by the boundary friction of Li(G4) NO3 at Au(111), which shows similar friction to Li(G4) TFSI at negative potentials due to the same cation rich boundary layer composition, but even higher friction at positive potentials, due to higher energy dissipation in the NO3- rich boundary layer.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017. Vol. 199, p. 311-322
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-211347DOI: 10.1039/c6fd00236fISI: 000405429100016Scopus ID: 2-s2.0-85024131651OAI: oai:DiVA.org:kth-211347DiVA, id: diva2:1129087
Funder
Swedish Research Council, VR 621-2011-4361Knut and Alice Wallenberg Foundation, KAW2012.0078
Note

QC 20170801

Available from: 2017-08-01 Created: 2017-08-01 Last updated: 2017-08-01Bibliographically approved

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