Layering and shear properties of an ionic liquid, 1-ethyl-3-methylimidazolium ethylsulfate, confined to nano-films between mica surfaces
- 8 December 2009
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Physical Chemistry Chemical Physics
- Vol. 12 (6), 1243-1247
- https://doi.org/10.1039/b920571c
Abstract
We report high-resolution measurements of the forces between two atomically smooth solid surfaces across a film of 1-ethyl-3-methylimidazolium ethylsulfate ionic liquid, for film thickness down to a single ion diameter. For films thinner than ∼2 nm oscillatory structural forces are observed as the surface separation decreases and pairs of ion layers are squeezed out of the film. Strikingly, measurements of the shear stress of the ionic liquid film reveal low friction coefficients which are 1–2 orders of magnitude smaller than for analogous films of non-polar molecular liquids, including standard hydrocarbon lubricants, up to ca. 1 MPa pressure. We attribute this to the geometric and charge characteristics of the ionic liquid: the irregular shapes of the ions lead to a low shear stress, while the strong coulombic interactions between the ions and the charged confining surfaces lead to a robust film which is maintained between the shearing surfaces when pressure is applied across the film.Keywords
This publication has 26 references indexed in Scilit:
- Ionic-liquid materials for the electrochemical challenges of the futureNature Materials, 2009
- Dipole Correlations in the Ionic Liquid 1-N-Ethyl-3-N-methylimidazolium Ethylsulfate and Its Binary Mixtures with DichloromethaneThe Journal of Physical Chemistry B, 2009
- Growth of Silicon Nanowires of Controlled Diameters by Electrodeposition in Ionic Liquid at Room TemperatureNano Letters, 2008
- Ionic Liquid Near a Charged Wall: Structure and Capacitance of Electrical Double LayerThe Journal of Physical Chemistry B, 2008
- High-performance dye-sensitized solar cells based on solvent-free electrolytes produced from eutectic meltsNature Materials, 2008
- Simulations of Ionic Liquids, Solutions, and SurfacesAccounts of Chemical Research, 2007
- Double-Layer in Ionic Liquids: Paradigm Change?The Journal of Physical Chemistry B, 2007
- Electrochemical interface between an ionic liquid and a model metallic electrodeThe Journal of Chemical Physics, 2007
- Transitions between smooth and complex stick-slip sliding of surfacesPhysical Review E, 2003
- Double-layer and solvation forces measured in a molten salt and its mixtures with waterThe Journal of Physical Chemistry, 1988