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A combination of carefully controlled tribological experiments and X-ray photoelectron spectroscopic analyses sheds light on the lubrication mechanisms of ionic liquids.
Ionic liquids (ILs) are remarkable fluids that consist of organic molecules that are either charged negatively (anions) or positively (cations) so that electrostatic forces keep them together, much in the same way as inorganic salts, such as sodium or potassium chloride. Because the organic fragments in ILs that surround the charged centers are much larger than in inorganic salts, the interactions are much weaker, so they tend to form liquids rather than solids. For the same reason, van derWaals' forces also contribute significantly to their intermolecular interactions. Consequently, they have exceedingly low vapor pressures and are therefore ideal candidates as space lubricants. There are now many thousand different types of ionicliquids with different ion combinations that display a wide range of tunable properties and potential applications, notably as lubricants, and in particular for use in electric vehicles.
However, despite their potential utility as lubricants, and perhaps because of their chemical complexity, little is known about...