​Ionic liquids have the potential for application in a range of industries, including green energy technologies such as fuel cells and providing lubrication by changing surface charges and reducing friction. However, the presence of water in an ionic liquid can have a big influence on its properties and, where halogens are present, react to produce toxic by-products. 

By studying a halogen-free ionic liquid and its interactions with a gold surface under both wet and dry conditions, researchers have been able to gain an insight into how the presence of water influences these interactions. The charged nature of the ionic liquid means that its interfacial properties can be controlled using an applied potential, and the group found that this control was strongly affected by the presence of water but that it was still possible to achieve. 

The researchers also studied the effect of changing the alkyl chain length of components of a non-halogenated ionic liquid. They found that, if the alkyl chain is sufficiently long, the interaction between the molecules becomes more dominant than that from the charged surface, with the longer chain liquids forming cation bilayers. 

These two studies confirm the feasibility of using nonhalogenated ionic liquids for lubrication, even in the presence of water. Further investigations into the wear behaviour of the system will inform its feasibility for wider use.

Related publication: “Effect of water on the electroresponsive structuring and friction in dilute and concentrated ionic liquid lubricant mixtures.” Phys. Chem. Chem. Phys., 22, 28191-28201 (2020); “Interfacial structuring of non-halogenated imidazolium ionic liquids at charged surfaces: effect of alkyl chain length.” Phys. Chem. Chem. Phys., 22, 8450-8460 (2020) 

DOI: 10.1039/D0CP05110A; DOI: 10.1039/D0CP00360C