Surface Ordering in Binary Mixtures of Protic Ionic Liquids

Surface structure of a salty solution

30 January 2018

Probing the surface of a mixture of ionic liquids suggests it is not perfectly combined.

Ionic liquids are odourless, conductive salts that are liquids below 100 degrees Celsius. While they are an appealing option for environmentally friendly solvents and lubricants, their interface with air is not well studied. A team including researchers from Flinders University mixed two acid-based ionic liquids — ethylammonium nitrate (EAN) and propulammonium nitrate (PAN) — that, individually, combine perfectly with other substances. They probed the electronic structure of the outermost layer of the mixture and measured the surface tension. This was done in a vacuum to minimize evaporation. Their observations reveal that EAN and PAN are not perfectly mixed at the surface, with some sections being dominated by PAN.

Acid-based ionic liquids are cheap and easy to make, and understanding their surface properties when mixed together could help in the design of ‘green’ solvents.

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References

1. The Journal of Physical Chemistry Letters 8, 4264–4267 (2017). doi: 10.1021/acs.jpclett.7b01654