Effect of Lithium Ions on Rheology and Interfacial Forces in Ethylammonium Nitrate and Ethanolammonium Nitrate

The effect of added Li⁺ to two ionic liquids (ILs), ethylammonium nitrate (EAN) and ethanolammonium nitrate (EtAN), has been investigated using rheology and colloidal probe atomic force microscopy (AFM). Rheology data revealed a complex viscosity dependence that can be ascribed to the different bulk nanostructures. AFM force curves revealed steps for the neat ILs, analogous to those in previous studies. The addition of Li⁺ broadened the steps, which is likely an effect of ion clusters formed. Friction measurements corroborate this data and also showed that the structure of EtAN is much more prone to change as Li⁺ is added. These results demonstrate the complex behavior of ILs on interfaces and the effect of perturbing such interactions.