Nanoconfined ionic liquids: A computational study

In this work we study how the properties of ionic liquids change upon confinement between two walls at various nanometric distances. We also find a correlation between the dynamic properties and the structure of this system under these extremely nanoconfined circumstances. We report that for ethylammonium nitrate, the ionic structure inside the simulation boxes is a consequence of a subtle combination of ion packing, hydrogen bonding, electrostatic and van der Waals forces. We also study how the dynamical properties of this material change in these conditions, showing a decrease in the ionic mobility for very low slit sizes, recovering the bulk behavior as the distance between walls increases. Moreover, when short wall separations are considered, we show that the ionic mobility at short times is a minimum when the hydrogen bonding is also a minimum. Finally, we show that the effect of the interface in the long time ion dynamics only extends to a quite small region (ca. 1.35 nm) next to the walls. We show that the overall behavior of the nanoconfined liquid in the slit pore can be described by the superposition of a bulk and a confined simulation with a fitted wall separation. To our knowledge, there are no similar studies characterizing this kind of dense ionic systems in such a fine-grain way under these ultra-nanoconfined conditions.