Molecular dynamics simulation on external wetted ionic liquid electrospray considering the asymmetric wetting behavior of cations and anions

The micro processes of the external wetted electrospray were investigated using molecular dynamics simulations. It was found that the asymmetric wetting behavior of the ions plays an important role in affecting the ion transportation and ion emission of the electrospray when varying the operation parameters. Increasing the wettability of the emitter, the wetting force difference between the cations and the anions increases proportionally, whereas the emission current reached the highest current 77 nA at a moderate wettability with the L-J well-depth ε_emitter = 0.6186 kcal/mol. Switching the electric field polarity to negative, hindered the ion transportation contributed by the wetting force difference and reduced the current by 39 %. Higher temperature (323 K) weakens the wetting force and the wetting force difference, thus increasing the emission current (83 nA) and emission of ion clusters with low charge to mass ratio. In addition, the higher electric field strength would lead to higher emission current, but an excessive electric field of 1 V/nm would lead to high plume divergence angle and unsteady ion emission. The present study provides useful information in controlling the emission characteristics of the external wetted electrospray and could promote its application in various fields.