  Using non-equilibrium molecular dynamics simulations and a coarse grained
model of ionic liquids, we have investigated the impact that the shape and the
intramolecular charge distribution of the ions have on the electrotuneable
friction with ionic-liquid nanoscale films. We show that the electric-field
induces significant structural changes in the film, leading to dramatic
modifications of the friction force. Comparison of the present work with
previous studies using different models of ionic liquids indicate that the
phenomenology presented here applies to a wide range of ionic liquids. In
particular, the electric-field-induced shift of the slippage plane from the
solid-liquid interface to the interior of the film and the non-monotonic
variation of the friction force are common features of ionic lubricants under
strong confinement. We also demonstrate that the molecular structure of the
ions plays an important role in determining the electrostriction and
electroswelling of the confined film, hence showing the importance of
ion-specific effects in electrotuneable friction.
