Double layer in ionic liquids: the nature of the camel shape of capacitance

Monte Carlo simulations of a model ionic liquid show that if ions have charged heads and neutral counterparts, the latter give rise to the camel shape of the voltage dependence of the double layer capacitance. Neutral 'tails' of ions play the role of latent voids that can be replaced by charged groups via rotations and translations of ions. This provides extra degrees of freedom for the field-induced charge rearrangements in the double layer which results in the peculiar double-hump capacitance profile.