Comparing the charge distribution along the surface normal in the [C6mim]+ ionic liquid with different anions

Concentration depth profiles of the elements in [C(6)mim]X (X = [BF4](-) and [Cl](-)) have been determined using neutral impact collision ion scattering spectroscopy in order to investigate how the choice of the anion influences the surface structure of the [C(6)mim](+) ionic liquids. The results show that the more polarisable, fluorinated anion [BF4](-), has a stronger tendency to adsorb to the surface compared to [Cl](-). While the [BF4](-) intermingles with the cation aliphatic chains, the decreased surface propensity of the [Cl](-) allows for the preferential orientation of the cation aliphatic chains pointing towards the vapour phase. Crown Copyright (C) 2012 Published by Elsevier B.V. All rights reserved.