We also calculated the electrostatic potential at the film surfaces for both additive and Drude systems (Figure ). For all systems, regions of negative potential were mostly coincident with oxygen atoms, whereas regions of positive potentials were closer to the aromatic ring atoms. A comparison between the distribution of electrostatic potential values of all systems can be found in Figure . For the additive systems, the electrostatic potential maps were similar for the systems in vacuum and in water (Figure and 7B) which is expected due to the lack of explicit electronic polarizability. That is, the partial charges assigned to each atom are invariant and therefore are not sensitive to environmental changes.