Nanodomain organization in ionic liquids: Implications of polarization effects in the alkyl side-chain association

Abstract

The existence of domains at the nanometric scale has been observed in ionic liquids with long alkyl side chains. Experimental evidence and theoretical studies have suggested the existence of nanodomains with polar and non-polar characteristics. This evidence has been related to the capacity of ionic liquids to dissolve species within a broad range of chemical properties. Herein, we present a study of the structural features of the non-polar domain using classical molecular dynamics using a polarizable force field. The results suggest that the tail-to-tail association is stronger when a polarizable force field is used, owing to the better description of the dispersive forces between them. We propose using a polarizable force field in the simulations of ionic liquids based on classical molecular dynamics as the default method. To account for these differences, we compare the non-polarizable force field and its polarizable variant in describing the self-association of long-tailed imidazolium-based ionic liquids. Finally, a nanodomain analysis could rationalize the solute-solvent interactions brought about by ionic liquid since they strongly depend on the hydrogen-bond acidity and basicity, which are expected to operate in the polar domain.