Unique spatial heterogeneity in ionic liquids.

A multiscale coarse-graining model for ionic liquids has been extended to investigate the unique aggregation of cations in ionic liquids through computer simulation. It has been found that, with sufficiently long side chains, the tail groups of cations aggregate to form spatially heterogeneous domains, while headgroups of the cations and the anions distribute as uniformly as possible. This is understood as the result of competition between the charged electrostatic interactions between headgroups and anions and the collective short-range interactions between the neutral tail groups. This aggregation can help to explain a number of experimentally observed physical phenomena in ionic liquids.