Formation of Interconnected Aggregates in Aqueous Dicationic Ionic Liquid Solutions

The structure and organization in an aqueous solution of a gemini surfactant, the dicationic ionic liquid 1,3-bis(3-decylimidazolium-1-yl) propane bromide, and its vapor-liquid interface have been studied using molecular dynamics simulations at room temperature. Starting from a uniform distribution of cations, the system is found to spontaneously evolve forming crosslinked cationic micellar aggregates. Alkyl tails are typically found buried inside the aggregates to minimize their unfavorable interactions with water, whereas the polar head groups are present at the micellar surfaces, exposed to water. Anions are found throughout the solution and are not strongly bound to the cations. Cationic micellar aggregates exhibit an interesting behavior: interconnection mediated by head groups, a phenomenon which is not observed in monocationic ionic liquid solutions. The structure of the vapor-liquid interface of the solution, the structure of the micellar aggregates, and the distribution of counterions are also discussed.