(189x) Aggregation Behavior of 1-n-Dodecyl-3-Methylimidazolium Octylsulfate Biamphiphilic Ionic Liquid in Aqueous Solution

The structure and organization in an aqueous solution of ionic liquids for which either the cation or anion is responsible for inducing nonpolar domains are well understood. However, information regarding the aggregation behavior of such ionic liquids in aqueous solution is primitive at this point. The present contribution is aimed at addressing this question and focuses on a molecular dynamics study to probe aggregation features of aqueous 1-n-dodecyl-3-methylimidazolium [C₁₂mim] octylsulfate [C₈SO₄] solution and its vapor-liquid interface at room temperature. Previously, we have demonstrated that the presence of layer-like (polar–nonpolar–polar) morphology in bulk liquid phase of [C₁₂mim][C₈SO₄]. Our results indicate the formation of a single aggregate containing cations and anions of ionic liquids with evidence of lamellar morphology. The penetration of water in the nonpolar domain constituted by the alkyl tails is minimal, while the polar head groups are exposed to the bulk water. The introduction of vacuum interface induces spontaneous dissociation of the aggregate eventually leading to interfacial adsorption of cations and anions. Similar to surfactant molecules, the cationic and anionic polar heads orient towards the bulk water, while the nonpolar tails protrude out into vacuum. The structural characterization will be discussed in terms of number density profiles, orientation of the ions and aggregate number.