Ionic Liquids at Nonane–Water Interfaces : Molecular Dynamics Studies

Abstract

The structures of ternary systems with water, nonane, and an ionic liquid, with the ionic liquid placed between water and nonane, have been studied using atomistic molecular dynamics simulations. Three different ionic liquids with 1-n-butyl-3-methylimidazolium cation and bromide, tetrafluoroborate, and trifluoromethanesulfonate anions have been studied. The ionic liquids disperse into the aqueous phase quickly and are solubilized in water within 15 ns to form two equivalent nonane–aqueous ionic liquid interfaces. The interfacial region is enriched with ionic liquids due to the amphiphilicity of the cations. The presence of ionic liquids at the interface reduces the interfacial tension between the nonane and water, thus facilitating the mixing of aqueous and nonane phases. The reduction in the interfacial tension is found to be inversely related to the solubility of the corresponding ionic liquid in water. The butyl chains of the cations and the trifluoromethanesulfonate anions present in the interfacial region are found to be preferentially oriented parallel to the interface normal.