Surface active and aggregation behavior of methylimidazolium-based ionic liquids of type [C n mim] [X], n = 4, 6, 8 and [X] = Cl−, Br−, and I− in water

Abstract

The surface active and aggregation behavior of ionic liquids of type [C n mim][X] (1-alkyl-3-methylimidazolium (mim) halides), where n = 4, 6, 8 and [X] = Cl−, Br− and I− was investigated by using three techniques: surface tension, 1H nuclear magnetic resonance (NMR) spectroscopy, small-angle neutron scattering (SANS). A series of parameters including critical aggregation concentrations (CAC), surface active parameters and thermodynamic parameters of aggregation were calculated. The 1H NMR chemical shifts and SANS measurements reveal no evidence of aggregates for the short-chain 1-butylmim halides in water and however small oblate ellipsoidal shaped aggregates are formed by ionic liquids with 1-hexyl and 1-octyl chains. Analysis of SANS data analysis at higher concentrations of [C8mim][Cl] showed that the microstructures consist of cubically packed molecules probably through π–π and hydrogen bond interactions.