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

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, H-1 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 H-1 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 [C(8)mim][Cl] showed that the microstructures consist of cubically packed molecules probably through pi-pi and hydrogen bond interactions.