Synthesis, surface activity and aggregation behavior of Gemini imidazolium surfactants 1,3-bis(3-alkylimidazolium-1-yl) propane bromide

A novel class of Gemini imidazolium surfactants 1,3-bis(3-alkylimidazolium-1-yl) propane bromide [C n -3-C n im]Br 2 ( n   =   8, 10, 12) were synthesized and characterized by FT-IR, 1 H NMR and elemental analysis. The surface activity and aggregation behavior of [C n -3-C n im]Br 2 ( n   =   8, 10, 12) were investigated by surface tension, conductivity and steady fluorescence methods. A series of surface active parameters, including cmc, Γ max , p C 20 , cmc/ C 20 , A min , γ cmc and Π cmc were obtained from surface tension measurement. It was indicated that Gemini imidazolium surfactants with the longer alkyl chain showed the higher surface activity. The thermodynamic parameters of micellization process, namely, standard Gibbs free energy (Δ G m ο ), enthalpy (Δ H m ο ) and entropy (Δ S m ο ) were derived from conductivity measurement at different temperatures. The micropolarity and the mean aggregation number ( N agg ) of micelles were evaluated from steady fluorescence spectra. The results revealed that the micropolarity and N agg of micelles decreased with the increase of hydrocarbon chain length.