Synthesis and Surface Properties of Novel Gemini Imidazolium Surfactants
Five new Gemini imidazolium surfactants were synthesized from imidazole and 1-bromoalkane (C 8 , C 10 , C 12 , C 14 , C 16 ) to get 1-alkylimidazole, which was further reacted with 1,3-dichloropropan-2-ol to form the surfactant molecule, 1,1′-(propane-1,3-diyl-2-ol) bis(3-alkyl-1 H -imidazol-3-ium) chloride. The structures of the five new surfactants and intermediates were characterized by 1 H-NMR, 13 C-NMR and IR spectra. Thermal properties of the five new surfactants were studied with thermogravimetric analysis and differential scanning calorimetry, the five new surfactants showed a transition from a crystalline phase to a thermotropic liquid–crystalline phase at around ca. 100 °C, which transformed to an isotropic liquid phase at around ca. 165 °C. The five new surfactants critical micelle concentrations (CMC) in the aqueous solutions were determined by surface tension and electrical conductivity methods. The surface tension measurements provided a series of parameters, including critical micelle concentration (CMC), surface tension at the CMC ( γ CMC ), adsorption efficiency ( pC 20 ), and effectiveness of surface tension reduction (π CMC ). In addition, with application of the Gibbs adsorption isotherm, maximum surface excess concentration (Γ max ) and minimum surface area/molecule (A min ) at the air–water interface were obtained. The parameters β (degree of counterion binding to micelles), ΔG θ ads (Gibbs free energy of adsorption), and ΔG θ mic (Gibbs free energy change of micellization) were also derived. The results indicated that the five new Gemini surfactants exhibited very low CMC and a good efficiency in lowering the surface tension of water. The foamability and foam stability of the five new surfactants were also examined at different CMC.
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