Abstract
AbstractFive new Gemini imidazolium surfactants were synthesized from imidazole and 1‐bromoalkane (C8, C10, C12, C14, C16) 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‐1H‐imidazol‐3‐ium) chloride. The structures of the five new surfactants and intermediates were characterized by 1H‐NMR, 13C‐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 (γCMC), adsorption efficiency (pC20), and effectiveness of surface tension reduction (πCMC). In addition, with application of the Gibbs adsorption isotherm, maximum surface excess concentration (Γmax) and minimum surface area/molecule (Amin) at the air–water interface were obtained. The parameters β (degree of counterion binding to micelles), ΔGadsθ (Gibbs free energy of adsorption), and ΔGmicθ (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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