Synthesis And Properties Of Tetrasiloxane Gemini Imidazolium Surfactants

Silicone surfactant is a highly efficient surfactant and it develops in recent years accompanied with new silicone materials developing, its surface activity performs very nice in not only aqueous but also non-aqueous solution, and it is gained widely attention because of its excellent spreadability, favorable wettability, low physiological toxicity and low environmental pollution. Gemini imidazolium surfactant with long carton chain has a stronger ability to lower surface tension and also has lower critical micelle concentration compared with single carton imidazolium surfactant. However, until now the study on Gemini imidazolium surfactant has been limited to hydrophobic long carton group, and the study on Gemini imidazolium surfactant with siloxane chain has not been reported.A new siloxane gemini imidazolium surfactant 3,3’-di[γ-tri(trimethylsiloxy)silyl]propyl-chloride-1,1’-(1,4-butanediyl)-bisimidazole ([Si4-4-Si4im]Cl2) was synthesized with chloro-trimethylsilane, γ-chloropropyltrichlorosilane,1,4-dichlorobutane and imidazole etc.. The structure of the surfactant was characterized by MS spectra and 1H NMR spectra, and the results proved that they were consistent with target structure. The surface tension of the surfactants was measured by Wilhelmy measuring plate method at 25℃. It indicates that the γcmc of [Si4-4-Si4im]Cl2 in aqueous solution can be reduced to 18.6 mN/m which is obviously better than long carton line Gemini imidazolium surfactants, and the cmc of [Si4-4-Si4im]Cl2 is 0.54 mmol/L which deceases by almost one order of magnitude compared with that of [Si4mim]Cl in literature [49]. The article also points out that the;γcmc of [Si4-4-Si4im]Cl2 is less than carton line Gemini imidazolium surfactants because of [Si4-4-Si4im]Cl2’s structure of similar "double umbrella" and the cmc of [Si4-4-Si4im]Cl2 is less than [Si4mim]CI because of its Gemini structure. The thermodynamic parameters of micellization(△GmΘ,△HmΘ, △SmΘ) of the surfactants were researched by determination of the electrical conductivity in different concentrations. The results give that the micellization of [Si4-4-Si4im]Cl2 is spontaneous, exothermic and entropydriven process at 15-35℃ in aqueous solution, the micellization of [Si4-6-Si4im]Cl2 is spontaneous, endothermic and entropydriven process at 15-35℃ in aqueous solution.