Synthesis And Aggregation Behaviors Of Gemini Imidazolium Surfactants And Their Siloxane Derivatives

The dissymmetric Gemini surfactants consist of different hydrophilic head groups.different hydrophobic chains and various spacer groups,which makes them have richer adjustable factors in molecular structure than symmetric Gemini surfactants.Therefore.they display more novel and complex self-assembly behaviors.Additionally,organosilicone surfactants with siloxane hydrophobic groups have excellent performance,such as higher surface activity,super wetting ability,nontoxicity and non-corrosiveness,which will make them be new development direction and research spotlight.Gemini imidazolium surfactants combine the properties of the traditional cationic Gemini surfactants with single-chain imidazolium surfactants,which makes them have an extremely important application value in the food,cosmetics,industries,and so on.In this dissertation.using Gemini imidazolium surfactant as the research object.the dissymmetric Gemini imidazolium surfactants with alkyl hydrophobic chains and the symmetric Gemini imidazolium surfactants with siloxane hydrophobic chains were designed and studied.The major works were listed below:A series of symmetric and dissymmetric Gemini imidazolium surfactants,including[CmC2Cnim]Br2.[CmC4Cnim]Br2,[CmC6Cnim]Br2(n = 6.8,10,12,m + n = 24)and[C14C4Cnim]Br2(n = 12.14).have been synthesized.Their structures were characterized by 1H NMR.13C NMR?FTIR and MS(ESI)spectroscopy and the results indicated that these surfactants were all objective products.Besides,in the synthetic process of 1-(4-bromobutyl)-3-decylimidazolium bromide.the better reaction conditions were confirmed by the method of single factor experiments:the reaction temperature was 50? the time 10 h.n(N-decyl imidazole):n(1.4-dibromobutane)1:4 and the volume of solvent was 5?8 times of the total mass of reactants.The surface activity,micellization.micellar micropolarity,micellar aggregation number and aggregates size of[CmC2Cnim]Br2,[CmC4Cnim]Br2.[CmC6Cnim]Br2 and[C14C4Cnim]Br2 were investigated by means of surface tension,electrical conductivity.steady-state fluorescence and dynamic light scattering.The results showed that for the[CmCsCnim]Br2 series with the same s.the increase of dissymmetric degree can enhance the ability of forming micelles,the efficiency of reducing surface tension and enthalpy driving force.On the other hand,when the dissymmetric degree was same,the increase of spacer groups made the ability and efficiency of reducing surface tension decrease.For[C14C4Cnim]Br2 series,fixing one alkyl chain length and increasing another length led to the stronger micelles formation ability.the efficiency and ability of lowing surface tension and enthalpy driving force of self-organization behavior.The micellization for all Gemini imidazolium surfactants was spontaneous,exothermic and entropy-driven process.The fluorescence measurements showed that for[CmC4Cnim]Br2 or[C14C4Cnim]Br2 series,micellar micropolarity was almost same,and micellar aggregation number increased with increasing the dissymmetric degree or overall alkyl chains length.For[C14CsC10im]Br2 series,the increase of spacer groups made micellar micropolarity increase and micellar aggregation number decrease.Dynamic light scattering experiments indicated that Gemini imidazolium surfactants not only can form smaller micelles but also can form the aggregates with larger size.Gemini imidazolium surfactants with different siloxane chain and spacer groups([Si3CsSi3im]C12?[Si4CsSi4im]Cl2,s=4,6,8)were synthesized and the results ofiH NMR?13C NMR?FTIR and MS(ESI)spectroscopy indicated that these siloxane chain surfactants were all objective products.In the synthetic process of[Si3C4Si3im]I2.the better conditions of quaternarization reaction were as follows:the reaction temperature was 75?.the time 48 h.and n(3-iodopropyl methyl di(trimethylsiloxy)silane):n(1.4-bis(imidazol-l-yl)butane)was 2.5:1.The aggregation behaviors in aqueous solution of[Si3CsSi3im]Cl2 and[Si4CSSi4im]Cl2 were studied by the methods of surface tension,electrical conductivity.steady-state fluorescence and dynamic light scattering.Surface tension of water can be reduced to 20?26 mN/m with the addition of[Si3CsSi3im]Cl2 or[Si4CsSi4im]Cl2.implying that they had higher ability of lowing surface tension.The addition of sodium halides in the aqueous solution can decrease the cmc values and had an influence on the adsorption at air-water interface(Nal>NaBr>NaCl).Siloxane chain Gemini imidazolium surfactants had lower cmc than those of single-chain surfactants,which indicated that the Gemini series displayed stronger micelles formation ability.For Gemini imidazolium surfactants with same spacer group.[Si4CsSi4im]Cl2 series had higher efficiency and ability of lowing surface tension.stronger micelles formation ability,larger enthalpy driving force,micellar aggregation number and the aggregates size.For Gemini imidazolium surfactants with the same siloxane chain,the increase of spacer groups can enhance enthalpy driving force,and decrease the critical micelle concentration,micellar micropolarity,micellar aggregation number and the aggregates size.Besides,the siloxane chain Gemini imidazolium surfactants can form the larger aggregates.Based on the study of aggregation behaviors in aqueous solution for Gemini imidazolium surfactants and their siloxane derivatives,the effects of the dissymmetry,spacer group length and different hydrophobic group on the surface activity and the micellization process were obtained.The relevant results can be helpful for constructing relationship between molecular structure and property,which would be expected as the theoretical basis of molecular designing and application of new Gemini surfactants.