| A new trimeric quaternary ammonium surfactant , citric triesters of tri ( dodecyldimethyl-2-hydroxypropane ) ammonium chloride (CTTAC) ,was synthesized by citric acid , epoxy chloropropane and dodecyl dimethyl amine in the presence of isopropanol as solvent. The yield of CTTAC is above 90% while reaction time is 12h, temperature 85℃, molar ratio of n(citric acid): n(dodecyl dimethyl amine): n(epoxy chloropropane)is 1.00 : 3.00: 3.05. The effects of temperature, reaction time and the molar ratio of the reactants on the yield of CTTAC have been studied respectively. The structure was characterized by IR spectrum, H' -NMR and elementary analysis. The mechanism of the reaction is investigated.The absorption parameters cmc, γcmc, Γ, A of CTTAC were characterized by means of surface tension at the air/water interface and compared with monomeric, dimeric, trimeric quaternary ammonium surfactant obtained from literature. In addition, a new model to detrmination of the ionization degree of three head and three hydrophobic chain ionic surfactant micelle was established by conductivity measurement. The ionization degree of CTTAC was determined by the model and compared with the values drew from empirical method.Aggregation numbers of micelle of CTTAC were determined by steady-state fluorescence probe method in which pyrene was used as fluorescence probe and cetylpyridinium chloride(CPC) as quencher. Satisfactory results were obtained when the solution of surfactant was prepared with saturated aqueous solution of pyrene and the concentrations of CPC were selected in 0.1-0.3 mmol·L-1.The experimental results show that aggregation number(N)increases linearly with the increase of CTTAC concentration in the range of 610 times of cmc and critical micellar aggregation number Nm can be extrapolated from N-c curve.N=1.1867ccitac+11.7500From I1/I3c(CTTAC),critical micelle concentration(cmc) was also determined by steady-state fluorescence probe and agree better with the value determined by surface...
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