Synthesis And Properties Of Dendritic Cationic Oligomeric Surfactants

The special structure of oligomeric surfactant endows them the superior solution properties. Compared with the traditional single surfactants, the surface active of oligomeric surfactants is higher and the value of cmc is lower. Oligomeric surfactants aqueous solution has a special phase behavior and rheological property, which make them have a very broad application prospects. For now, the focuses of people are almost putted on the quaternary ammonium dimeric surfactants, but the reports about trimeric, tetrameric or polymeric surfactants are much fewer. Taking the structure characteristics of the traditional surfactant as the starting point, reference method for the synthesis of dendrimers polyamidoamine, we got a series of trimeric and tetrameric surfactants with N, N’-dimethyl-1,3-propanediamine and2-hydroxy-1,3-propane diamine as the core respectively. The number of carbon atoms in each hydrophobic chain for two series of surfactants is12,14and16respectively. The series of trimeric surfactants are named as TRQ-C12TRQ-C14TRQ-C16,and the series of tetrameric surfactants are named as TEQ-C12、TEQ-C14、 TEQ-C16.The surface activities of surfactants are studied by the surface tension. Results showed that oligomeric surfactants have much higher surface activity than traditional surfactants. Effects of the hydrophobic chain length and inorganic salt on the cmc value are reseached.(1)When the hydrophobic chain number are certain, longer the surfactant hydrophobic chain are, smaller cmc values are.(2) The addition of inorganic salt increased the number of counterions in solution, weakens the electrostatic repulsion between ionic head groups of surfactants, the more easily the formation of micelles.In the experiment of micro polarity of micelles by steady-state fluorescence of pyrene probe, the smaller value of11/13indicates that the nonpolarity of microenvironment of pyrene molecules is stronger. We got the micellar aggregation number by fluorescence quenching.With the increase of the length of hydrophobic chain, the surfactant micelle aggregation number also showed a rising trend. Micelle aggregation numbers of oligomeric surfactant are much lower. With the increase of the length of hydrophobic chain, Hydrophobic interaction in solution become stronger. Therefore, several surfactant moleculars associate and can form micelles at low surfactant concentration.The size and distribution of different concentration of surfactant micelles can be seen clearly by dynamic light scattering experiments. Experiments prove that the surfactant in low concentration start to form large size spherical aggregates. When above a certain concentration, hydrophobic interaction becomes stronger, forcing the surfactant hydrophobic chain closer together, forming a cone shape molecular structure.The aggregation was changed from large size spherical structure into small size spherical micellar.