Study On The Assembling Behavior In Water Phase And Adsorption Behavior At Solid/Water Interface Of Ionic Surfactants

In this thesis, conductivity and fluorescence spectroscopy were used to study the assembling behavior of ionic surfactant sodium dodecylbenzene sulfonate (SDBS) and cationic surfactant cetyltrimethylammonium bromide (CTAB) in water, meanwhile the adsorption behavior of these two surfactants on clay kaolinite/water interface was investigated using solution concentration difference method. Also, the effect of salt concentration and especially polymer PVP were considered. It was found that SDBS and CTAB molecules can self-assemble with increasing concentration, transfering from monomers to micelles at concentrations above critical micelle concentration (CMC). The CMC of SDBS and CTAB in pure water are1.50mmol/L and0.89mmol/L respectively, while they decrease to0.90mmol/L and0.56mmol/L, respectively at the present of0.01mol/L NaCl, which suggests that NaCl can promote their micelles formation. PVP (0.1g/L) is proposed to change the assembling process of SDBS and CTAB which turned out to transfer from monomers to surfactant/polymer micelles then to free micelles. Critical aggregate concentration CAC of SDBS and CTAB are1.50mmol/L and0.25mmol/L, respectively, and CMC of them are5.50mmol/L and1.25mmol/L, respectively.The adsorption results show that SDBS and CTAB adsorbed onto kaolinite. The pseudo-second-order kinetic model better fits for the adsoption process of SDBS and pseudo-first-order adsorption kinetic model better fits for CTAB, which mean adsorption process of SDBS is controlled by chemical adsorption, while the adsorption of CTAB is mainly controlled by physical adsorption. Structures of the adsorbed layer of SDBS and CTAB are multilayer with compiled micelles. Adsorption isotherms of these surfactants can be better fitted to a general isotherm model, and their adsorbed morphologies on kaolinite include monomers, hemimicelles and micelles. When NaCl and PVP coexisted, NaCl raised the adsorption quantities of of SDBS and CTAB, while PVP to some extent hindered adsoption quantaties of them.Comparising the assembling behavior and adsorption behavior of SDBS and CTAB, It was found that micelles have appeared in above two processes and the concentration forming these two kind micelles are very close.