The Study On Aggregation Behavior Of Several Conventional Surfactants In PEG 200 And PEG 200/Water Mixed Solvents

Surfactant is a special kind of substance,which has both hydrophilic groups and lipophilic groups in its structure.It is widely used in the washing industry,food,skin care and pharmaceuticals.For a long time,surfactants rich self-aggregation behaviors have received widespread attention.In this paper,conventional anionic and cationic surfactants were used to form a stable system with non-aqueous solvent and mixed solvent of polymer and water.The thermodynamic and kinetic properties in the transformation of aggregate structure with varying the temperature,concentration and mixture ratio have been studied by macroscopic and microscopic methods.It not only enriches the study of the microstructure of surfactants in non-aqueous and mixed solvents,but also expands the application of such systems in the fields of synthetic chemistry,medicinal chemistry and daily chemistry.This thesis is supported by the National Natural Science Foundation of China(No.21473085),and the specific work is as follows:Firstly,the double hydrocarbon chain anion/cation mixed surfactant dodecyl dimethylammonium bromide and sodium Bis(2-ethylhexyl sulfonate)sulfosuccinate(AOT/DDAB)system was selected,which was easy to form a precipitate.The aggregation behavior of the mixed system in aqueous solution and polyethylene glycol 200(PEG 200)were studied by surface tension(ST),conductivity,fluorescence(Pyrene)and dynamic light scattering(DLS)at 298.15 K.Various methods have confirmed that the mixed system can self-assembly into the forward micelles in PEG 200.Compared with the water system,the critical micelle concentration(CMC)value in the PEG 200 system was increased by hundreds of times,and no precipitation occurs at any ratio.Observed from the values of the interaction parameter between the anion-cation surfactant,it is found that there are a strong attractive interaction and a synergistic effect between AOT and DDAB in aqueous solution,in comparison,the synergy between them in PEG 200 is very weak.Secondly,the micellization behavior of AOT in mixed solvent media of PEG 200 and water with varying mass fractions of PEG 200 has been studied by conductivity,isothermal titration microcalorimetry(ITC)methods.The effects of surfactant concentration,solvent composition and properties on surfactant aggregation behavior were investigated.The results showed that the mixed solvent can form micelles at any mixing ratio,and the CMC value increased with increasing PEG 200 amount.The values of the other two thermodynamic parameters((35)H_m~o and–T(35)S_m~o)indicated that the micelle formation was entirely entropy driven for the systems with pure water or high content of PEG 200(?80wt%).The other systems were driven by entropic as well as enthalpic contributions.Finally,the ratio of fixed mixed solvent,the transformation of gel-vesicle-micelle at the microscopic level was further verified by conductivity,rheological,transmission electron microscopy(Cryo-TEM)methods.Finally,the micellization behavior of dodecyldimethylethylammonium bromide(DEDAB)in mixed solvent media of EG,PEG 200,PEG 400 and water with varying temperature and mixed solvent ratio has been studied by conductivity,ITC and DLS methods.The results showed that the cosolvents with different chain lengths were added to the system,the three systems can form traditional surfactant aggregates.The CMC of DEDAB increased with increasing temperature,with the extent of the increase dependent on the decreased dielectric constant and“structure-breaking effect”of the cosolvent,it was not conducive to the micellization of the system.The effect of increasing the temperature and increasing the mass fraction of cosolvent in the mixed solvent on the formation of micelles was consistent.From a thermodynamic point of view,the addition of cosolvent made the Gibbs free energy of micellization((35)G_m~o)more positive than pure water.The values of the other two thermodynamic parameters(?H_m~o and-T?S_m°)indicated that the micelle formation of the three systems were driven by entropic as well as enthalpic contributions in the temperature range and mixed solvent ratio studied in this paper.In addition,the three cosolvent types have a slight effect on the CMC and thermodynamic parameters of the system.