The Thermodynamic Study On The Aggregation Transition Of Surfactant Solutions

Surfactant solutions are widespread in daily life and production,and they are widely used in the fields of medicine,oil,daily washing etc..The controllable self-assembly of two amphiphilic surfactant molecules is one of the focuses in the field of colloid and interface chemistry.In this paper,cationic and anionic surfactants were used to form stable systems with different additives,and controllable micellar solutions were contructed by the intermolecular interactions.In this paper,the transformation of molecular aggregation state in micellar solutions was determined by the conductivity,rheological and thermal measurments.The kinetic and thermodynamic parameters were obtained.The ransformation mechanism and laws of the molecular aggregation state in aqueous solutions controlled by temperature were investigated systematically combined with NMR,electron microscopy and small angle X-ray scattering techniques,revealing the interaction mechanism between the molecules in the process of transition from the molecular level.It is of great significance to deepen the understanding of the law about the self-assembly of surfactants.This thesis is supported by the National Natural Science Foundation of China(No.21073081 and No.21473084),and the specific work is as follows:?.Study on the micelle transformation in pure solution system of single quaternary ammonium cationic surfactantThe change of aggregation state of quaternary ammonium cationic surfactant(CnTAB,CnHTAB,n=12,14,16)aqueous solution was studied.First and second critical micelle concentration(CMC1,CMC2)of six kinds of surfactants was determined by conductance method at different temperatures.The heat changes in the transformation process were measured by isothermal titration calorimetry and a series of thermodynamic parameters were obtained.Finally,the interaction between the head group of the surfactant and the environment around the head group in aqueous solutions of different concentrations was investigated by nuclear magnetic resonance(NMR)spectroscopy?.The thermodynamic study of aqueous two-phase system(ATPS)formed by anionic surfactant and imidazolium ionic liquid(IL)In this work,we demonstrate that the aqueous mixtures of ionic liquids(1-butyl-3-methylimidazolium tetrafluoroborate,[Bmim]BF4)and an anionic surfactant(sodium dodecy1 benzene sulfonate,SDBS)within a certain range of compositions can spontaneously separate into two immiscible phases: one surfactant-rich(upper)and the other IL-rich(bottom).At 298.15 K,the ternaty phase diagram of the system composed of1-butyl-3-methylimidazolium tetrafluoroborate([Bmim]BF4),sodium dodecy1 benzene sulfonate(SDBS)and water was drew by the visual and turbidity method.Samples of different compositions around the aqueous two-phase region in the three phase diagram were selected to perform the isothermal titration microcalorimetry(ITC)measurements,and the heat changes of the system with the addition of water were obtained.We can find that,with the increase of water in the sample,the calorimetric curve will show a less obvious endothermic and exothermic process,which is completely consistant with the formation and disappearance position of the aqueous two-phase in the phase diagram.This shows that ITC measurement is a feasible and effective method for the study of the aqueous two-phase system.?.Study on the phase behavior and temperature response characteristics of the mixed aqueous solution composed of single quaternary ammonium cationic surfactant and nonionic surfactantWe explored the phase behaviors of the ternary system containing cationic gemini surfactant 2-hydroxypropyl-1,3-di(tetradecyl dimethyl ammonium chloride)(14-3(OH)-14(2Cl))and nonionic surfactant polyoxyethylene laurel ether and determined the phase diagram.In several regions of the phase diagram phase,we have studied the region of temperature-response viscoelastic wormlike micellar solution.The focus of the study is the increase in viscosity of solution with increasing temperature and Brij-30 content.Rheological analysis was used to investigate the structural changes in different solutions and the factors affecting the growth of micelles.In addition,crygenic transmission electron microscopy(Cryo-TEM),small angle X-ray scattering(SAXS)and differential scanning calorimetry(DSC)were used to verify the above phase transition process.On the basis of the results obtained,the transformation mechanism of theaggregates was analyzed.