Morphological Tuning And Mechanism Study Of The Self-Assembly Of Cationic Surfactants

Surfactant can from a variety of morphologies spontaneously because of its unique molecular structure,and these morphologies will be advantageous for practical applications depending on the nature of the various morphologies,such as,vesicles can serve as the intermediary of carrying drugs,worm-like micelles can be used to improve the viscoelasticity of surfactant solution and has been used in the cleaning fracturing fluid.If the further study of the self-assembly mechanism of surfactant can be paid more attention,we will use surfactant more freely.However,the research on the self-assembly mechanism of surfactant is weak,and in determining the essential information of the surfactant micelle,such as molecular arrangement and interaction,is still experimentally challenging.In this thesis,we adopt coarse-grained molecular dynamics simulation(CGMD)to study the self-assembly of cationic surfactant in different surfactant concentration,different salts,and different proportion of mixed surfactant.Surfactant micelle morphology and size will vary as the change of its concentration.In our work,we got a series of different shape and different size micelles by changing the concentration of the surfactant CTAC.With the increase of concentration,we got spherical micelles,rod-shaped micelle,worm-like micelles in order.Ionic surfactant micelle are charged body,the electrostatic interaction distance in different surfactant concentration is the reason why the micelles can't fusion.If there are some salts in the urfactant system,the surfactant consumption can be reduced effectively,and at the same time,we can get the same configurations which can be formed under higher concentration.In this work,we studied the effect of different salts(organic salt NaSal and inorganic salt NaCl)and different salt concentration on the surfactant self-assembly,we found that,the morphology is more rich in the surfactant system which was added NaSal than that in added NaCl system,it is the different participant modes between NaSal and that lead to this result.NaSal can be embedded into the micelle,but NaCl can't.Mixtures which are composed of two or more surfactants have the properties that a single type of surfactant can't be obtained,and the self-assembled morphologies are more rich than single surfactant system.In our thesis,coarse-grained molecular dynamics simulation was carried out to study the micelles formation in a cationic cetyltrimethylammonium chloride(CTAC)and anionic sodium dodecyl sulfate(SDS)system.In the mixtures,as the mixed ratio changed,a series of morphologies was obtained than the system added salt,such as dis-like micelle,vesicle.When the ratio of SDS was equal to that of CTAC,a vesicle was formed by disk-like bilayer curling and the entropy was the driving force.In this paper,we make full use of the advantages of coarse-grained molecular dynamics simulation which can study large-scale systems and provide microscopic details,and it makes up for shortcomings on the experiment,at the same time,this study bright to a new light for a further understanding of the microscopic mechanism of surfactant self-assembly.