Molecular Dynamics Simulation Of The Congeries Of Alkylbenzene Sulfonate In Aqueous Solution

In this paper, the aggregation of alkyl benzene sulfonates in water and oil interface were studied by molecular dynamics. Then, the structure and the dynamic properties of these systems were discussed from molecular scale. The analysis of program can explain and predict some results and phenomena of experiments and provide approaches of theoretical directive for further study of these systems.Some surfactant/water systems were investigated by MD. We founded that the aggregation morphology are divided into several structures , such as sphere micelle, mixed micelle of sphere and rod, rod micelle and lamellar phase. However, with the increase of surfactant concentration, the monmeric surfactant can hardly become the sphere micelle.In order to investigate the influence of the molecular structure of surfactants on the micellization in solution, we used a molecular dynamics method and simulated the molecular structure and interaction of three alkyl aryl sulfonates in the vacuum and solution. The solvation free energy was calculated from free energy perturbation (FEP), and the result was consistent with that using surface tension method. Research show that the micellization of alkyl aryl sulfonate in aqueous solution is a spontaneous process, as the aromatic ring shift from the edge to the middle of the long carbonic chain, the formation ability of micelle and the micelle stability is decreased; the changes of"iceberg structure"which around hydrophobic groups and among the water molecules may affect the stability of the micellization, and lifetimes of hydrogen bonds were used to research the"iceberg structure"; at the same time, it was found that numbers of hydrogen bonds between hydrophilic groups of alkyl aryl sulfonates and water molecules can improve the decomposition trend of micellization, and affect the stability of micellization.The separation process of oil/water and the properties of sodium dodecyl benzene sulfonate and chicken egg-white lysozyme(HEWL) adsorbed at the water/oil interface, has been investigated on a molecular level by considering the variation of structure, interfacial and concentration using molecular dynamics simulations. The result found that:the two oil/water phases reached equilibrium in a short simulation time and an evident oil/water interface was formed; In the alkane/water system, as the dodecane is used to the oil, the surfactant had the biggest interface distribution density and the trend of absorbed to the interface; The adsorption density which were increased with the concentration of surfactant, then, slightly descended in the interface. These were consistent with the experimental results. At the same time, the accessible surface area(ASA) of surfactant could measure the adsorption capacity and the effect of electrolyte to the interfacial tension at oil/water interface. The HEWL-sodium dodecyl benzene sulfonate compounds at the water/oil interface can affect the interfacial tension.