Molecular Dynamics Simulation Of Sulphonate Surfactants At Oil/Water Interface

Sulphonate surfactants are the typical anionic surfactants, which can reduce the oil- water interfacial tension significantly. They are widely used in the enhanced oil recovery. Sodium dodecyl benzene sulfonate(SDBS) is a most common sulfonate surfactant, and it is chosed as the object in this paper. By changing the hydrophilic group and lipophilic group of SDBS, a series of s surfactants were designed. Molecular dynamics simulation method in MS was employed in the research of rules of oil/surfactant/water system interface properties and microcosmic mechanism under normal pressure and temperature.Firstly, molecular dynamics(MD) simulations were performed to investigate the adsorption behavior and microcosmic mechanism of oil-water interface, when linear alkyl benzene sulphonates which have different alkyl chains length were added to the system. Secondly, the combinated effects between oil phase and surfactants having different alkyl length were investigated on the properties of the interface. At the same time, the properties of the system when dodecyl sulfonates with different ring structure were added to the n-dodecane/water were explored. It was used to investigate the impact when the ring was in different place. At last, the adsorption behavior of bi-functional group surfactant which have sulfo group and carboxyl group were studied to discuss the interfacial properties of bi- functional group surfactant.The simulation result shows that sulphonate surfactants in oil-water interface can form a stable monolayer; the interface is a ‘transition zone’ with a certain thickness. According to the calculation of parameters such as interface formation energy, density distribution, thickness of interface, radial distribution, different influences and change rules were researched among sulfonate surfactants which have different structure in reducing oil- water interfacial tension theoretically. when the number of carbon atoms of alkyl chain of alkylbenzene sulfonate is 11 to 13, the alkylbenzene sulfonate has a good capability of hexadecath-water interfacial tension reducing; the alkyl chain with 12 to 14 carbon atoms of benzene sulfonate can reduce n-hexadecane/water interfacial tension better, dodecyl alkylnaphthalene sulphonate have a better capability of oil- water interfacial tension reducing when the alkyl chain and sulfonic group are located in the same benzene counterpoint, the double functional group surfactants which have sulfo group and carboxyl group can reduce dodecane-water interfacial tension better than the pure sulfonate surfactant.The simulation calculation provides theoretical guidance for the optimization and design of surfactants.