表面活性剂界面吸附行为的分子动力学模拟

Molecular Dynamics Simulation of Anionic Surfactant Aggregation at the Interface

采用分子动力学(MD,Molecular dynamics)方法模拟了油、水两相分离过程及表面活性剂十二烷基苯磺酸钠在油-水界面的吸附行为,考察了十二烷基苯磺酸钠分子支化程度、在油-水体系中的浓度和不同油相对油、水两相分离过程的影响及作用。结果表明,对于油-水体系,油、水两相在短时间内可达到分离平衡,形成一个明显的油-水界面;在烷烃-水体系中,以十二烷作为油相时,十二烷基苯磺酸钠在界面处浓度最大,吸附趋势最强;随着体系中十二烷基苯磺酸钠浓度的增大,模拟得到的吸附峰值浓度先增加然后略降,与实验结果相符。表面活性剂的界面接触面积(ASA,accessible surface area)可以作为衡量表面活性剂的油-水界面吸附能力及电解质降低油-水界面张力效果的指标。MD给出的分子水平的微观信息可以为三次采油技术中表面活性剂的筛选及有效应用提供指导。

The separation process of oil-water and the properties of sodium dodecyl benzene sulfonate adsorbed at the water-oil interface were investigated by using molecular dynamics（MD） simulations on a molecular level,considering the variation of molecular structure and the concentration of sodium dodecyl benzene sulfonate in oil-water system,and the oil phase type.The result showed that the oil and water phases reached equilibrium in a short simulation time and an evident oil-water interface was formed.In the alkane-water system,as the alkane is dodecane,the sodium dodecyl benzene sulfonate had the largest interface distribution density and the most trend of absorption to the interface.The maximum adsorption concentration in the oil-water interface was increased with the increase of surfactant concentration first,then slightly descended.These simulation results were consistent with the experimental results.At the same time,the accessible surface area of surfactant could be used to measure the adsorption capacity and the effect of electrolyte on the interfacial tension at oil-water interface.MD method helps to enhance the understanding of the surfactant action in oil-water system and to guide screening of surfactants in tertiary oil recovery technology.