分子动力学模拟钙离子影响SB12-3/SDBS复配体系的油/水界面聚集行为

Effect of Ca2 on Aggregation Behavior of Anionic/Zwitterionic Surfactant Mixed System at Oil/Water Interface：A Molecular Dynamics Study

摘要:

本文采用分子动力学模拟对十二烷基磺丙基甜菜碱（SB12-3）/十二烷基苯磺酸钠（SDBS）表面活性剂复配体系在油/水界面的聚集行为进行了研究，在分子水平上讨论了Ca2 对SB12-3/SDBS表面活性剂复配体系两亲性质的影响。模拟结果表明， SB12-3与SDBS的配比为4:6时两者的协同增效作用最好。Ca2 加入后可以取代油/水界面处Na 的位置，压缩SB12-3和SDBS的极性头基使两者在油/水界面排布的更紧密。径向分布函数表明，Ca2 存在时SB12-3和SDBS中的-SO3-与水分子的相互作用增强，Na 更加靠近SB12-3的-SO3-，使其扩散双电层被压缩；同时，SB12-3和SDBS的溶剂可及面积明显减小，使两者在界面排布的更紧密。通过计算疏水尾链序参数以及SB12-3和SDBS的极性头基与疏水尾链之间的角度，发现Ca2 可以使SB12-3和SDBS的疏水尾链与油相的相互作用增强，降低油/水界面张力。

Abstract:

The aggregation behavior of N-Dodecyl-N, N-Dimethy–3–Ammonio–1– Propanesulfonate(SB12-3)/sodium dodecyl benzene sulfonate(SDBS) surfactant mixed system at oil/water interface was studied by molecular dynamics simulation. The effects of Ca2 on the amphipathic nature of SB12-3/SDBS surfactant mixed system were investigated at the microscopic point of view. The simulation results showed that SDBS and SB12-3 exhibited the best synergistic effects as the proportion of them reached 4:6. Ca2 replaced the position of Na at the oil/water interface, and compressed the headgroups of SB12-3 and SDBS so that both the surfactants were arranged more closely at oil/water interface. Radial distribution function indicated that the interaction between -SO3- in SB12-3 and SDBS and water molecules increased with the addition of Ca2 , Na were closer to -SO3- in SB12-3, and the thickness of electric double layer was compressed. The solvent accessible surface areas also declined obviously when Ca2 existed in the solution. By calculating order parameter and angles between the hydrophilic groups and hydrocarbon chains of SDBS and SB12-3, it was found that Ca2 could enhance the interaction between decane and hydrocarbon chains of SB12-3 and SDBS, and reduce the oil/water interfacial tension.