物理化学学报 >> 2010, Vol. 26 >> Issue (02): 422-428.doi: 10.3866/PKU.WHXB20100216

量子化学及计算化学 上一篇    下一篇

阴离子表面活性剂在水/正烷烃界面的分子动力学模拟

肖红艳, 甄珍, 孙焕泉, 曹绪龙, 李振泉, 宋新旺, 崔晓红, 刘新厚   

  1. 中国科学院理化技术研究所, 光化学转换与功能材料重点实验室, 北京 100190; 中石化胜利油田分公司地质科学研究院, 山东 东营 257001
  • 收稿日期:2009-09-29 修回日期:2009-12-01 发布日期:2010-01-26
  • 通讯作者: 肖红艳, 刘新厚 E-mail:hyxiao@mail.ipc.ac.cn; zhenz@mail.ipc.ac.cn

Molecular Dynamics Simulation of Anionic Surfactant at the Water/n-Alkane Interface

XIAO Hong-Yan, ZHEN Zhen, SUN Huan-Quan, CAO Xu-Long, LI Zhen-Quan, SONG Xin-Wang, CUI Xiao-Hong, LIU Xin-Hou   

  1. Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China; Institute of Geological Science, Shengli Oilfield Ltd. Co., Dongying 257001, Shandong Province, P. R. China
  • Received:2009-09-29 Revised:2009-12-01 Published:2010-01-26
  • Contact: XIAO Hong-Yan, LIU Xin-Hou E-mail:hyxiao@mail.ipc.ac.cn; zhenz@mail.ipc.ac.cn

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摘要：

利用分子动力学模拟方法研究了阴离子表面活性剂在水/正烷烃(壬烷, 癸烷和十一碳烷)界面的结构和动力学特点. 十六烷基苯磺酸钠作为研究对象, 其中苯磺酸基团在十六碳烷的第4号碳原子上, 记作4-C16. 分析了不同油相和特定盐度条件下正烷烃-表面活性剂-水体系的界面特点(如密度剖面图、界面张力和径向分布函数). 模拟结果表明平衡模型体系展现了一个很好的水/正烷烃界面. 当加氯化钠到水溶液中, 正烷烃-表面活性剂-水体系的界面张力有微小的变化, 有趣的是表面活性剂二面角的反式结构分数的变化联系着界面张力的微小变化. 可见, 表面活性剂在界面处的结构对降低界面张力起到重要的作用. 此外, 还发现表面活性剂的极性头与钠离子和水分子存在较强的相互作用.

关键词: 分子动力学, 水/正烷烃界面, 阴离子表面活性剂, 界面张力, 反式结构分数

Abstract:

The structural and dynamic properties of anionic surfactant at the water/n-alkane (nonane, decane, and undecane) interface were investigated by the molecular dynamics simulation. The model anionic surfactant contained a benzene sulfonate group attached to the 4th carbon in the hexadecane backbone and was denoted as 4-C16. We analyzed the interfacial properties (density profile, interfacial tension, and radial distribution function) of the n-alkane-surfactant-water systems in different oil phases and under special inorganic salinity conditions. The simulation results indicate that a well-defined interface exists between the n-alkane and water phases in the equilibrated model systems. The interfacial tensions of the n-alkane-surfactant-water systems show little change when sodium chloride is added to the solutions. We find that a change in the trans-form fraction of the dihedral in 4-C16 is related to a subtle change in the interfacial tension at the water/n-alkane interface. Clearly, the structure of the surfactant at the interface plays an important role in reducing the interfacial tension. In addition, we also find that the polar head group of the surfactant molecules with sodiumions and water molecules undergo stronger interactions.

Key words: Molecular dynamics, Water/n-alkane interface, Anionic surfactant, Interfacial tension, trans-formfraction