【作者】 刘国宇；

【导师】 丁伟；

【作者基本信息】 大庆石油学院 ， 油气田化学工程， 2010， 硕士

【摘要】 本文是在分子设计的基础上,针对课题组合成的系列烷基芳基磺酸盐类表面活性剂,利用分子动力学(MD, molecular dynamics)模拟这个最新方法研究其在水溶液或油水界面中的聚集形态,从而进一步探讨结构与性能的相互关系。程序分析结果表明,模拟的烷基芳基磺酸盐类表面活性剂性质与实验结果变化规律相符,可以从分子水平解释常规实验方法所观察不到的现象。采用分子动力学方法模拟不同质量分数的十二烷基苯磺酸钠、水体系,结果发现,在溶液浓度远高于临界胶束浓度的情况下,活性剂单体分子很少形成球状有序聚集体,而是随体系浓度的变化形成以蠕虫、棒状或网状为主的聚集体。采用分子动力学方法模拟3种自制的十四烷基芳基磺酸盐在真空和水溶液环境下的结构与相互作用,利用自由能微扰方法(Free Energy Perturbation,FEP)计算了水合自由能,发现与用传统热力学表面张力法测定自制的烷基芳基磺酸盐结果一致。研究表明:烷基芳基磺酸盐在水溶液中的胶束化过程是自发进行的,随着分子结构中芳环向长烷基链中间位置移动,胶束化能力和胶束的稳定性均下降;研究还发现,疏水基周围水分子的“冰山结构”会影响胶束的稳定性,而水分子中氢键的生存周期是反应冰山结构变化的重要指标;同时,亲水基与水分子间形成氢键的数目会增强或减弱分子脱离胶束体的趋势,从而影响胶束结构的稳定性。采用分子动力学方法模拟了”油水两相”分离过程及鸡蛋清溶菌酶(chicken egg-white lysozyme, HEWL)晶体对十二烷基苯磺酸钠的界面吸附行为的影响,考察了分子支化程度、浓度和不同油相在界面分离过程中的影响及作用。结果表明:对于油/水两相体系,在短时间内分离可达到平衡,形成一个明显的油/水界面;且在不同烷烃/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;随着溶液浓度的增大,界面吸附密度先增加然后略降,与实验变化规律相符;研究还提出,接触面积(ASA,accessible surface area)可以作为衡量表面活性剂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。HEWL晶体可以与活性剂形成形态复杂的复合物,从而影响表面活性剂降低油水界面张力的效果。更多还原

【Abstract】 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.更多还原