季铵盐对表面活性剂自组装行为的分子动力学研究

发布时间：2018-07-11 14:11

本文选题：TAADS + 分子动力学　；参考：《山东大学》2017年博士论文

【摘要】：季铵盐型TAADS表面活性剂体系由于其特殊的性质,在工业和生活中具有重要的应用。实验发现以TAA+为反离子的表面活性剂体系比传统的无机离子为反离子的表面活性剂体系具有更好的溶解性,而且当抗衡离子体积比较大时(如TBADS体系)会出现浊点现象。实验工作者提出多种TAADS体系微观胶束结构,用来解释这种实验现象,包括用TBADS胶束之间的桥连模型,解释类似体系的浊点现象。实验也发现TAADS对泡沫的稳定性同样也有很大的影响,因此理解TAADS在气液界面的微观结构同样具有重要的意义。虽然实验上对上述实验现象给予了充分关注,但是微观结构模型仍然没有统一结论。分子动力学模拟作为实验上的一种有效辅助手段,可以在分子水平上对所研究体系进行微观结构和动力学性质的研究,因此利用分子动力学方法也是解决TAADS相关体系一系列实验问题的有利工具。本论文围绕TAADS体系通过分子动力学的方法主要展开了一系列如下的研究:(一)通过分子动力学的方法对于TAADS体系的相关性质进行了系统的研究,首先是TAADS体相的聚集行为,主要包括胶束的大小、形状,表面极性头的分布,内部尾链末端碳的分布,表面活性剂分子不同位置的水化数,以及表面活性剂分子和抗衡离子的结合方式等方面。结果表明胶束的半径大小存在TMADSTEADSSDSTPADSTBADS的顺序。模拟也表明烷基尾链上的一些亚甲基和末端C位于胶束的极化层。极性头和抗衡离子存在四种结合方式,其中两个TAA+尾链插入到DS-形成的胶束表面而形成混合胶束,此种方式是最多的结合模式。根据上述模拟理论,我们提出了分子水平上相关体系的动力学模型。模拟结论支持前人实验上提出的EPR/TRFQ模型,是对实验上所提模型的进一步验证和细化完善。分子动力学模拟研究了 TAADS在气液界面上的结构特征,主要包括表面吸附膜的不同原子Z方向的概率分布、极性头和抗衡离子的结合方式、吸附层第一水化层的吸附特征、尾链有序参数、以及弱氢键等。研究表明TAA+抗衡离子对表面活性剂极性头的第一水化层有很大的影响,主要在于使得第一水化层的水分子数目变小。同时,TAA+抗衡离子和极性头之间形成了弱氢键,这些弱氢键限制水分子的运动。通过模拟发现极性头和抗衡离子通过四种结合方式形成混合吸附层,其中第二种结合方式(抗衡离子TAA+两个尾链插入到DS-形成的单层吸附表面从而形成混合吸附层)占据主导。利用分子动力学模拟,得到了 TAADS的气液界面上的吸附层的微观结构特征。最后通过模拟对TBADS和TBAC体系的异同进行了详细的研究,主要包括二者在不同温度下的解离度、极性头和抗衡离子之间的结合方式、抗衡离子的吸附自由能、以及胶束之间的动力学行为和相互作用等。研究发现TBAC体系中TBA+离子的解离度高于TBADS体系的,但是温度对解离度的影响是很小的。模拟表明极性头的构型和电荷的差异能够影响TBA+离子和胶束间的结合方式。本文同时研究了 TBADS胶束之间的桥连模型并从微观水平上得到了其具体的结构。研究结果表明两层TBA+抗衡离子桥连的DS-胶束构型是最稳定的。(二)用QH方法重点研究了 SDS胶束化过程中表面活性剂构型熵的变化,其中包括平动熵、转动熵和振动熵的变化以及它们所占的比例。依据计算结果对胶束化过程中熵的来源给予了具体的解释。研究结果表明胶束化过程中表面活性剂分子平动熵的变化是很小的,这一点可以很好的解释实验上发现的胶束和周围环境的表面活性剂分子的交换现象。同时发现胶束化过程中熵的增加来自于水分子熵的增加和表面活性剂分子构型熵的减小两部分,其中水分子熵的增加占主导。最后重点介绍了 HSMD方法的基本原理和程序的编写,以实现HSMD方法求熵。基于得到的轨迹以及程序的改进,计算了 SDS胶束化熵的结果,与QH计算的结果作对比。HSMD方法的研究为将来研究复杂体系和探索新方法打下了基础。
[Abstract]:The quaternary ammonium salt TAADS surfactant system has an important application in industry and life because of its special properties. It has been found that the surfactant system with TAA+ as the reverse ion has better solubility than the traditional inorganic ion surface active agent system, and when the counterion volume is relatively large (such as the TBADS body) A variety of TAADS system micro micelle structures are proposed to explain this experimental phenomenon, including the model of bridging between TBADS micelles to explain the cloud point phenomenon of the similar system. The experiment also found that TAADS also has a great influence on the stability of the foam. Therefore, it is understood that the TAADS is in the gas liquid interface. The observation structure is also of great significance. Although the experiment has given full attention to the experimental phenomena, the microstructure model still has no unified conclusion. As an effective auxiliary means of the experiment, the molecular dynamics simulation can study the microstructure and dynamics properties of the system at the molecular level. The use of molecular dynamics is also a useful tool for solving a series of experimental problems in TAADS related systems. In this paper, a series of studies have been carried out around the TAADS system through molecular dynamics methods: (1) a systematic study of the related properties of the TAADS system through molecular dynamics, first of all, TAADS The aggregation behavior of the body phase mainly includes the size, shape, distribution of the surface polar head, the distribution of carbon at the end of the internal tail chain, the number of hydration of the surfactant molecules in different positions, and the binding mode of the surfactant molecules and the counterions. The radius of the surface of the gelatin bundle exists in the order of TMADSTEADSSDSTPADSTBADS. The simulation also shows that some methylene and terminal C on the alkyl tail chain are located in the polarization layer of the micelle. There are four binding modes of polar head and counterion, of which two TAA+ tail chains are inserted into the micellar surface formed by DS- and form mixed micelles. This method is the most binding mode. According to the above simulation theory, we have proposed molecular level. The simulation results support the EPR/TRFQ model proposed by predecessors and further verify and refine the experimental model. The molecular dynamics simulation studies the structural characteristics of TAADS on the gas liquid interface, mainly including the probability distribution of the different atomic Z directions of the surface adsorption membrane, the polar head and the polar head. The binding mode of the ions, the adsorption characteristics of the first hydration layer of the adsorption layer, the order parameter of the tail chain, and the weak hydrogen bond. The study shows that the TAA+ counterions have a great influence on the first hydration layer of the surface active agent, mainly because the number of water molecules in the first hydration layer becomes smaller. At the same time, the TAA+ counterbalance ion and the polar head. The weak hydrogen bonds are formed. These weak hydrogen bonds restrict the movement of water molecules. Through the simulation, the polar head and counterions are found to form a mixed adsorption layer through four binding modes, of which second kinds of binding methods (the two tail chains of the anti ion TAA+ are inserted into the monolayer adsorbed surface formed by DS- to form a mixed adsorption layer) dominate. The microstructural characteristics of the adsorption layer on the gas-liquid interface of TAADS are obtained by mechanical simulation. Finally, the differences and similarities between the TBADS and TBAC systems are studied in detail, including the dissociation degree of the two at different temperatures, the binding mode between the polar head and the counterions, the adsorption free energy of the counterions, and the micelles. It is found that the dissociation degree of TBA+ ions in the TBAC system is higher than that of the TBADS system, but the effect of temperature on the degree of dissociation is very small. The simulation shows that the difference in the configuration and charge of the polar head can affect the binding mode between the TBA+ ions and the micelles. The bridge connection between the TBADS micelles is also studied in this paper. The model has obtained its specific structure at the micro level. The results show that the DS- micelle configuration of the two layer TBA+ counterbalance ion bridge is the most stable. (two) the changes in the configuration entropy of the surface active agent in the SDS micellization process are studied by QH method, including the change of the translational entropy, the change entropy and the vibration entropy and the ratio of their ratio. A specific explanation is given to the source of entropy in micellization according to the calculation results. The results show that the change of the molecular translational entropy of the surface active agent in the micellization is very small, which can explain the exchange phenomenon of the surfactant molecules of the micelles and the surrounding environment. And the micellization is also found. The increase of entropy in the process comes from the increase of water molecular entropy and the decrease of two parts of the molecular configuration entropy of surface active agent, in which the increase of water molecular entropy is dominant. Finally, the basic principle of HSMD method and the programming of the program are introduced in order to realize the entropy of HSMD. Based on the track track and the improvement of the program, the SDS micellization is calculated. The result of entropy is compared with the result of QH calculation. The research of.HSMD method lays a foundation for future research of complex system and exploration of new methods.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O647.2

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