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离子型表面活性剂分子在十六烷/水乳液内界面的吸附动力学研究
杨方源
学位类型博士
导师王富
2017-05-28
学位授予单位中国科学院大学
学位授予地点北京
学位专业材料物理与化学
关键词水-油界面 乳液 表面活性剂 电迁移率 Zeta电位 二次谐波
摘要

研究表面活性剂分子与水-油界面的相互作用,对理解含油污水处理过程中涉及的水-油体系稳定机制至关重要。本论文主要使用具有界面选择特性的二次谐波(SHG)技术,结合Zeta电位表征,研究表面活性剂分子在水-油弯曲界面的吸附动力学过程。第一部分为理论模拟部分。通过理论计算得出基于Gouy-Chapman模型和O’Brien-White方法能够解释电迁移率和电位与离子强度的依赖关系出现极大值的现象,借助O’Brien-White方法计算了电位随着离子强度变化的关系,并通过反推电迁移率的值得到了电位的值,解释了离子强度对界面电势的影响。在特定限制条件下(例如离子半径较小,电迁移率的值较低),通过O’Brien-White公式计算的电位的结果会影响离子强度的曲线,但是在另外一些限制条件下(粒子半径较大且电迁移率的值也较高),电迁移率和电位随着离子强度变化的曲线很相近。将电迁移率与和电位与离子强度依赖关系之间出现极大值的理论计算值与实验数值比较分析,阐述了离子效应对电位变化的具体影响。第二部分主要研究了阴离子表面活性剂十二烷基硫酸钠(SDS)在乳液界面吸附过程。首先实验检测了十六烷乳液的电迁移率在不同离子强度下随着体系pH值和SDS浓度变化的规律。实验中观察到电位是否出现极大值依赖于体系参数。同时结合十六烷-水界面的SHG实验和Zeta电位实验推测了阴离子表面活性剂SDS在界面的分子结构和吸附过程。研究结果为分子层次上进一步丰富和完善界面双电层理论提供了实验和理论支持。第三部分为阳离子表面活性剂分子在乳液界面吸附过程的研究。这部分工作通过借助SHG技术和Zeta电位手段探测了探针分子D289在含有阳离子表面活性剂的乳液上的吸附行为。考察的阳离子表面活性剂包括Bola、LTAB、Gemini、和DDAB分子。SHG实验结果表明,Bola型分子在乳液表面吸附时与其他几种阳离子分子之间的信号有明显差异,并且通过D289分子在乳液界面的吸附密度可以来解释此差异性。研究结果表明竞争吸附和尾链之间的相互作用对表面活性剂分子在乳液表面的吸附过程有重要作用。同时,这一研究也表明了表面活性剂分子的构型对吸附动力学行为有重要影响。第四部分为两性表面活性剂分子在乳液界面的吸附过程的研究。实验选取了两种两性表面活性剂分子,一种是头基外侧带正电的表面活性剂分子NPC16,另一种是头基外侧带负电的表面活性剂SNC16,实验结果表明,两种两性表面活性剂分子在水油乳液表面的吸附行为有一定的差异,但是差异并不显著。总体上来说,NPC16分子比SNC16分子更容易吸附在乳液表面。综上所述,本论文将SHG方法和Zeta电位测量方法相结合,研究了阴离子、阳离子、两性表面活性剂分子在乳液界面的吸附动力学过程,为明确表面活性剂分子在界面的吸附行为提供了理论和实验指导,同时为从分子层次理解其他界面吸附过程的机理提供了一种简便、灵敏的方法。

其他摘要

Studying the effect between the surfactants and water-oil interfaces is crucial for understanding the stability of water-oil mixtures which significantly influences the water-oil separation process. This thesis mainly focuses on investigating the adsorption dynamics of surfactant molecules at the interfaces of hexadecane-water emulsion utilizing surface-sensitive Second Harmonic Generation (SHG) technique and zeta potential measurements.The first part is about the theoretical simulation. It was also pointed out that the O’Brien-White approach based on the Gouy-Chapman model could be used to understand the maximum in electrophoretic mobility curves as a function of ionic strength and lead to understandable zeta potential curves. In this part we report our simulation on the ionic strength dependent zeta potential curves based on the O’Brien-White approach. We obtained the value of zeta potential which is inversed deduction from the value of electrophoretic mobility, which can interpret the influence of ionic strength on surface potential well. In some cases (such as the small particle radius and low value of mobility), the simulation shows that the calculation based on the O’Brien-White approach does change the trend in the concerned ionic strength dependent curves. However, the simulation in some other cases (such as the large particle radius and high value of mobility)also leads to similar trends in the ionic strength dependent electrophoretic mobility curves and zeta potential curves.The second part depicts the study on the dynamic process of anion surfactant SDS at the interface of hexadecane-water emulsions. We present the experimental results of the ionic strength dependent electrophoretic mobility of the hexadecane droplets in the hexadecane-water emulsions at different pH or in the presence of sodium dodecyl sulphate (SDS) at varied concentrations. In the experiments, both the existence and non-existence of such a maximum phenomenon were observed and demonstrated to be system dependent. The corresponding molecular structure of the oil-water interface was then discussed based on the analyses of the zeta potential curves combined with second harmonic generation signals recorded at the hexadecane-water interface. This work provides theoretical and experimental information for further understanding on the electric double layer theory.The third part describes the results on the dynamic process of cation surfactants at the interface of hexadecane-water emulsions. This work probe the adsorption behaviors of 4-(4-diethylaminostyry) -1-methylpyridinium iodide (D289) on the oil droplet surface in hexadecane-water emulsion in the presence of cation surfactants by second harmonic generation technology and zeta potential measurement. The surfactants include Bola, LTAB, Gemini and DDAB. The SHG results showed that the SHG signal from the emulsion with Bola molecule was distinct from that from the emulsion with LTAB, Gemini and DDAB, which could be explained by the adsorption densities of D289 molecule at oil droplet surface with various surfactants. The results revealed that both the competition adsorption and charge-charge interactions played important roles to the behaviors of surfactants at the emulsion interface. This study sheds new light to illustrate the influence of surfactant molecule geometry on the adsorption kinetics to droplet surface.The last part focuses on the dynamic process of zwitterionics surfactants at the interface of the hexadecane-water emulsions. The adsorption manifests slight difference between the two zwitterionics surfactants(NPC16 and SNC16) at the interface of hexadecane-water emulsion. Overall, the adsorption of the NPC16 with the outside part of head group positive is more easily than that of the SNC16 with the outside part negative at the interface of hexadecane-water emulsion. In conclusion, this thesis studies the dynamic processes of anion, cation and zwitterionics surfactants at the interface of hexadecane-water emulsions by SHG and Zeta potential methods. The results provide both theoretical and experimental information for further understanding on the adsorption behaviors of surfactants at the emulsion interface and are hopeful to be applied in understanding the molecular mechanisms of many other interfacial processes.

文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/4938
专题环境科学与技术研究室
作者单位中国科学院新疆理化技术研究所
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杨方源. 离子型表面活性剂分子在十六烷/水乳液内界面的吸附动力学研究[D]. 北京. 中国科学院大学,2017.
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