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离子型表面活性剂的界面吸附动力学与分子链长关系的二次谐波研究
梁远振
学位类型硕士
导师贾汉忠
2018-05-25
学位授予单位中国科学院大学
学位授予地点北京
学位专业材料工程
关键词二次谐波 十六烷-水界面 离子表面活性剂 链长 吸附自由能
摘要

表面活性剂的性质、界面的性质以及溶剂的组成和性质对表面活性剂在界面的吸附速率、结构和浓度有很大的影响。本论文主要使用灵敏的具有界面选择性的二次谐波光谱(SHG),研究了离子型表面活性剂在十六烷-水界面的吸附动力学过程。第一部分通过SHG方法系统地研究了不同链长阳离子表面活性剂三甲基丙基溴化铵(C3TAB)、己基三甲基溴化铵(C6TAB)、辛基三甲基溴化铵(C8TAB)和十二烷基三甲基溴化铵(C12TAB)在十六烷-水界面上的吸附过程。通过Langmuir吸附模型拟合得到各种阳离子表面活性剂在十六烷-水界面的吸附自由能,进一步通过吸附自由能与链长的拟合得到阳离子表面活性剂在十六烷-水界面上每个亚甲基的吸附自由能。该值小于文献报导的表面活性剂在空气-水界面上的每个亚甲基的吸附自由能,得到了十六烷-水界面上表面活性剂之间的链-链相互作用弱于空气-水界面上的链-链相互作用的结论。这为表面活性剂吸附到界面上的驱动力的来源提供了另一种解释。后续研究得到的不同链长阳离子表面活性剂脂肪胺CnNH2(n=10,12,14,16,18)在十六烷-水界面的吸附自由能随链长的变化并没有规律地改变,这可能与脂肪胺在界面上的解离是否完全以及胺基头基与水分子之间氢键结构有关。第二部分通过SHG方法系统地研究了不同链长阴离子表面活性剂十酸(C9COOH)、十二酸(C11COOH)、十四酸(C13COOH)、十六酸(C15COOH)和十八酸(C17COOH)在十六烷-水界面上的吸附过程。研究发现表面活性剂吸附自由能的绝对值随着烷基链的增长而增加。通过线性拟合得到这些表面活性剂从油相吸附到十六烷-水界面的过程中每个亚甲基的吸附自由能。所得结果与前述阳离子表面活性剂从水相吸附到界面时每个亚甲基的吸附自由能基本相同。这表明相对于疏溶剂作用,表面活性剂之间的链-链相互作用是吸附驱动力的主要贡献。实验发展了利用二次谐波技术测量头基基团吸附自由能的方法,同时也提供了一种测量其它油溶性表面活性剂头基溶解能的方法。此外,本部分还测量了辛基硫酸钠(C8SO4Na)和十六烷基硫酸钠(C16SO4Na)在十六烷-水界面上的吸附自由能,这有助于我们更加深入地理解阴阳离子表面活性剂在界面上的吸附行为。第三部分通过SHG方法研究了阴离子表面活性剂(CnSO4Na)和阳离子表面活性剂(CnTAB)等摩尔混合在十六烷-水界面上的吸附过程。考察了总链长增加或者保持不变时,阴阳离子表面活性剂混合在十六烷-水界面吸附自由能变化。研究发现随着总链长的增加,阴阳离子表面活性剂混合时的吸附自由能数值变得更负。总链长相同时,不同阴阳离子表面活性剂混合时的吸附自由能也不相同。实验结果表明阴阳离子表面活性剂混合时的总链长和链长之间的匹配度都会影响它们在界面的吸附自由能。本部分研究有助于加深对阴阳离子表面活性剂在油-水界面吸附行为的理解。综上所述,本论文主要通过SHG方法研究了阳离子表面活性剂、阴离子表面活性剂、阴阳离子表面活性剂混合在十六烷-水界面上的吸附动力学过程。从链长对表面活性剂吸附影响的角度,该工作更加深入地考察了表面活性剂从体相吸附到界面的过程,对长链离子型表面活性剂吸附到界面上的主要驱动力及吸附行为有了更深入的认识。

其他摘要

The properties of the adsorbed molecules, nature of the surface and composition of the solvent have a great influence on the adsorption rate, structure and interfacial density of adsorbate molecules. This thesis mainly studies the adsorption of ionic surfactants with various chain lengths at the hexadecane-water interface by sensitive and interface selective Second Harmonic Generation (SHG) technique. In the first part, the adsorption of various chain lengths cationic surfactants C3TAB, C6TAB, C8TAB and C12TAB at the hexadecane-water interface was systematically studied by SHG. The adsorption free energies of surfactants were obtained by fitting with Langmuir model. The adsorption free energy of per methylene group was also obtained by linear fitting adsorption free energy versus the carbon chain length. The adsorption free energy of per methylene group of cationic surfactants at the hexadecane-water interface is lower than that obtained by other researchers at the air-water interface. This indicates the chain-chain interaction at the hexadecane-water interface is lower than that at the air-water interface. This finding provided another explaination for the driving force of the surfactant adsorbing at interface from bulk phase. We also studied the adsorption of various chain length fatty amines CnNH2 (n=10, 12, 14, 16, 18) at the hexadecane-water interface. The adsorption free energies do not change regularly with carbon chain length, this may be due to the dissociation and hydrogen bond structure of fatty amines at the interface. In the second part, the adsorption of various chain lengths anionic surfactants C9COOH, C11COOH, C13COOH, C15COOH and C17COOH at the hexadecane-water interface was systematically studied by SHG. The adsorption free energies of surfactants became more negative with the increasing carbon chain length. We also found the adsorption free energy of per methylene group for oil-soluble anionic carboxylic acids was close to that for water-soluble cationic quaternary ammonium salts, this observation revealed that the chain-chain interaction rather than the lyophobicity of the solute with respect to the solvent was the main contributor to the adsorption free energy. And the obtained adsorption free energy of head groups provided a method for estimating the solvation energy of some head groups in surfactants. We also studied the adsorption of the sodium octyl sulfate (C8SO4Na) and sodium hexadecyl sulphate (C16SO4Na) at the interface, the obtained adsorption free energies would be helpful to the better understanding the adsorption of anionic and cationic surfactants at the interfaces. In the third part, the adsorption of equal molar anionic surfactant (CnSO4Na) and cationic surfactant (CnTAB) at the hexadecane-water interface was studied by SHG. With the total carbon chain length increasing or keeping constant, the adsorption free energies were obtained. The adsorption free energies became more negative with the increasing carbon chain length. The adsorption free energies were different for the same total carbon chain length. The results indicated both the total carbon chain length and chain length compatibility had influence on the adsorption of anionic and cationic surfactants at the interface. The results would help us understand the adsorption of anionic and cationic surfactants at the interfaces deeply. In conclusion, this thesis studies the adsorption of the anionic surfactant, cationic surfactant and mixture of anionic surfactant and cationic surfactant at the hexadecane-water interface mainly by SHG technique. We have a deeper understanding of adsorption of the surfactants at interfaces through the obtained adsorption free energy of various chain length surfactant. This work reveals the major driving force for the long chain surfactants from the bulk phase to the interface is the chain-chain interaction.

页数88
文献类型学位论文
条目标识符http://ir.xjipc.cas.cn/handle/365002/5427
专题环境科学与技术研究室
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梁远振. 离子型表面活性剂的界面吸附动力学与分子链长关系的二次谐波研究[D]. 北京. 中国科学院大学,2018.
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