【作者】 沈玉文；

【导师】 郝京诚；

【作者基本信息】 山东大学 ， 胶体与界面化学， 2010， 博士

【摘要】 当表面活性剂的浓度高于其临界胶束浓度(critical micelle concentration, cmc)时,可以在溶液中自发形成各种有序聚集体,如球状胶束、棒状胶束、蠕虫状胶束、囊泡、层状液晶等。这些有序结构的形成和性质决定了表面活性剂在工业中的诸多功用,如作为药物载体、仿生物膜、微反应器等。当溶液中含有两种或两种以上表面活性剂时,会产生协同作用,从而具有很多独特性质：如低临界聚集浓度、低界面张力、形成的聚集体种类丰富等。这些性质使混合表面活性剂体系具有了更高的工业应用价值。本论文系统研究了离子强度、温度、溶剂极性、剪切力等外界因素对混合表面活性剂体系聚集行为的影响,用基本的物理化学知识阐述了产生这些影响的本质原因,希望能达到通过调控外界条件来控制表面活性剂聚集体形貌的最终目的。具体研究内容如下：第一章中简要介绍了与本论文密切相关的基本知识、国内外近几年的研究动态及论文选题的科学意义。在第二章至第四章中,分别研究了离子强度、温度和溶剂极性对碳氢阴／阳离子表面活性剂混合体系的影响：第二章中选取阳离子表面活性剂十四烷基三甲基氢氧化铵(TTAOH)和阴离子表面活性剂月桂酸(LA)按摩尔比1：1复配形成的无盐的阴／阳离子表面活性剂TTAL囊泡体系,研究了小分子无机盐NaBr对其聚集行为的影响,着重探讨了极高盐度下TTAL聚集行为的变化情况。研究主要围绕小分子无机盐对表面电荷的屏蔽作用展开,囊泡双分子层上的表面电荷间的斥力是溶液中聚集体稳定分散的来源,加入的少量NaBr电离出的Na+和Br-会屏蔽表面电荷间的斥力,导致囊泡发生聚集。当阴／阳离子表面活性剂与加入NaBr的浓度接近1：1时,由于表面活性剂密度比水小,聚集后的囊泡形成白色“沉淀”浮在溶液上层。当NaBr的浓度超过TTAL的浓度时,体系逐渐变为具有双折射纹理的均相,盐度越高溶液越澄清,直至达到NaBr的饱和溶解度为止。温度是影响聚集体存在的重要因素,因此,第三章中研究了温度对阴／阳离子表面活性剂混合体系的影响。选取的是TTAL/NaBr/H2O形成的“沉淀”／胶束两相体系,研究其在不同温度下的聚集行为变化。当温度升高到表面活性剂的链熔化温度以上,处在上层“沉淀”相中密堆积的多层囊泡结构转变为三维网络状双层结构并分布在整个体相溶液中,形成了具有双折射纹理的均相,并且体系的结构转化温度随含盐量的增加而升高。相转变的原因主要是由于温度的升高增加了囊泡双分子层间的Helfrich自由能,导致层与层间斥力增加,原来密堆积的双分子层肿胀后重新闭合形成三维网络状的双分子层结构造成的。除盐度和温度外,溶剂的极性也是影响表面活性剂聚集行为的重要因素。在第四章中用甘油来逐步替代“沉淀”／胶束两相体系中的水溶剂来研究溶剂极性对此含盐阴／阳离子表面活性剂混合体系的影响。两相体系是由阳离子表面活性剂十四烷基三甲基溴化铵(TTABr)与阴离子表面活性剂月桂酸钠(SL)按摩尔比1：1复配形成的TTAL和相同物质量的NaBr组成。当甘油占总溶剂的浓度高于40%时,会提高TTAL在混合溶剂中的cmc,降低在体相溶液中形成聚集体的聚集数,导致体系发生了由Lα单相到Lα／L1两相最终到L1单相的一系列相变突跃。而当甘油浓度低于40%时,体系中分布在上相的密堆积的囊泡双层发生肿胀,变成了均一的Lα单相,形成了尺寸比较小的囊泡。这是因为溶剂极性的改变会导致折射率发生变化,当溶剂的折射率与溶质折射率相匹配时,体系的Van der Waals引力最小这时斥力占主导,引起了双分子层的肿胀。剪切力是表面活性剂混合体系中经常引入的外加力,也是需要考虑的重要外界因素。由于阴／阳离子表面活性剂体系中两类分子间的静电作用力很强,剪切力对其作用相对较弱。因此我们在第五章中选取了非离子表面活性剂带有五个乙氧基的十三烷基醇(IT5)与阴离子表面活性剂十二烷基硫酸钠(SDS)形成的粘弹性较高的多层囊泡体系,研究不同剪切力对其结构的影响。将此溶液置于流变仪的转筒-转子夹具中,施以不同速率的剪切力,溶液中的多层囊泡的外层会被剪切力脱去,形成新的单层囊泡,数量密度的增加提高了整个体系的粘弹性。当溶液被置于乳化器中被施以不同的压力来引入剪切时,体系的粘弹性完全丧失,Cryo-TEM照片显示体系中形成了直径较小的单层囊泡,而囊泡之间的间距相对增大,因此体系不再会因为囊泡和囊泡之间的密集排列相互挤压而产生粘弹性。通过进一步的拟合发现对乳化器施加的压力和形成囊泡的直径间呈线性关系。因此,可以通过调节乳化器的压力来控制囊泡的大小。在论文的最后一章中研究了外加表面电荷和剪切力对两性离子表面活性剂十四烷基二甲基氧化胺C(14)DMAO和非离子表面活性剂带有三个乙氧基的十三烷基醇(IT3)混合体系形成的海绵(L3)相的影响。在不引入剪切力的前提下,向L3相中加入甲酸甲酯,其水解产物甲酸将可以C14DMAO质子化,这时原本自发曲率为零的L3相中的双分子层表面带有了正电荷,改变了双分子层的曲率,L3相转变为平面层状结构。对此层状结构施加一定的剪切力时,层状相才能闭合形成囊泡。同时证明了囊泡并不是热力学稳定体系。更多还原

【Abstract】 It is well known that surfactants can self-assemble into various aggregates such as spherical micelles, rod-like micelles, worm-like micelles, vesicles, lamellar liquid crystallines and so on, when the concentration is above the critical micelle concentration (cmc). The wide-ranging applications of surfactant aggregates as drug delivery, selective biomembranes and microreactors depend on the structure and properties of aggregates. The synergistic effect of mixed surfactant systems makes them with fascinating properties, such as low critic aggregates concentration, low surface tension, colorful morphologies of colloid particles. Besides the properties of surfactants, total concentration, some external conditions such as ionic strength, temperature, solvent and shear force also can affect the phase behavior of surfactant aggregates.In this thesis we investigate the phase transition of surfactant aggregates influenced by external conditions in order to control the morphologies of colloid particles. The outline and contents of this doctoral thesis are as follows:ChapterⅠis a brief introduction of basic knowledge of colloid and interface science and the research background and recent improvement of cationic and anionic surfactant mixed system. The object and scientific significance of this thesis are also discussed at the end of this chapter.In chapterⅡ-Ⅳthe phase behavior of cat-anionic surfactant system influenced by ionic strength, temperature and solvent was investigated in more detail. In chapterⅡthe phase transition of salt-free catanionic (mixtures of cationic and anionic surfactants) tetradecyltrimethylammonium laurate (TTAL) system affected by salt (NaBr) was described. With increasing concentration of NaBr, the salt-free catanionic birefringent Lα-phase formed by cationic tetradecyltrimethylammonium hydroxide (TTAOH) and lauric acid at equlimolar mixtures was transferred into a two-phase precipitate/L1-phase and finally a birefringent La-phase again at much higher salt concentration. The interlamellar distance of the precipitated vesicles is much smaller than that of salt-free or high-salinity catanionic vesicles. It is therefore supposed that the phase transition is aroused from the reduction of the repulsive between the bilayers by the excess salts and the interlamellar forces between the bilayers become attractive.In ChapterⅢ, the phase behavior of precipitate/L1 two-phase system with different amount of NaBr was investigated at different temperature. These densely packed multilamellar vesicles of two-phase system can be transformed into three-dimemtional network lamellar at high temperature. This phase transition is progressive process and happens at the chain melting temperature of surfactants. We also found that the phase transition temperature (Tm) was influenced by adding different amounts of salt but not by being diluted. This is the first time to observe the phase conversion from catianionic surfactant vesicles to bilayer networks triggered by chain melting, which the phase structural transition should arise from the enhanced membrane elasticity accompanying the catanionic surfactant state fluctuations on chain melting and the solvent-associated interactions including cationic and anionic surfactant electrostatic interaction that favor a change in membrane curvature. The energy of the fluctuation attained by heating surpasses the loss of the edge energy (the hydrocarbon tails of the surfactant bilayers are exposed to water). And then the multilamellar vesicles open up around the chain melting temperature and restructure to three dimensional networks.Besides ionic strength and temperature, the polarity of the solvent also plays an important role in the morphology of surfactant aggregates. In chapter IV we found that the swelling of lamellar phase can be induced by the replacement of solvent in tetradecyltrimethylammonium bromide (TTABr) and sodium laurate (SL) aqueous solution which contains cream floating precipitates on the upper phase and L1-phase (micelles) at the lower phase. Phase transition, from cream floating precipitates to swelling birefringent vesicle phase, La/L1 two phase, and finally to micelle phase, can be induced by adding glycerin as solvent in aqueous solution. At first, densely packed multilamellar vesicles of cream floating precipitates on the upper phase swelled to the whole phase with increasing the content of glycerin. The replacement of solvent lowers the turbidity of the dispersion and swells the interlamellar distance between the bilayers, which is explained by matching of refractive index of the solvent to the refractive index of the bilayers of the surfactant mixtures. With more glycerin, the swelling La phase transfered La/L1 two-phase, and finally L1 phase (micelles). This phase transition can also be explained because of increasing cmc of cationic and anionic (catanionic) surfactant mixture (TTABr and SL) at high glycerin concentration. The phase transition induced by addition of sorbitol can also be studied and compared to the case of adding glycerin. These results may direct toward acquiring an understanding of the phase transition mechanism of catanionic surfactants induced by solvents.Because of the high electrostatic interaction of cat-anionic surfactant system, shear force almost can not influence the morphology of cat-anionic surfactant aggregates. So in chapter V we chose viscoelastic multilamellar vesicle phase formed by certain amount of nonionic surfactant, polyethylene glycol ether of tridecyl alcohol with the average number of ethylene oxide of 5 (CH3(CH2)(12)(OCH2CH2)5OH, abbreviated Trideceth-5 or IT5) and anionic surfactant SDS (sodium dodecyl sulfate) in aqueous solution and investigated in different shear field. The bilayers of multilamellar vesicles will be stripped off and become densely packed unilamellar vesicles by shear which increases the viscoelasticity of the system. However, through homogenizer the new-formed unilamellar vesicles become so small that they have relative larger distance between each other. The vesicles will not be crowded any more and can easily pass each other under shear. So the unilamellar vesicles through homogenizer only have very low viscoelasticity and flow birefringence. It takes very long time for the unilamellar vesicles to come back to the original state. So it is a good method to control the size of the vesicles.In the last chapter we studied the influence of surface charges and shear force simultaneously to the nonionic surfactant system. A sponge phase (L3 phase) was observed in the mixed system of nonionic surfactants, polyethylene glycol ether of tridecyl alcohol with the average number of ethylene oxide of 3 (CH3(CH2)(12)(OCH2CH2)3OH, abbreviated Trideceth-3) and tetradecyldimethylamino oxide , abbreviated C(14)DMAO), in aqueous solution. The L3 phase can be transferred to lamellar phase (L(αl) phase) after the bilayer was protonated by the formic acid formed through the hydrolysis of methylformate. The L(αl) phase can be transformed into multilamellar vesicles (L(αv) phase) under shear. The properties of L3 phase were investigated by conductivity and rheology measurements. The phase transition from L3 to vesicles was characterized by rheology measurements,2H NMR spectra, polarized microscope, scanning electron microscope (SEM), and transmission electron microscope (TEM) observations.We hope that the report of the controlled phase transition through protonation and shearing forces in nonionic surfactant mixtures may direct primarily us how to achieve the phase transition in surfactant solution by changing the conditions and secondarily to acquire the applications such as the controlled materials from the phase transition as templates.更多还原