反相微乳液的电导研究及其在氧化铝纳米颗粒制备上的应用

【作者】 黄淼淼；

【导师】 孙洪巍；

【作者基本信息】 郑州大学 ， 凝聚态物理， 2007， 硕士

【摘要】 本文利用CTAB／正丁醇／环己烷／Al（NO₃）₃（NH₃·H₂O）溶液四组分反相微乳液中的纳米水核为模板，采用微乳液法成功制备了具有纳米级粒径，颗粒大小分布均匀，分散性好的球形Al₂O₃颗粒。本文包括反相微乳液的选择和Al₂O₃纳米颗粒的制备两部分内容，采用目视和电导测量相结合的研究手段，对CTAB／正丁醇／环己烷／水四组分体系的微观结构进行了研究，探讨了表面活性剂CTAB、助表面活性剂正己醇的用量及分散相类型的改变对该体系处于W／O结构时水相的最大增溶量及体系稳定性的影响，找到了适合制备Al₂O₃纳米粒子的反相微乳液的最佳配比。然后以此配比下的反相微乳液为模板，通过改变不同的反应条件，成功合成了不同粒径的Al₂O₃纳米颗粒。采用SEM、TG-DSC和XRD等测试手段对所得粉体进行了表征。所得结论主要有以下几点：（1）通过CTAB对CTAB／正丁醇／环己烷／水微乳液在油包水结构时对增溶水量的考察，发现表面活性剂CTAB的含量对该反相微乳液的稳定性有明显的影响。表面活性刘CTAB在油相环己烷中的浓度小于0.6mol／L时，随着CTAB浓度的增大，不仅油相中反胶束的数量增多，而且单个胶束的聚集数增加，因而反相微乳液的最大增溶水量增大，稳定性增强。当表面活性剂CTAB的浓度大于0.6mol／L时，由于CTAB所形成的胶束在油相中的浓度不再变化，因此反相微乳液的最大增溶水量基本不再变化，再者，由于过多的CTAB溶解在油相中，CTAB的碳氢链相互交织缠绕造成微乳液的稳定性下降。（2）在CTAB／正丁醇／环己烷／水微乳液中，助表面活性剂正丁醇的含量对界面膜强度的影响非常大。实验发现，正丁醇在油相环己烷的浓度为3.5mol／L时，该微乳体系的界面膜强度较大，稳定性较好。但正丁醇含量的大小对该反相微乳液的最大增溶水量的影响不大。正丁醇浓度值大于或小于3.5mol／L时，该微乳体系的稳定性都将降低。（3）对于CTAB／正丁醇／环己烷／水反相微乳液，将水相替换为Al（NO₃）₃溶液和NH₃·H₂O溶液，该体系的最大增溶量将随着电解质浓度的增大而减小，而且水量小于水相为去离子水的含水量。这是由于离子的加入压缩了表面活性剂极性头基的扩散双电层，微乳体系的稳定性下降，使体系对水溶液的增溶能力降低。（4）微乳液在合适的配比下，随着增溶水量的增加，CTAB／正丁醇／环己烷／水微乳液连续经过三种微结构的变化，即油包水（W／O）、油水双连续（BC）及水包油（O／W）三种类型，并且当该微乳液处于油包水结构时，其电导率呈现典型的渗滤特征。（5）根据微乳体系的电导率曲线来判定微乳液的结构是可行的，选择制备Al₂O₃纳米颗粒的反相微乳液的最佳配比如下：油相环己烷的体积固定不变，表面活性剂CTAB的浓度为0.6mol／L，助表面活性剂正丁醇浓度为3.5mol／L。（6）在其他反应条件相同的情况下，Al₂O₃粒子粒径可通过调节微乳液组成中的水量来控制。由于反相微乳液的水核大小与ω值密切相关，而水核的大小限制了纳米颗粒的生长，根据ω=[water]／[surfant]，因此粒子粒径可通过调节组成中的水量来控制。实验结果表明，ω₁∶ω₂∶ω₃=1∶2∶3时，Al₂O₃颗粒D（ω1）、D（ω2）（D₂）、D_ω3的直径分别为30nm、40nm和80nm，颗粒直径随ω的增大而明显增大。但是当水量过多时，表面活性剂不能实现对水核的良好包覆，界面膜的强度变差，水核容易变形、破裂，对粒径的控制能力削弱，导致获得的纳米粒子的不仅粒径增大而且分散性较差。（7）在其他反应条件相同的情况下，Al₂O₃颗粒直径随微乳液中水核中增溶的反应物浓度的增加而增大。实验结果表明，Al（NO₃）₃溶液的浓度分别为0.1mol／L、0.5mol／L和1mol／L时，所对应的Al₂O₃颗粒的粒径分别为25nm、40nm和50nm。但是当反应物的浓度过大时，造成微乳液的稳定性下降，导致生成的纳米颗粒的分散性降低。（8）通过SEM、TG-DSC和XRD对本实验中制备的Al₂O₃纳米颗粒进行分析可知，用微乳液法制备的Al₂O₃前驱体在1150℃时就完全转化为α-Al₂O₃，比传统的制备方法所需的1200℃以上的温度要低。所得粉体粒度分布均匀，分散性好。更多还原

【Abstract】 Spherical alumina nanoparticles with homogeneous size distribution and good dispersity are obtained successfully by double-microemulsion.Water nucleus in the four-component system of Cetyltrimethyl Ammonium Bromide （CTAB） /n-butanol/cyclohexane/ aluminum nitrate （ammonia liquor） microemulsion is used as form board, where aluminum nitrate and ammonia liquor react.This article contains two parts: the choice of reverse microemulsion and the preparation of alumina nanoparticles.The four-component system of CTAB/n-butanol/cyclohexane/water microemulsion is studied by measuring the electrical conductivity and watching. Some factors are changed, such as the content of surfactant CTAB, cosurfactant n-butanol and the type of disperse phase. The effect of these factors on the maximum volume of solubilizing water and stability of the water-in-oil system is discussed. The reverse microemulsion with proper proportion is found by experiment, and then alumina nanoparticles with different particle size are prepared by changing reactive conditions in this reverse microemulsion.The powders are characterized by SEM, TG-DSC and XRD measurements. The main conclusions in this article are as follows:（1） The content of surfactant CTAB has an obvious effect on the stability of the reverse microemulsion through the comparison of the maximum volume of solubilizing water in different water-in-oil microemulsion systems. When the concentration of surfactant CTAB is less than 0.6mol/L in oil phase of cyclohexane, not only the numbers of reverse micelles but also aggregation of each micelle all increase along with the increase of the concentration of surfactant CTAB, so the maximum volume of solubilizing water is enlarged and stability of the water-in-oil microemulsion system is strengthened. When the concentration of surfactant CTAB is more than 0.6mol/L,because the concentration of surfactant CTAB is not change any more, the maximum volume of solubilizing water in water-in-oil microemulsion systems is not variable. Otherwise, over many carbon hydrogen links of CTAB interwind, this brings about the falling of the stability of the reverse microemulsion.（2） In the CTAB/n-butanol/cyclohexane/water microemulsion system, the content of cosurfactant n-butanol has a great effect on the interfacial film of the reverse microemulsion. When the concentration of cosurfactant n-butanol is 3.5mol/L in oil phase of cyclohexane and the interfacial film is more intensive, so the microemulsion is more stable. But the concentration of cosurfactant n-butanol has little effect on the maximum volume of solubilizing water. The content of cosurfactant n-butanol is more than or less than 3.5mol/L, the stability of reverse microemulsion will fall.（3） When using aluminum nitrate （ammonia liquor） instead of water phase, we found the maximum volume of solubilizing solution will fall along with the increase of the concentration of electrolyte solution in the CTAB/n-butanol/cyclohexane/water microemulsion system and the volume of solution is less than the volume of de-ionized water. It is because ions compress double electric layer of polar group of surfactant, the stability of reverse microemulsion will fall.（4） The CTAB/n-butanol/cyclohexane/water reverse microemulsion with proper proportion goes through three microstructures successively, when the volume of solubilizing de-ionized water increase. They are water droplets in oil, bicontinuous structure and oil droplets in water. The electrical conductivity presents typical percolation filtration phenomenon, when the microstructure of microemulsion is water droplets in oil.（5） It is feasible method that using the variation curves of the electrical conductivity judges the microstructure of microemulsion. Proper proportion of the reverse microemulsion is the concentration of surfactant CTAB is 0.6mol/L and the concentration of cosurfactant n-butanol is 3.5mol/L in oil phase of cyclohexane.（6） In the case of reactive conditions maintain unchanging, the grain size of alumina nanoparticles can be controlled by the adjustment of the volume of water. The diameter of water nucleus in reverse microemulsion is relative toωvalue, and it also restricts the growth of nanoparticles. According toω=[water]/[surfant],the particle size of nanoparticles can be controlled by the adjustment of the volume of water. The result shows that the diameter of alumina D_ω1, D_ω2（D₂） and D_ω3 is 30nm, 40nm and 80nm, whenω₁:ω₂:ω3=1:2:3. The diameter of alumina nanoparticles increase along withωvalue. The strength of interfacial film go worse, water nucleus go distorted and broken, so the ability of controlling the size of nanoparticles will weaken, when the volume of water is too much. These factors results in the growth of the particle size and the worse of dispersity.（7） In the case of reactive conditions maintain unchanging, the grain size of alumina nanoparticles will grow along with the increase of concentration of reactant. The results show that the particle size of alumina nanoparticles is 25nm, 40nm and 50nm, when the concentration of aluminum nitrate solution is 0.1 mol/L, 0.5mol/L and 1 mol/L.But the stability of microemulsion will reduce, when the concentration of reactant is too much. The dispersity of nanoparticles will fall.（8） Alumina nanoparticles are characterized by SEM, TG-DSC and XRD measurements. The precursor of alumina becameα- Al-2O-3 at 1150°C completely by double-microemulsion method. Compared with 1200°C in conventional method, it is lower. The size distribution of the powders is homogeneous and the dispersity is good.更多还原