Yao Kaixin, Sun Lijie, Ding Xiaoxuan, Wang Yuzhao, Liu Tianze, Liu Changyao, Tan Jiajing, Zhao Li, Xu Baocai, Romsted Larry
Department of Applied Chemistry, Beijing Technology and Business University, No. 11 Fucheng Road, Beijing, 100048, People's Republic of China.
Department of Organic Chemistry, College of Chemistry, Beijing University of Chemical Technology, Beijing 100029, P. R. China.
Soft Matter. 2020 Jun 10;16(22):5148-5156. doi: 10.1039/d0sm00665c.
The transitions between surfactant aggregate structures are triggered by changes in chemical or physical stimulations, including addition of additives. Effects of added alcohols on aggregate morphologies correlate strongly with alcohol chain length. The local molarities of alcohol, water, and counterions in the interfacial regions play an important role in controlling the aggregate morphologies. However, direct experimental estimates of changes of interfacial alcohol molarities during alcohol induced micelle-to-vesicle transitions have never been reported. Ellipsoidal-wormlike micelle-vesicle transitions in CTAB/KBr aqueous solutions in the presence of long-chain octanol were characterized by using combined rheological, dynamic light scattering (DLS), transmission electron microscopy (TEM) and turbidity measurements. However, the transitions are absent with added butanol. The chemical trapping method (CT) was employed to understand the differences between medium- and long-chain alcohols in determining aggregate morphology. The CT method was used to estimate interfacial water, alcohol, and counterion molarities with increasing stoichiometric alcohol concentrations. With 55 mM alcohol added, the interfacial octanol molarity is 0.9 M, which is three times higher than that for butanol. With added octanol, the ellipsoidal-wormlike micelle-vesicle transition is accompanied by a concurrent sharp increase of interfacial water molarities and a decrease of interfacial counterion molarity, which is not observed with added butanol. The CT data was also employed to estimate the changes of Israelachvili's packing parameter with increasing added alcohol concentration. Our result provides critical molecular level information for understanding the morphological transitions of CTAB/additives.
表面活性剂聚集体结构之间的转变是由化学或物理刺激的变化引发的，包括添加剂的加入。添加的醇类对聚集体形态的影响与醇链长度密切相关。界面区域中醇、水和抗衡离子的局部摩尔浓度在控制聚集体形态方面起着重要作用。然而，从未有过关于醇诱导胶束到囊泡转变过程中界面醇摩尔浓度变化的直接实验估计。通过结合流变学、动态光散射（DLS）、透射电子显微镜（TEM）和浊度测量，对在长链正辛醇存在下CTAB/KBr水溶液中的椭球形蠕虫状胶束 - 囊泡转变进行了表征。然而，添加丁醇时不存在这种转变。采用化学捕获法（CT）来理解中链和长链醇在确定聚集体形态方面的差异。CT方法用于估计随着化学计量醇浓度增加时界面水、醇和抗衡离子的摩尔浓度。添加55 mM醇时，界面正辛醇摩尔浓度为0.9 M，是丁醇的三倍。添加正辛醇时，椭球形蠕虫状胶束 - 囊泡转变伴随着界面水摩尔浓度的同时急剧增加和界面抗衡离子摩尔浓度的降低，而添加丁醇时未观察到这种情况。CT数据还用于估计随着添加醇浓度增加时以色列阿哈维利堆积参数的变化。我们的结果为理解CTAB/添加剂的形态转变提供了关键的分子水平信息。
