Key Laboratory of Colloid and Interface Chemistry, Shandong University, Ministry of Education, Jinan 250100, People's Republic of China.
J Phys Chem B. 2010 Aug 5;114(30):9795-804. doi: 10.1021/jp103916a.
The phase behavior, rheological properties, and structures of two salt-free catanionic surfactant systems, tetradecyltrimethylammonium hydroxide ((TTA)OH)/lauric acid (LA)/H(2)O and cetyltrimethylammonium hydroxide ((CTA)OH)/LA/H(2)O, in the presence of deoxycholic acid (DeCA) were investigated and compared with the results of cholic acid (CA). Small-angle X-ray scattering, deuterium nuclear magnetic resonance, and rheological measurements were employed to monitor the phase structure and transition. The surface tension was used to investigate the surface activities of the bile acid/(TTA)OH and bile acid/(CTA)OH mixtures in dilute solutions. The results show that they have a minimum surface tension in a solution with excess cationic surfactant, and the critical micelle concentration decreases with an increase of the cationic surfactant chain length and hydrophobicity of the bile acids. At equimolar mixtures of DeCA and cationic surfactants, or DeCA being in excess, phase separation occurs with a large diameter of droplets in the upper phase and a small volume of viscous liquid in the bottom phase. Compared with CA systems, in the salt-free catanionic surfactant systems containing DeCA, phase transition from the birefringent L(alpha) phase to the L(1) phase occurs at a high molar fraction of DeCA, and the viscosity is higher at the same molar fraction of bile acid, indicating the significant influence of the molecule structures of bile acids despite only one hydroxyl group difference. Shear thickening is observed in the L(alpha) region, and a gradual evolvement of aggregates is predicted. Longer chain cationic surfactant can also increase the shear viscosity, which could be ascribed to the increase of the critical packing parameter, but with less influence on the phase transition.
两种无盐双离子表面活性剂体系十四烷基三甲基氢氧化铵（(TTA)OH）/月桂酸（LA）/H2O 和十六烷基三甲基氢氧化铵（(CTA)OH）/LA/H2O 中存在脱氧胆酸（DeCA）时的相行为、流变性能和结构进行了研究，并与胆酸（CA）的结果进行了比较。小角 X 射线散射、氘核磁共振和流变测量用于监测相结构和转变。表面张力用于研究胆汁酸/(TTA)OH 和胆汁酸/(CTA)OH 混合物在稀溶液中的表面活性。结果表明，它们在阳离子表面活性剂过量的溶液中具有最低的表面张力，并且临界胶束浓度随着阳离子表面活性剂链长和胆汁酸疏水性的增加而降低。在等摩尔比的 DeCA 和阳离子表面活性剂混合，或 DeCA 过量时，会发生相分离，在上相中有大直径的液滴，在下相中有小体积的粘性液体。与 CA 体系相比，在含有 DeCA 的无盐双离子表面活性剂体系中，从双折射 L(alpha)相到 L(1)相的相转变发生在高摩尔分数的 DeCA 处，并且在相同的胆汁酸摩尔分数处具有较高的粘度，表明尽管只有一个羟基的差异，胆汁酸的分子结构有显著的影响。在 L(alpha)区观察到剪切增稠现象，并且预测了聚集物的逐渐演变。长链阳离子表面活性剂也可以增加剪切粘度，这可以归因于临界堆积参数的增加，但对相转变的影响较小。
