Institute of Colloid and Interface Chemistry, College of Chemistry and Chemical Engineering, Fuzhou University, Fuzhou, Fujian 350108, China.
Soft Matter. 2016 May 7;12(17):4044-51. doi: 10.1039/c6sm00207b. Epub 2016 Mar 29.
An equally-charged mixture of an anionic gemini surfactant, O,O'-bis(sodium 2-tetradecylcarboxylate)-p-azodiphendiol (G14-azo), and a cationic surfactant, cetyltrimethylammonium bromide (CTAB), was dissolved in cyclohexane to form reverse worm-like micelles. Samples with different surfactant concentrations and amounts of added water were studied using rheological measurements. The amount of water, represented as the molar ratio of water to total surfactants W0, was c. 13 (at its minimum) in these equally charged systems of G14-azo (200 mmol L(-1))/CTAB. The low shear viscosity ηL of this system reached 4370 Pa s at W0 = 13 and the dynamic rheological result showed typical surfactant gel behaviour. Under UV-light irradiation, the transparent sample (G14-azo (300 mmol L(-1))/CTAB (600 mmol L(-1))) at W0 = 40 became turbid, during which ηL was rapidly reduced from the original 285 Pa s to 0.3 Pa s, indicating a transition of aggregate morphology from reverse worms into simple reverse micelles. Then the sample was returned to its original homogeneous state with c. 290 Pa s viscosity under visible light irradiation. However, this transition cannot be well achieved at low W0 due to the interior cores being too small. This limit has been attributed to both the Gemini type of surfactant molecule and to the inverted structure of aggregates.
一种阴离子双子表面活性剂 O,O'-双（2-十四烷羧酸钠）-对偶氮二苯酚（G14-偶氮）和阳离子表面活性剂十六烷基三甲基溴化铵（CTAB）的等电荷混合物溶解在环己烷中形成反向蠕虫状胶束。使用流变学测量研究了具有不同表面活性剂浓度和添加水量的样品。水的量表示为水与总表面活性剂的摩尔比 W0，在 G14-偶氮（200 mmol L(-1))/CTAB 的这些等电荷体系中约为 13（最小值）。该体系的低剪切粘度 ηL 在 W0 = 13 时达到 4370 Pa s，动态流变学结果显示出典型的表面活性剂凝胶行为。在紫外光照射下，W0 = 40 时的透明样品（G14-偶氮（300 mmol L(-1))/CTAB（600 mmol L(-1)))）变得浑浊，在此期间 ηL 从原始的 285 Pa s 迅速降低到 0.3 Pa s，表明聚集形态从反向蠕虫转变为简单的反向胶束。然后，在可见光照射下，样品恢复到原始的均匀状态，粘度约为 290 Pa s。然而，由于内部核心太小，在低 W0 下无法很好地实现这种转变。这种限制归因于双子表面活性剂分子的类型和聚集结构的反转。
