Abstract Wormlike micelles in mixed surfactant mixture containing an amino acid-derived anionic surfactant, sodium lauroyl sarcosinate (SLSar), and a zwitterionic surfactant, cocoamidopropyl hydroxysultaine (CAHS) were investigated. The total surfactant concentration was maintained at 15% wt/v, while the ratio of SLSar and CAHS was varied and the pH was lowered from 7.5 to 4.5. Steady-shear rheology, potentiometric titration, cross-polarized microscopy, zeta potential and cryo-TEM were used to obtain zero-shear viscosity and analyze the structure-rheology relationship. As pH dropped, viscosity increased to a maximum followed by a viscosity decrease in four out of five tested systems. The synergistic effect was strongest in the SLSar 6 %:CAHS 9 % composition or an equivalent molar ratio of 1:1 between the two surfactants, for which the viscosity maximum was 9.6 Pa.s at pH 4.8. The viscosity peak of each system occurred in the pH range 4.8–5.0, close to the system’s experimental pKa. The intermolecular forces between the SLSar acid form, SLSar anionic form and CAHS reduced the charge repulsion and contributed to the thickening behavior of these systems.

中文翻译：

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氨基酸衍生的表面活性剂组合物的增稠机制

摘要 研究了含有氨基酸衍生的阴离子表面活性剂月桂酰肌氨酸钠 (SLsar) 和两性离子表面活性剂椰油酰胺丙基羟基磺基甜菜碱 (CAHS) 的混合表面活性剂混合物中的蠕虫状胶束。表面活性剂的总浓度保持在 15% wt/v，而 SLSar 和 CAHS 的比例变化，pH 从 7.5 降低到 4.5。使用稳态剪切流变学、电位滴定、交叉偏振显微镜、zeta 电位和低温-TEM 来获得零剪切粘度并分析结构-流变学关系。随着 pH 值下降，粘度增加到最大值，然后在五个测试系统中的四个系统中粘度降低。在 SLSar 6%:CAHS 9% 组合物或两种表面活性剂之间 1:1 的等效摩尔比中，协同效应最强，其最大粘度为 9.6 Pa.s，pH 值为 4.8。每个系统的粘度峰值出现在 4.8-5.0 的 pH 范围内，接近系统的实验 pKa。SLSar 酸形式、SLSa 阴离子形式和 CAHS 之间的分子间作用力降低了电荷排斥并有助于这些系统的增稠行为。