Anionic–cationic surfactant mixtures are known to exhibit synergistic effects (e.g., low critical micelle concentration, ultralow interfacial tension, middle phase microemulsion formulation, and increased solubilization and adsolubilization). However, the anionic–cationic surfactant mixtures are also prone to form other unique phases such as precipitates, gels, and coacervates in place of middle-phase microemulsions. Research summarized in this article demonstrates that asymmetric anionic–cationic surfactant mixtures have been shown to promote middle-phase microemulsions instead of these other phases, albeit with a slight decrease in synergism when using these asymmetric mixtures. The use of anionic–cationic surfactant mixtures also is shown to enhance or decrease surfactant adsorption depending on anionic–cationic surfactant ratios. Middle-phase microemulsion formation is demonstrated using anionic-rich or cationic-rich alcohol-free microemulsions by anionic–cationic ratio scans while also reducing or eliminating electrolyte requirement. Solubilization and adsolubilization are shown to increase for mixed anionic–cationic surfactant systems, especially for hydrophobic solutes. Thus, by exploiting these synergisms while avoiding phase separation, properly designed anionic–cationic surfactant mixtures can be advantageous for a wide range of applications.

中文翻译：

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阴离子和阳离子表面活性剂协同作用：最大限度地减少沉淀、微乳液的形成以及增强的增溶和表面改性

已知阴离子-阳离子表面活性剂混合物表现出协同效应（例如.、低临界胶束浓度、超低界面张力、中相微乳液配方，并增加增溶和吸附作用）。然而，阴离子-阳离子表面活性剂混合物也容易形成其他独特的相，如沉淀、凝胶和凝聚层，以代替中间相微乳液。本文中总结的研究表明，不对称阴离子-阳离子表面活性剂混合物已被证明可以促进中间相微乳液而不是这些其他相，尽管在使用这些不对称混合物时协同作用略有下降。阴离子-阳离子表面活性剂混合物的使用也显示出根据阴离子-阳离子表面活性剂的比例增强或减少表面活性​​剂吸附。使用富含阴离子或富含阳离子的无醇微乳液通过阴离子 - 阳离子比率扫描证明了中间相微乳液的形成，同时还减少或消除了电解质需求。对于混合阴离子-阳离子表面活性剂体系，特别是疏水性溶质，增溶和吸附作用会增加。因此，通过利用这些协同作用同时避免相分离，适当设计的阴离子-阳离子表面活性剂混合物有利于广泛的应用。