Perfluorooctanoate in Aqueous Urea Solutions: Micelle Formation, Structure, and Microenvironment
Perfluorooctanoate in Aqueous Urea Solutions: Micelle Formation, Structure, and Microenvironment
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DOI：
10.3390/ijms20225761
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发表时间：
2019-11-01
影响因子：
5.6
通讯作者：
Alexandridis, Paschalis
中科院分区：
文献类型：
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作者：
Kancharla, Samhitha;Canales, Emmanuel;Alexandridis, Paschalis
氟化表面活性剂用于广泛的应用中，包括掺入各种添加剂的水性溶剂。预计尿素等有机化合物的存在会影响含氟表面活性剂的自组装，但人们对此知之甚少。研究了尿素对常用含氟表面活性剂全氟辛酸铵（APFO）在水中胶束化的影响，以及对APFO形成胶束的结构和微环境的影响。在APFO水溶液中加入尿素降低了临界胶束化浓度（CMC），增加了反胶束解离。所观察到的每个APFO头基的表面积的增加和胶束表面的堆积密度的降低表明脲以减少头基排斥的方式定位在胶束表面。微极性数据进一步支持这一观点。结果表明，尿素对含氟表面活性剂和烃类表面活性剂在水溶液中胶束化的影响存在显著差异。例如，十二烷基硫酸钠（SDS）的CMC随着尿素的加入而增加，而SDS的每个头基的表面积和堆积密度随着尿素的加入而增加的幅度远低于APFO。这项研究通知氟化表面活性剂的命运和运输在环境中，也涉及尿素或类似的添加剂存在的水介质中的应用。
Fluorinated surfactants are used in a wide range of applications that involve aqueous solvents incorporating various additives. The presence of organic compounds such as urea is expected to affect the self-assembly of fluorinated surfactants, however, very little is known about this. We investigated the effect of urea on the micellization in water of the common fluorinated surfactant ammonium perfluorooctanoate (APFO), and on the structure and microenvironment of the micelles that APFO forms. Addition of urea to aqueous APFO solution decreased the critical micellization concentration (CMC) and increased the counterion dissociation. The observed increase in surface area per APFO headgroup and decrease in packing density at the micelle surface suggest the localization of urea at the micelle surface in a manner that reduces headgroup repulsions. Micropolarity data further support this picture. The results presented here indicate that significant differences exist between urea effects on fluorinated surfactant and on hydrocarbon surfactant micellization in aqueous solution. For example, the CMC of sodium dodecyl sulfate (SDS) increased with urea addition, while the increase in surface area per headgroup and packing density of SDS with urea addition are much lower than those observed for APFO. This study informs fluorinated surfactant fate and transport in the environment, and also applications involving aqueous media in which urea or similar additives are present.