Synthesis and Aggregation Behavior of a Hexameric Quaternary Ammonium Surfactant

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• 作者：Yaxun Fan ; Yanbo Hou ; Junfeng Xiang ; Defeng Yu ; Chunxian Wu ; Maozhang Tian ; Yuchun Han ; Yilin Wang
• 刊名：Langmuir
• 出版年：2011
• 出版时间：September 6, 2011
• 年：2011
• 卷：27
• 期：17
• 页码：10570-10579
• 全文大小：1119K
• 年卷期：v.27,no.17(September 6, 2011)
• ISSN：1520-5827

文摘

A star-shaped hexameric quaternary ammonium surfactant (PAHB), bearing six hydrophobic chains and six charged hydrophilic headgroups connected by an amide-type spacer group, was synthesized. The self-assembly behavior of the surfactant in aqueous solution was studied by surface tension, electrical conductivity, isothermal titration microcalorimetry, dynamic light scattering, cryogenic transmission electron microscopy, and NMR techniques. The results reveal that there are two critical aggregate concentrations during the process of aggregation, namely C₁ and C₂. The aggregate transitions are proved to be caused by the changes of the surfactant configuration through hydrophobic interaction among the hydrocarbon chains. Below C₁, PAHB may present a star-shaped molecular configuration due to intramolecular electrostatic repulsion among the charged headgroups, and large aggregates with network-like structure are observed. Between C₁ and C₂, the hydrophobic interaction among the hydrophobic chains may become stronger to make the hydrophobic chains of the PAHB molecules curve back and pack more closely, and then the network-like aggregates transfer to large spherical aggregates of 100 nm. Beyond C₂, the hydrophobic interaction may become strong enough to cause the PAHB molecular configuration to turn into a pyramid-like shape, resulting in the transition of the spherical large aggregates to spherical micelles of 10 nm. Interestingly, the PAHB displays high emulsification ability to linear fatty alkyls even at very low concentration.