Concentration dependent pathways in spontaneous self-assembly of unilamellar vesicles
Concentration dependent pathways in spontaneous self-assembly of unilamellar vesicles
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DOI：
10.1039/c1sm05354j
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发表时间：
2011-01-01
期刊：
影响因子：
3.4
通讯作者：
Gradzielski, Michael
中科院分区：
文献类型：
--
作者：
Gummel, Jeremie;Sztucki, Michael;Gradzielski, Michael
我们报告了在阴离子和两性离子表面活性剂溶液的稀释溶液混合后形成单层囊泡的结构动力学。采用止流装置快速混合表面活性剂溶液，引发了自发自组装，并利用时间分辨小角x射线散射探测了瞬态中间结构。最初的表面活性剂溶液由阴离子全氟辛酸锂和两性离子十四烷基二甲胺氧化物组成，其中混合物在很宽的浓度和混合比例范围内形成单层囊泡。我们发现，在较高的浓度下会形成圆盘状的瞬态中间结构，而在较低的浓度下会形成更细长的形状，如圆柱形和环状胶束。这些差异归因于当初始浓度远低于阴离子表面活性剂的临界胶束浓度时，单体加成机制主导了自组装过程，而在较高浓度下，该过程由圆盘状混合胶束融合控制。这意味着，囊泡形成的途径是由更容易溶解的组分接近临界胶束浓度决定的。
We report on the structural dynamics underlying the formation of unilamellar vesicles upon mixing dilute solutions of anionic and zwitterionic surfactant solutions. The spontaneous self-assembly was initiated by rapid mixing of the surfactant solutions using a stopped-flow device and the transient intermediate structures were probed by time-resolved small-angle X-ray scattering. The initial surfactant solutions comprised of anionic lithium perfluorooctanoate and zwitterionic tetradecyldimethylamine oxide, where the mixtures form unilamellar vesicles over a wide range of concentrations and mixing ratios. We found that disk-like transient intermediate structures are formed at higher concentrations while more elongated forms such as cylinder-like and torus-like micelles are involved at lower concentrations. These differences are attributed to monomer addition mechanism dominating the self-assembly process when the initial concentration is well below the critical micellar concentration of the anionic surfactant, while at higher concentrations the process is governed by fusion of disk-like mixed micelles. This means that the pathway of vesicle formation is determined by the proximity to the critical micellar concentration of the more soluble component.