Michina Youlia, Carriere David, Mariet Clarisse, Moskura Melanie, Berthault Patrick, Belloni Luc, Zemb Thomas
CEA, IRAMIS, SCM, LIONS (Laboratoire Interdisciplinaire sur l'Organisation Nanométrique et Supramoléculaire), F-91191 Gif-sur-Yvette, France
Langmuir. 2009 Jan 20;25(2):698-706. doi: 10.1021/la8018293.
We have studied the dialysis of surfactant mixtures of two oppositely charged surfactants (catanionic mixture) by combining HPLC, neutron activation, confocal microscopy, and NMR. In mixtures of n-alkyl trimethylammonium halides and n-fatty acids, we have demonstrated the existence of a specific ratio between both surfactant contents (anionic/cationic almost equal to 2:1) that determines the morphology, the elimination of ions, and the elimination of the soluble cationic surfactant upon dialysis. In mixtures prepared with lower anionic surfactant contents, ill-defined aggregates are formed, and dialysis quickly eliminates the ion pairs (H+X-) formed upon surfactant association and also the cationic surfactant until a limiting 2:1 ratio is reached. By contrast, mixtures prepared above the anionic/cationic 2:1 ratio form micrometer-sized vesicles resistant to dialysis. These closed aggregates retain a significant number of ions (30%) over 1000 hours, and dialysis is unable to eliminate the soluble surfactant. The interactions between surfactants have been estimated by measuring the partitioning of the CTA molecules between the catanionic bilayer, the bulk solution, and mixed micelles when they exist. The mean extraction free energy per CTA in the membrane has been found to increase by 1 kBT to 2 kBT as the soluble surfactant is depleted from the bilayer, which is enough to stop the dialysis. The vesicles produced above the anionic/cationic 2:1 ratio are formed by frozen bilayers and are resistant to extensive dialysis and therefore show an interesting potential for encapsulation as far as durability is concerned.
我们通过结合高效液相色谱法（HPLC）、中子活化分析、共聚焦显微镜和核磁共振（NMR）技术，研究了两种带相反电荷表面活性剂的混合物（阴-阳离子混合物）的透析过程。在正烷基三甲基卤化铵和正脂肪酸的混合物中，我们证明了两种表面活性剂含量之间存在特定比例（阴离子/阳离子几乎等于2:1），该比例决定了透析过程中的形态、离子消除以及可溶性阳离子表面活性剂的消除。在制备的阴离子表面活性剂含量较低的混合物中，会形成不明确的聚集体，透析会迅速消除表面活性剂缔合时形成的离子对（H⁺X⁻）以及阳离子表面活性剂，直至达到极限的2:1比例。相比之下，在阴离子/阳离子比例高于2:1的混合物中会形成抗透析的微米级囊泡。这些封闭的聚集体在1000小时内保留了大量离子（30%），透析无法消除可溶性表面活性剂。通过测量CTA分子在阴-阳离子双层、本体溶液和混合胶束（如果存在）之间的分配情况，估算了表面活性剂之间的相互作用。当双层中可溶性表面活性剂耗尽时，发现膜中每个CTA的平均萃取自由能增加了1 kBT至2 kBT，这足以阻止透析。阴离子/阳离子比例高于2:1时产生的囊泡由冻结的双层形成，抗长时间透析，因此就耐久性而言，在封装方面显示出有趣的潜力。
