School of Chemistry, Monash University , Clayton, Victoria 3800, Australia.
Australian Centre for Neutron Scattering, ANSTO, Lucas Heights, New South Wales 2234, Australia.
Langmuir. 2018 Jan 23;34(3):970-977. doi: 10.1021/acs.langmuir.7b02830. Epub 2017 Oct 23.
Long-chain amidopropyl betaines are known for their ability to self-assemble into viscoelastic wormlike micellar structures. Here, we explore the effect of tailgroup molecular architecture on this process, comparing five molecules, each with C18 chains but different levels of unsaturation and branching. The surfactants are synthesized from stearic, oleic, linoleic, linolenic, and isostearic acids. The self-assembly of these molecules in aqueous solutions is explored using small- and ultra-small-angle neutron scattering (SANS and USANS). It is seen that optimum wormlike micelle formation is achieved for the oleic-chained surfactant, and the alignment of self-assembled structures is further explored using rheo-SANS. The more highly unsaturated molecules form rodlike micelles, whereas the stearic-tailed molecule shows a pronounced Krafft point and the isostearic-chained surfactant is entirely water-insoluble. These results demonstrate the critical importance of tailgroup geometry on surfactant properties and self-assembly for this industrially important class of surfactants.
长链丙基甜菜碱以能够自组装成粘弹性蠕虫状胶束结构而闻名。在这里，我们研究了尾基分子结构对这一过程的影响，比较了五种分子，它们都具有 C18 链，但不饱和程度和支化程度不同。这些表面活性剂是由硬脂酸、油酸、亚油酸、亚麻酸和异硬脂酸合成的。使用小角和超小角中子散射（SANS 和 USANS）研究了这些分子在水溶液中的自组装。结果表明，油酸链表面活性剂最适合形成蠕虫状胶束，并且使用流变学 SANS 进一步探索了自组装结构的取向。具有更高不饱和度的分子形成棒状胶束，而硬脂酸尾链分子表现出明显的克拉夫特点，异硬脂酸链表面活性剂则完全不溶于水。这些结果表明，尾基几何形状对这类工业上重要的表面活性剂的表面活性剂性质和自组装具有至关重要的影响。
