Department of Chemistry, University of Bath , Claverton Down, Bath BA2 7AY, U.K.
European Spallation Source , Box 176, 22100 Lund, Sweden.
Langmuir. 2017 Dec 19;33(50):14304-14314. doi: 10.1021/acs.langmuir.7b03254. Epub 2017 Dec 8.
Deep eutectic solvents have been demonstrated to support amphiphile self-assembly, providing potential alternatives as structure-directing agents in the synthesis of nanostructures, and drug delivery. Here we have expanded on this recent research to investigate the self-assembly of alkyltrimethylammonium bromide surfactants in choline chloride:malonic acid deep eutectic solvent and mixtures of the solvent with water. Surface tension and small-angle neutron scattering were used to determine the behavior of the amphiphiles. Surfactants were found to remain active in the solvent, and surface tension measurements revealed changes in the behavior of the surfactants with different levels of hydration. Small-angle neutron scattering shows that in this solvent the micelle shape depends on the surfactant chain length, varying from globular micelles (aspect ratio ∼2) for short chain surfactants to elongated micelles (aspect ratio ∼14) for long chain surfactants even at low surfactant concentration. We suggest that the formation of elongated micelles can be explained through the interaction of the solvent with the surfactant headgroup, since ion-ion interactions between surfactant headgroups and solvent may modify the morphology of the micelles. The presence of water in the deep eutectic solvents promotes an increase in the charge density at the micelle interface and therefore the formation of less elongated, globular micelles.
深共晶溶剂已被证明可支持两亲分子自组装，为纳米结构合成和药物输送中的结构导向剂提供了潜在的替代品。在这里，我们扩展了这项最近的研究，以研究氯化胆碱：丙二酸深共晶溶剂中和溶剂与水的混合物中烷基三甲基溴化铵表面活性剂的自组装。表面张力和小角中子散射被用来确定两亲分子的行为。结果表明，表面活性剂在溶剂中仍然保持活性，表面张力测量揭示了不同水合程度的表面活性剂行为的变化。小角中子散射表明，在这种溶剂中，胶束形状取决于表面活性剂链长，短链表面活性剂的胶束形状为球形（纵横比约为 2），而长链表面活性剂的胶束形状为拉长的（纵横比约为 14），即使在低表面活性剂浓度下也是如此。我们认为，通过溶剂与表面活性剂头基的相互作用可以解释长形胶束的形成，因为表面活性剂头基之间的离子-离子相互作用可能会改变胶束的形态。水在深共晶溶剂中的存在促进了胶束界面处电荷密度的增加，从而形成了不那么拉长的、球形的胶束。
