Biology and Soft Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
Soft Matter. 2017 Oct 11;13(39):7154-7160. doi: 10.1039/c7sm01516j.
Mixtures of water, octane and 1-octanol with 1-tetradecyl-3-methylimidazolium chloride (CMIM·Cl), often referred to as a surface active ionic liquid (SAIL), form water-in-oil microemulsions that have potential application as extraction media for various metal ions. Here, we present a structural study by small-angle neutron scattering (SANS) of dense microemulsions formed by surfactant-rich mixtures of these four compounds to understand how the SAIL can be used to tune the structures and properties of the microemulsions. The SANS experiments revealed that the microemulsions formed are composed of two phases, a water-in-oil microemulsion and a bicontinuous microemulsion, which becomes the dominant phase at high surfactant concentration. In this concentration regime, the surfactant film becomes more rigid, having a higher bending modulus that results from the parallel stacking of the imidazolium ring of the SAIL. At lower surfactant concentrations, the molecular packing of the SAIL does not change with the water content of the microemulsion. The results presented here correlate well with previously observed changes in the interaction between the IL cation and metal ions (Y. Tong, L. Han and Y. Yang, Ind. Eng. Chem. Res., 2012, 51, 16438-16443), while the capacity of the microemulsion system for water remains high enough for using the system as an extraction medium.
水、辛烷和 1-辛醇与 1-十四烷基-3-甲基咪唑氯盐（CMIM·Cl）的混合物，通常称为表面活性离子液体（SAIL），形成油包水乳状液，具有作为各种金属离子萃取介质的潜在应用。在这里，我们通过小角中子散射（SANS）研究了由这四种化合物的富含表面活性剂的混合物形成的密集微乳液的结构，以了解 SAIL 如何用于调节微乳液的结构和性质。SANS 实验表明，形成的微乳液由两相组成，即油包水乳状液和双连续乳状液，在高表面活性剂浓度下，双连续乳状液成为主要相。在该浓度范围内，表面活性剂膜变得更加刚性，具有更高的弯曲模量，这是由于 SAIL 的咪唑环的平行堆积所致。在较低的表面活性剂浓度下，微乳液的含水量不会改变 SAIL 的分子堆积。这里呈现的结果与之前观察到的 IL 阳离子与金属离子之间相互作用的变化很好地相关（Y. Tong, L. Han and Y. Yang, Ind. Eng. Chem. Res., 2012, 51, 16438-16443），而微乳液系统对水的容量仍然足够高，可以将该系统用作萃取介质。
