Department of Materials Science and Engineering, Northwestern University , Evanston, Illinois 60208, United States.
Chemical Sciences & Engineering Division, Argonne National Laboratory , Argonne, Illinois 60439, United States.
Langmuir. 2017 Jun 20;33(24):6135-6142. doi: 10.1021/acs.langmuir.7b01230. Epub 2017 Jun 7.
Interfacial liquid-liquid ion transport is of crucial importance to biotechnology and industrial separation processes including nuclear elements and rare earths. A water-in-oil microemulsion is formulated here with density and dimensions amenable to atomistic molecular dynamics simulation, facilitating convergent theoretical and experimental approaches to elucidate interfacial ion transport mechanisms. Lutetium(III) cations are transported from the 5 nm diameter water pools into the surrounding oil using an extractant (a lipophilic ligand). Changes in ion coordination sphere and interactions between the interfacial components are studied using a combination of synchrotron X-ray scattering, spectroscopy, and atomistic molecular dynamics simulations. Contrary to existing hypotheses, our model system shows no evidence of interfacial extractant monolayers, but rather ions are exchanged through water channels that penetrate the surfactant monolayer and connect to the oil-based extractant. Our results highlight the dynamic nature of the oil-water interface and show that lipophilic ion shuttles need not form flat monolayer structures to facilitate ion transport across the liquid-liquid interface.
界面液-液离子输运对于生物技术和工业分离过程（包括核素和稀土元素）至关重要。本文设计了一种具有合适密度和尺寸的油包水乳状液，适用于原子分子动力学模拟，从而促进收敛的理论和实验方法来阐明界面离子输运机制。镥(III)阳离子通过萃取剂（亲脂配体）从 5nm 直径的水相中传输到周围的油相中。利用同步加速器 X 射线散射、光谱和原子分子动力学模拟相结合的方法，研究了离子配位层和界面组分之间相互作用的变化。与现有假说相反，我们的模型系统没有证据表明存在界面萃取剂单层，而是通过穿透表面活性剂单层并与油基萃取剂连接的水通道来交换离子。我们的结果突出了油水界面的动态性质，并表明亲脂离子穿梭体不必形成平坦的单层结构即可促进离子在液-液界面的传输。
