Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford OX1 3QZ, UK.
Department of Physics, Scottish Universities Physics Alliance (SUPA), Strathclyde University, John Anderson Building, 107 Rottenrow East, Glasgow G4 0NG, UK and Skolkovo Institute of Science and Technology, Skolkovo Innovation Center, Moscow 143026, Russia.
Faraday Discuss. 2018 Jan 1;206:427-442. doi: 10.1039/c7fd00168a. Epub 2017 Sep 21.
Many applications of ionic liquids involve their mixtures with neutral molecular solvents. The chemical physics of these high-concentration electrolytes, in particular at interfaces, still holds many challenges. In this contribution we begin to unravel the relationship between measurements of structural ('solvation') forces in mixtures of ionic liquid with polar solvent and the corresponding structure determined by molecular dynamics simulations of the same mixtures. In order to make the quantitative link between experiments with mica surfaces and simulations with fixed-charge surfaces, we present an experimental procedure for determining the effective surface charge on mica in ionic liquid. We find that a structural cross-over recently inferred from force measurements appears to be supported by the simulations: at the cross-over, the charge-oscillatory structure switches to charge-monotonic, and solvent layering becomes dominant. Finally, we map out a phase diagram in composition-surface charge space delineating regions of charge-oscillatory interfacial structure and regions of charge-monotonic decay. We note that these features of structure and oscillatory forces are distinct from (acting simultaneously with) the recently reported longer range monotonic forces arising from anomalously long bulk screening lengths in high-concentration electrolytes.
许多离子液体的应用都涉及它们与中性分子溶剂的混合物。这些高浓度电解质的物理化学性质，特别是在界面处，仍然存在许多挑战。在本研究中，我们开始揭示离子液体与极性溶剂混合物中结构（“溶剂化”）力测量值与相同混合物的分子动力学模拟确定的结构之间的关系。为了在云母表面的实验和固定电荷表面的模拟之间建立定量联系，我们提出了一种在离子液体中确定云母有效表面电荷的实验程序。我们发现，最近从力测量中推断出的结构交叉似乎得到了模拟的支持：在交叉处，电荷振荡结构转变为电荷单调结构，溶剂分层变得占主导地位。最后，我们在组成-表面电荷空间中绘制了一个相图，描绘了电荷振荡界面结构和电荷单调衰减的区域。我们注意到，这些结构和振荡力的特征与（同时作用）最近报道的源于高浓度电解质中异常长的体相屏蔽长度的长程单调力不同。
