Interfacial ordering in aqueous solutions: X-ray scattering studies

溶解在水中的非技术抽象决定了胶体（包括从沙拉酱到油漆的商业产品）的性质。电极和离子溶液之间的界面是电池、超级电容器和其他设备的关键部分。周围的离子影响膜的物理性质，改变蛋白质和DNA的行为。了解界面上离子的结构和性质对于从水中提取离子至关重要，无论是用于脱盐，从地下水或废水中去除铅，砷或放射性元素，还是增加现代电子产品的稀土材料供应。所有这些系统和过程都将受益于一个更好的纳米尺度的观点，即离子是如何在潮湿的表面附近排列的。这个项目使用同步加速器x射线直接观察离子是如何在潮湿表面附近排列的，同时改变表面、离子、浓度、温度等。从这项研究中学到的东西将有助于验证或反驳理论预测，并可能最终帮助设计具有实际应用的特定属性的系统。该项目在跨学科的环境中培养研究生，并使他们获得使用同步加速器设备的经验。与项目相关的主题已被纳入本科和研究生课程，并在网上发布教材。技术摘要：在含有离子的水溶液中观察到各种新颖和/或违反直觉的行为。例如，带电界面有时会吸引比简单静电学预测的更多的反离子（“电荷反转”）。虽然疏水（非极性）表面排斥水，但它们被认为吸引某些离子到界面。离子在界面和大分子周围的作用可能具有很强的离子特异性，例如，不同的镧系元素的行为非常不同。例如，在从溶液中提取镧系元素和锕系元素的液-液分离过程中，利用了这种效应，但其起源尚不清楚。这些异常行为可能有构造成因。在这个项目中进行了界面的x射线散射研究，其中界面的一侧是含有离子的溶液。目的是表征与界面垂直的分布，并了解离子是否以及在什么条件下横向有序形成具有改性性质的凝聚界面相。该项目在跨学科的环境中培养研究生，并为他们提供使用同步加速器设施的经验。与液体相关的主题正在被纳入本科和研究生课程以及网络传播的教材中。

Nontechnical abstractIons dissolved in water determine the properties of colloids (including commercial products ranging from salad dressings to paint). The interface between an electrode and an ionic solution is a crucial part of batteries, supercapacitors and other devices. Surrounding ions affect the physical properties of membranes and modify the behavior of proteins and DNA. Understanding the structure and properties of ions at interfaces is crucial to extracting them from water, whether for desalinization, removal of lead, arsenic or radioactive elements from groundwater or wastewater, or increasing the supply or rare earth materials for modern electronics. All these systems and processes would benefit from a better nanoscale view of how ions actually arrange themselves near wet surfaces. This project uses synchrotron X-rays to look directly at how ions are arranged near wet surfaces, while varying the surface, the ion, the concentration, the temperature, etc. What is learned from this research will help verify or refute theoretical predictions, and may also ultimately help design systems with specific properties for practical applications. This project trains graduate students in an interdisciplinary environment and gives them experience in the use of synchrotron facilities. Project-related topics are being incorporated into undergraduate and graduate courses and web-disseminated teaching materials.Technical abstractA variety of novel and/or counterintuitive behaviors have been observed in aqueous solutions containing ions. For example, charged interfaces sometimes attract more counterions than simple electrostatics would predict ("charge inversion"). Though hydrophobic (nonpolar) surfaces repel water, they are thought to attract certain ions towards the interface. The effects of ions at interfaces and around macromolecules can be strongly ion-specific, e.g. different lanthanides behave very differently. Such effects are exploited, for example, in liquid-liquid separations processes used to extract lanthanides and actinides from solution, but the origins are not understood. These anomalous behaviors are likely to have structural origins. X-ray scattering studies of interfaces, where one side of the interface is a solution containing ions, are performed in this project. The goal is to characterize the distributions normal to the interfaces, and also to understand whether and under what conditions the ions order laterally to form condensed interfacial phases with modified properties. The project trains graduate students in an interdisciplinary environment and gives them experience in the use of synchrotron facilities. Liquids-related topics are being incorporated into undergraduate and graduate courses and web-disseminated teaching materials.