Ions at aqueous interfaces: X-ray fluorescence and scattering studies

非技术描述：水中的盐溶液在我们的身体、食物和饮料、海洋以及日常生活的其他地方发挥着至关重要的作用。这些令人着迷的软物质系统包含了许多惊喜。溶解离子的行为非常复杂，在这种体系中已经观察到一些显著的意想不到的行为。例如，溶解的离子被认为非常相似，如钠和钾，以完全不同的方式影响聚合物和蛋白质分子----这被称为“特定离子效应”。另一种意想不到的现象被称为过充电或电荷反转：在某些条件下，水中的分子或油滴会改变其电荷的符号，从而在电场存在的情况下开始向“错误”的方向移动。在这个项目中，来自同步辐射设备的x射线束被用来获得这些系统的亚纳米级定量视图，从而揭示这些新现象的起源。技术描述：本提案解决了水溶液界面附近离子行为的基本问题。戈伊-查普曼-斯特恩理论描述了这些离子的分布，但没有适当地解释离子电荷的离散性，而且越来越多的证据表明，它在许多情况下是失败的。然而，对于它失败的原因以及如何发展出一幅更普遍的图景，人们并没有达成共识。该项目的目标是研究纳米级离子结构和过程，这些结构和过程是电荷反转（也称为过充电）和特定离子效应（如Hofmeister系列）等非直观现象的基础。在本研究中使用的主要实验探针是x射线散射和荧光光谱，使用同步辐射。水溶液中的离子影响胶体、聚合物、电池和一些电容器以及许多其他日常材料和设备的行为。溶解的离子影响膜的物理性质，改变蛋白质和DNA的行为；事实上，它们对生命至关重要。所有这些过程都得益于对水溶液中离子如何在界面附近排列的纳米级理解。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical Description:Solutions of salts in water play essential roles in our bodies, in food and drink, in the ocean, and elsewhere in everyday life. These are fascinating soft matter systems that contain many surprises. The behavior of dissolved ions is quite complex, and some remarkable unexpected behaviors have been observed in such systems. For example, dissolved ions that are thought to be very similar, such as sodium and potassium, affect polymer and protein molecules in completely different ways ----this is known as a ‘specific ion effect’. Another unexpected phenomenon is known as overcharging or charge inversion: under certain conditions, molecules or oil droplets in water will change the sign of their electric charge, and thus start moving in the ‘wrong’ direction in the presence of an electric field. In this project, X-ray beams from synchrotron radiation facilities are used in order to gain a subnanoscale quantitative view of these systems and thus shed light on the origins of these novel phenomena. Technical Description:This proposal addresses fundamental questions regarding the behavior of ions near aqueous solution interfaces. Gouy-Chapman-Stern theory describes the distribution of such ions, but does not properly account for the discreteness of ionic charge, and there is increasing evidence that it fails in many cases. However, there is no consensus about why it fails and how to develop a more universal picture. The goal of this project is to study the nanoscale ionic structures and processes underlying the nonintuitive phenomena of charge inversion (also known as overcharging), and specific ion effects (such as the Hofmeister series). The primary experimental probes used in this research are X-ray scattering and fluorescence spectroscopy, using synchrotron radiation. Ions in aqueous solution affect the behavior of colloids, polymers, batteries and some capacitors, and many other everyday materials and devices. Dissolved ions affect the physical properties of membranes and modify the behavior of proteins and DNA; indeed they are crucial to life. All these and other processes benefit from a better nanoscale understanding of how ions in aqueous solutions arrange themselves near interfaces.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.