Collaborative Research: Ionic Liquids at Interfaces: from Bulk Structure to Tunable Films

美国国家科学基金会化学部的化学结构、动力学和机制项目（CSDM-A）支持由爱荷华大学的Claudio J. Margulis教授和新泽西州立大学罗格斯分校的Edward W. Castner, Jr.（合作P.I.）与昆斯伯勒社区学院的Sharon Lall-Ramnarine教授合作进行的一项合作研究。本研究的重点是对一类特殊液体离子液体的分子水平结构有更全面的了解。离子液体因其在电池和气体分离系统等各种技术中的潜在应用而引起人们的兴趣。马古利斯教授和卡斯特纳教授正在研究离子液体的分子结构如何影响它们的“厚度”（粘度）和电导率等特性。离子液体是一类有趣的化合物，像盐一样由带正电的原子或分子（阳离子）和带负电的原子或分子（阴离子）组成。离子液体是在室温或接近室温时熔化的盐。这项研究涉及实验技术（如x射线光谱学和合成）和计算机建模。该研究项目有望增加我们对离子液体性质的理解，使它们能够更好地应用于现代储能技术中的各种问题，以及其他新颖的应用。参与该研究项目的学生在一个高度跨学科的环境中获得经验，以非传统的方式挑战研究生。例如，马古利斯小组的学生，他们的兴趣和专长主要是理论和计算，他们花时间在卡斯特纳实验室，在那里他们获得实际实验的经验。与此同时，来自Castner小组的实验主义研究生研究人员正在马古利斯教授的指导下进行模拟工作。最后，昆斯伯勒社区学院的合作项目将为来自少数族裔服务机构的本科生提供研究经验。液体可以在不同的长度尺度上表现出结构秩序，从两个分子之间简单的成对相互作用到可以延伸到几纳米的氢键网络。离子液体已被证明具有中间范围的结构秩序，这是由带正电的阳离子和带负电的阴离子之间的强相互作用结合而产生的，这些分子离子上有疏水性基团。马古利斯和卡斯特纳小组最近的一些工作表明，离子液体可以被设计成这种中间范围的秩序被破坏。这种结构破坏与较低的粘度有关，这为增强型电池和电双层技术的优质电解质的开发提供了机会。在这个项目中，马古利斯和卡斯特纳的团队正在试图了解具有特定离子组合的离子液体是否会进一步破坏中间范围的秩序。计算分子动力学研究指导和解释实验结果，包括同步加速器（如阿贡国家实验室的先进光子源）的高能x射线实验，使用核磁共振技术测量离子扩散率，以及密度和粘度实验。该项目的另一个重要方面是获得离子液体阴离子和阳离子在真空或特定固体界面中的排列的定量理解。Castner小组正在将体积液体模拟扩展到真空界面，而角度分辨x射线光电子能谱测量则提供了界面上特定原子的密度分布图。马古利斯和卡斯特纳团队继续参与离子液体的计算研究和基于同步加速器的x射线实验，为年轻科学家提供了出色的协作交叉训练研究经验。Lall-Ramnarine教授和她的学生为社区大学生提供了第一次研究经验。

The Chemical Structure, Dynamics and Mechanisms Program of the NSF Chemistry Division (CSDM-A) supports a Collaborative Research effort by Professors Claudio J. Margulis at the University of Iowa (P.I.) and Edward W. Castner, Jr. (co-P.I.) at Rutgers, The State University of New Jersey, with synthetic collaborations including Professor Sharon Lall-Ramnarine at Queensborough Community College. The focus of this research is to develop a more complete understanding of the molecular level structure of a special class of liquids called ionic liquids. Ionic liquids are gaining interest for their potential applications in various technologies for example, batteries and gas separation systems. Professors Margulis and Castner are studying how the molecular structure of ionic liquids affects such properties as their "thickness" (viscosity) and electrical conductivity. Ionic liquids are an interesting class of compounds that, like salts are composed of positively charged atoms or molecules (cations) and negatively charged atoms or molecules (anions). Ionic liquids are salts that are molten at or near room temperature. The research involves both experimental techniques (e.g., x-ray spectroscopy and synthesis) and computer modeling. The research project is expected to increase our understanding of ionic liquid properties, so that they can be better applied to a variety of problems in modern energy storage technologies, as well as other novel applications. The students involved in this research project are gaining experience in a highly interdisciplinary environment that challenges graduate students in non-traditional ways. For example, students in the Margulis group whose interests and expertise are primarily in theory and computation spend time in the Castner laboratory, where they gain experience in actual experiments. At the same time, the experimentalist graduate researchers from the Castner group are doing simulation work under Prof. Margulis' guidance. Finally, the Queensborough Community College collaboration is providing research experiences for selected undergraduate students from a minority-serving Associates-level institution. Liquids can exhibit structural order at various length scales, from simple pair-wise interactions between two molecules to hydrogen-bonded networks that may extend over several nanometers. Ionic liquids have been shown to have an intermediate range of structural order arising from the combination of the strong interactions between the positively charged cations and the negatively charged anions, with hydrophobic groups on these molecular ions. Some of the Margulis and Castner groups' recent work has shown that ionic liquids can be designed such that this intermediate range order is disrupted. Such structural disruptions are correlated to lower viscosities, which provide opportunities for the development of superior electrolytes for both enhanced battery and electrical double-layer technologies. In this project, the Margulis and Castner teams are seeking to understand whether ionic liquids with certain combinations of ions will further disrupt intermediate range order. Computational molecular dynamics studies guide and explain experimental results, including those from high-energy X-ray experiments at synchrotrons (such as the Advanced Photon Source at Argonne National Laboratory), from measurement of ion diffusivities using nuclear magnetic resonance techniques, and density and viscosity experiments. Another important aspect of the project is to obtain a quantitative understanding of the arrangement of the ionic liquid anions and cations in vacuum or specific solid interfaces. The Castner group is extending the bulk liquid simulations to include vacuum interfaces, while angle-resolved X-ray photoelectron spectroscopy measurements are providing the density profiles of specific atoms at the interface. Both the Margulis and Castner groups continue to participate in both computational studies of ionic liquids and synchrotron-based X-ray experiments, providing excellent collaborative cross-training research experiences for younger scientists. Inclusion of Professor Lall-Ramnarine and her students provides a first research experience for community college students.