Collaborative Research: Simple Paradigms for Understanding Viscosity in Ionic Liquids

这项由爱荷华州大学的马古里斯教授和罗格斯大学的卡斯特纳教授联合开展的项目，由美国国家科学基金会化学结构和动力学机制(CSDM-A)项目资助，其首要目标是了解一类特殊液体的分子结构如何决定其粘度。粘度是衡量液体流动情况的指标(例如，纯蜂蜜比水更粘稠)。Marguis教授和Castner教授对离子液体(ILS)特别感兴趣。ILS是一种独特的材料；像食盐一样，它们只由正(阳离子)和负离子(阴离子)物种组成，但与食盐不同，食盐在环境条件下是固体，它们在室温下是液体。了解和控制离子液体的粘度之所以重要，与它们作为润滑剂、工业过程中的溶剂或先进电池材料的许多可能的应用有关。在微观长度尺度上，这些液体是复杂的，正负电荷网络被不带电的区域隔开。研究小组正在使用包括计算机模拟、核磁共振以及X射线和中子散射在内的一系列技术来解决这些具有挑战性的问题。这项研究的研究人员从本科生到研究生再到博士后研究员，每个人都在实验和理论工具方面做出了贡献并获得了独特的经验。离子液体最紧迫的问题之一是如何控制其在特定应用中的粘度。这些液体在结构和动力学上都是非均相的，电荷网络是更坚硬的成分，其中电荷交替模式随时间的松弛直接与粘度有关。研究小组正试图了解这种“电荷模糊”过程是如何发生的。为此，他们使用了理论计算和分子动力学模拟以及X射线散射、中子散射技术和核磁共振技术，这些技术允许对不同液体结构基元的动力学进行时间分辨。最终目标是得出一个预测性的和图示的观点，说明是什么导致了特定ILS的粘度。这项研究的更广泛的影响是多方面的；它们包括为研究ILS的研究人员社区提供关于如何在不同的科学和技术应用中控制粘度的理解。除了为研究生和博士后研究员提供正式培训外，该项目还为本科生提供研究经验，包括一些来自昆士伯勒社区学院的学生。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The overarching goal of the joint project by Professors Margulis (U. of Iowa) and Castner (Rutgers), funded by the NSF Chemical Structure and Dynamics Mechanisms (CSDM-A) program, is to understand how the molecular structure of a special class of liquids determines their viscosity. Viscosity is a measure of how well a liquid flows (for example, pure honey is more viscous than water). Professors Margulis and Castner are specifically interested in Ionic Liquids (ILs). ILs are unique materials; like table salt they are solely composed of positive (cationic) and negative (anionic) species, but unlike table salt, which is a solid at ambient conditions, they are liquids at room temperature. The reason why understanding and controlling the viscosity of ILs is important relates to their many possible applications as lubricants, as solvents for industrial processes or in advanced battery materials. On a microscopic length scale these liquids are complex, with networks of positive and negative charges separated by uncharged domains. The research team is using a battery of techniques including computer simulations, nuclear magnetic resonance, as well as X-ray and neutron scattering to attack these challenging questions. Researchers in this study range from undergraduate level students to graduate students to postdoctoral fellows, each contributing and gaining unique experiences on experimental and theoretical tools. One of the most pressing questions about ionic liquids is how to control their viscosity for specific applications. These liquids are structurally and dynamically heterogeneous with networks of charge being the stiffer component, and it is the relaxation with time of the charge alternation pattern within these that is directly linked to viscosity. The research team is seeking to understand how this process of “charge-blurring” occurs. For this, they are using theoretical calculations and molecular dynamics simulations as well as X-ray scattering, neutron scattering techniques that allow for temporal resolution of the dynamics of the different liquid structural motifs, and NMR techniques. The ultimate goal is to derive a predictive and pictorial view of what causes the viscosity for specific ILs. The broader impacts of the study are manifold; they include supplying the community of researchers working on ILs with an understanding of how viscosity might be controlled for different scientific and technological applications. In addition to providing formal training for graduate students and post-doctoral fellows, the project is providing research experience for undergraduate students, including some from Queensborough Community College.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.