Influence of Structure, Interionic Interactions, Interfacial slip and Viscous-electric Coupling Phenomena on the Rheology of Nanoconfined Ionic Liquids

该项目的总体目标是推进对离子液体的结构-性质关系的认识，离子液体是具有可调成分的有机熔盐。除了离子电导率高外，离子液体还具有挥发性低、热稳定性好、可燃性低、电化学窗口宽等特点。与现有技术相比，这些特性可以使安全的能量存储设备具有更高的能量和功率密度以及更长期的稳定性。然而，这些器件的性能取决于离子液体在极窄空间中的粘度，而它们的高粘度与电导率和电容降低、多孔电极润湿性差以及功率密度降低有关。因此，研究纳米离子液体的流动特性是至关重要的。该项目将研究纳米尺度通道中液体成分与流动行为之间的关系。因此，它将能够建立离子液体作为下一代超级电容器和电池技术的电解质的设计原则。拟议的研究还将通过培训两名材料化学与工程、界面科学和流变学交叉领域的研究生研究助理，为美国劳动力的发展做出贡献。这种多学科的方法将有助于扩大未被充分代表的群体在研究中的参与，并有利于工程教育。该研究项目将解决纳米约束离子液体流动中的三个主要问题：液体结构与纳米流变性之间的关系，表面组成（润湿性）和纳米尺度粗糙度对材料行为的影响，以及静电和粘性现象之间的联系。实验研究将使用表面力装置，将液体限制在两个具有受控特性的表面之间。静力和水动力以及动态剪切的测量将在一组精心选择的具有广泛成分的离子液体上进行。这些研究结果将用于开发一个框架来预测纳米限制离子液体的流变学。此外，这项研究产生的知识将使从业者能够通过精确控制离子液体的结构、表面润湿性、粗糙度和电位来调节离子液体的纳米流变响应。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。

The overall goal of this project is to advance the knowledge about structure-property relationships for ionic liquids, which are organic molten salts with tunable compositions. Besides high ionic conductivity, ionic liquids exhibit low volatility, good thermal stability, low flammability, and a wide electrochemical window. These properties could enable safe energy storage devices with higher energy and power density and longer-term stability than is possible with current technologies. However, the performance of these devices depends on the viscosity of the ionic liquids in extremely narrow spaces, and their high viscosity has been linked to reduced electrical conductivity and capacitance, poor wetting of porous electrodes, and lower power density. Therefore, research that addresses the flow characteristics of nanoconfined ionic liquids is of paramount importance. This project will examine the relationship between liquid composition and flow behavior in nanoscale channels. Thereby, it will enable to establish design principles of ionic liquids as electrolytes for next-generation supercapacitor and battery technologies. The proposed research will also contribute to the development of the US work force by training two graduate research assistants at the intersection between materials chemistry and engineering, interfacial science, and rheology. This multi-disciplinary approach will help broaden participation of underrepresented groups in research and benefit engineering education. The research project will address three major issues in the flow of nanoconfined ionic liquids: the relationship between liquid structure and nanorheology, the effects of surface composition (wettability) and nanoscale roughness on material behavior, and the connection between electrostatic and viscous phenomena. The experimental study will use a surface forces apparatus by confining the liquids between two surfaces with controlled characteristics. Measurements of static and hydrodynamic forces as well as dynamic shear will be carried out on a set of judiciously selected ionic liquids with a wide range of compositions. The findings of these studies will be used to develop a framework to predict the rheology of nanoconfined ionic liquids. Furthermore, the knowledge generated by this research will enable practitioners to modulate the nanorheological response of ionic liquids through the precise control of their structure, surface wettability, roughness and potential.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.