The properties of ionic liquids (ILs) near a charged solid-liquid interface are of great importance to applying ILs as electrolytes, lubricants, and solvents. Recent advances in the surface science community indicate gaps in the current understanding of the interfacial structures in ILs and concentrated electrolytes. In the present study, we conduct direct force measurement on the IL-solid interface with a surface force apparatus (SFA) operated in two different modes. The ILs are either compressed in the direction normal to the confining mica surfaces or sheared laterally. By fitting the force- distance curves to a constitutive model, we deconvolute the contributions of various nano-scale interactions within ILs. Through rheology measurements, we investigate the presence of nanoscale assemblies. Coupling the normal-force measurements with the rheology measurements, we infer on the nano structures of ILs at the charged solid-liquid interface. In addition, water in introduced in to the nano-confined ILs as a molecular probe to modify the interionic interactions. The findings will shed light on the paradox of electrical double layers of concentrated electrolytes, and provide practical hints for designing IL-based devices exposed to ambient humidity.

Understanding the IL-solid interface using water as molecular probes

2019 Fall National Meeting

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