Formation of Surface Protic Ionic Liquid Nanodroplets for Nanofabrication

Femtoliter droplets at solid interfaces attract significant interest as the basic units in many physical and biological processes. One challenge in the application of these tiny droplets is their fast evaporation rate in air due to their large surface-to-volume ratio. Ionic liquids with low volatility present an opportunity to overcome this challenge. The advanced properties of ionic liquids (ILs) have enabled them to be widely applied in chemical reactions, biopolymers, molecular self-assembly and separations. At interfaces, the wettability of ILs is pursued in next-generation lubricants and battery technology. Previously, IL droplets at solid surfaces have been prepared by nanodispensing, micropipette, and solvent evaporation. Here, the solvent exchange protocol is extended to yield protic ionic liquid droplets at the interface with controlled size, distribution, location, and stability in both liquid and air surroundings. During growth, the droplets demonstrate an interesting dewetting dynamic. This behavior has not been observed for molecular liquids during solvent exchange and suggests interesting interfacial dynamics of the ionic liquid. One proof-of-concept application of using surface nanodroplets of the protic ionic liquid ethylammonium nitrate for compartmentalized reactions and templating SiO2 nanostructures is demonstrated. This work broadens and intertwines the opportunities of ILs and nanodroplets.