Formation of Surface Protic Ionic Liquid Nanodroplets for Nanofabrication

Abstract

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.

Adsorption, Wetting, Growth, and Thermal Stability of the Protic Ionic Liquid Diethylmethylammonium Trifluoromethanesulfonate on Ag(111) and Au(111)

“…13,14 This is not possible with conventional molecular liquids due to their typically finite vapor pressure. 14 Fundamental knowledge on the PIL/solid interaction and wetting characteristics is essential for understanding and tailoring the formation of such nanodroplets, and for rationalizing the sometimes unexpected interfacial properties of PILs. 5 Other interesting applications are heterogeneous metal catalysis using PILs, 15,16 batteries with PIL electrolyte, 17,18 biomass processing with PILs, 19,20 in palladium in PIL electrolyte, 21 and metal nanoparticle synthesis in PILs.…”

“…Information on the adsorption, wetting, and growth of PILs on solid substrates also is highly relevant for applications like nanofabrication. On the basis of the very low vapor pressure of ILs in general, , stable nanodroplets of PILs on solid supports have recently been used for templating nanostructures. , This is not possible with conventional molecular liquids due to their typically finite vapor pressure . Fundamental knowledge on the PIL/solid interaction and wetting characteristics is essential for understanding and tailoring the formation of such nanodroplets, and for rationalizing the sometimes unexpected interfacial properties of PILs .…”

Surface nanodroplet-based nanoextraction from sub-milliliter volumes of dense suspensions

“…In the literature, solvent exchange has been applied for forming droplets of unconventional liquids such as extremely viscous silicone elastomers 63 or ionic liquids. 64 We expect that these droplets can be formed on capillary tubes as well since the principle of droplet nucleation and growth is the same regardless of chamber geometry. Formation of droplets with various extractant liquids expands the type of chemicals that can be extracted and analyzed, as extraction of certain analytes can depend on the extractant type.…”

Acid and Base Water Coexists in a Micro‐Structured Ionic Liquid and Catalyzes Organic Reactions in One‐Pot

“…The liquid system allows to perform acid/base catalyzed cascade reactions in water [16] with the simplest acid and bases, i. e. HCl and KOH, and others. The additive-free formation of pH tunable water microdroplets can have further applications not only in catalysis but also in fundamental biological [17] and physicochemical [18] studies, including for instance nanofabrication [19] and optics. [20]…”