Ionic liquid microdroplets as versatile lithographic molds for sculpting curved topographies on soft materials...

Soft lithography comprises a set of approaches for shaping the surface of soft materials such as PDMS on the microscopic scales. These procedures usually begin with the development of templates/masters normally generated by electron or photolithography techniques. However, the richness in available shapes is limited, usually producing shapes containing sharp parts. Innovation is called for to develop reliable approaches capable of imparting well-defined 3D curved shapes to these solids, a topology that is somehow unnatural for solid surfaces. Here we report on the use of tiny drops of room-temperature ionic liquid, organic liquids that have attracted increasing amounts of attention in recent years because of their unique chemical properties) as a versatile platform for imprinting PDMS with tunable 3D curved geometry, which is out of reach of conventional lithographic techniques and ranges from almost flat depressions to almost closed cavities on the millimeter to micrometer scale. The concept exploits a peculiar combination of physical properties displayed by ionic liquids as their null volatility and their polarity, together with some unique properties of liquid surfaces as their virtually null surface roughness. Proof-of-concept experiments show their application as chemical microreactors and ultrasmooth optical lenses. This all-liquid method is simple, low-cost, versatile, maskless, tension-free, and easily scalable, so we envision a community-wide application in numerous modern physical, chemical, biological, and engineering settings.