Manipulating Oil Droplets by Superamphiphobic Nozzle.

Abstract

will be reduced and liquid retention on such nozzles is to be avoided, which is of great importance to the development of tiny oil droplets fabrication. We have prepared a superhydrophobic needle nozzle to manipulate water droplets. [ 13 ] However, most functional materials for fabrication of organic solar cells, organic fi eld effect transistors, and organic light-emitting diodes are only soluble in organic liquids with low surface tensions. As organic liquid will spread and wet the water repellent surface, the superhydrophobic nozzle is not able to manipulate such low surface tension liquids. Thus, it is still a challenge to increase the liquid transfer effi ciency of organic liquid. Here, we report a facile strategy to manipulate small organic liquid droplets assisted by a superamphiphobic nozzle. Owing to the superliquid-repellent property of the nozzle surface, oil droplet is restricted at the edge of the nozzle, which avoids the spreading of oil droplet and results in decreased volume as well as increased liquid transfer effi ciency. Furthermore, by utilizing the superliquid-repellent nozzle to directly dispense oil-based inks, high-resolution 3D structures are fabricated, which is of great signifi cance for the development of liquid transportation and ink-jet printing devices. Figure 1 a shows the preparation process of the hierarchically structured superamphiphobic nozzle surface. Copper plates (5 × 5 × 1 mm 3 ) were used as the base material for nozzle fabrication, and holes were drilled through the plates for tiny oil droplet dispensing. Holes with diameters ranged from 20 to 150 μm were prepared by laser drilling (Figure 1 b), and holes larger than 150 μm were fabricated by mechanical drilling (Figure 1 c). To modify the nozzle surface with reentrant micronanostructures, chemical base corrosion was performed, [ 14 ] in which Cu plates were immersed in an ammonium persulfate and sodium hydroxide mixture solution (details about the morphology and wettability of different corrosion time can be seen in Figures S1 and S2, Supporting Information). As shown in Figure 1 d, Cu(OH) 2 microsheets and microclusters with re-entrant structures are achieved. Since surface wettability is controlled by both surface morphology and surface chemical composition, [ 15 ] only a structured route is not enough to realize superamphiphobicity on the nozzle surface. Fluorination was thus used to lower the surface energy. X-ray photoelectron spectroscopy (XPS) spectra demonstrated the successful introduction of fl uorine element on the prepared surface and the conversion of Cu(OH) 2 to Cu(O 2 C 2 H 2 C 8 F 17 ) 2 (Figure S3, Supporting Information). In addition, scanning electron microscope (SEM) images showed that almost no visual morphology change occurred after fl uorination (Figure S4, Supporting Information). DOI: 10.1002/smll.201501021 Oil Droplets