Bioinspired Tip-Guidance Liquid Jetting and Droplet Emission at a Rotary Disk via a Surface Energy Gradient

Effective droplet emission is of fundamental importance for practical application, such as agricultural sprays to painting, atomization, emulsification, and catalytic action. Highly viscous liquids are commonly used, such as printing inks, which hinder the ejection at the nozzle. A big challenge faced by people is how to obtain stable and controllable liquid droplets in a wide range of viscosities. Inspired by the rotation shaking of droplets on fiber clusters and the rotary spraying disk technique, here, we demonstrate uniform microdroplet (1-2000 mPa·s) generation in a tip-guided way that replaces the commonly confined nozzle by a double-layer spinning "sandwich" multitip disk (SSMD). A surface energy gradient induced by the margin structure of the alternating gas wedge and solid tip guides liquid to move along the solid tip, which is ejected at the end of the tip, forming a ring of droplet clusters. SSMD improves the effective droplet-jet process to 7/10 of the whole drainage process and enhances the efficiency with a production drop volume of ∼3.19 × 10⁷ μL/h and production droplet numbers of ∼3.3 × 10⁴ per second. Droplets can be fine-tuned between 0.1 and 1.0 mm via the tip structure, liquid property, and spinning angular velocity with a narrow size distribution. This facile tip-guided design could inspire the possibility of energy-efficient droplet production techniques in various fluid applications, such as spraying and printing. It may further improve other fluid systems that serve as a crucial component for high-speed droplet manipulation, liquid transport, and water vapor capturing.