Enhanced Liquid Transport on a Highly Scalable, Cost-Effective, and Flexible 3D Topological Liquid Capillary Diode

Abstract

Directional liquid-transport surfaces have various applications, such as, open microfluidic devices, fog collection, oil-water separation, and surface lubrication. However, current liquid-transport surfaces are expensive, complicated to manufacture, and lack scalability. Moreover, they exhibit low transport speeds and distances. In this study, a laser cutter is used to fabricate scalable, low-cost unidirectional liquid-transporting surfaces with enhanced transport speed and distance using polymeric materials. Cutting and engraving methods are used to create a liquid capillary diode comprising 3D wedge shapes, thereby obtaining an appropriate pressure gradient and liquid pinning. The developed liquid capillary diode exhibits the fastest transport speed (3-17.7 mm s(-1)) reported so far, and a large normalized distance (L/R: transport distance/radius of dispensed droplet). The transport distance increases with the square root of time under various contact angles and liquid viscosities, which agree well with the theoretical scaling results obtained using the modified Washburn model. Additionally, the flexible liquid capillary diode operates adequately even when bent with the maximum curvature of 0.1 mm(-1). The results provide better design guidelines for 3D topological liquid-transport surfaces for various applications.