Directional Self-Transportation of Droplets on Superwetting Wedge-Shaped Surface in Air and Underliquid Environments

Abstract

The directional self-transportation of droplets has aroused great attention in microfluidic systems. However, most reported surfaces are mainly designed for driving water droplets to move in air, displaying low adaptability in complex environments. This work presents a wedge-shaped surface with multiple superwettability, i.e., superhydrophilicity/superoleophilicity and underwater superoleophobicity/underoil superhydrophobicity, fabricated by electrodeposition of a metal–organic framework on a copper sheet. This surface exhibited excellent performance for driving droplet self-transportation, regardless of the droplet type (water or oil) and environmental media (air or underliquids). In air, the wedge-shaped surface with wedge angle of 9.2° could move droplets of water and dodecane up to 24.5 mm and 17.9 mm, respectively. The movement of water droplet under dodecane, however, dropped from 24.5 mm to 22.1 mm, while the dodecane droplet underwater increased from 17.9 mm to 20.3 mm in moving displacement, indicating the underliquid environment is in favor of manipulation of oil droplets. Furthermore, the droplet convergence, transportation, and separation were achieved on the well-designed multiple wedge tracks in air with a total movement distance up to 60.0 mm. The test of micro-oil droplets collecting under water demonstrated that a sponge with two wedges has 2.1 times the oil droplet collection capacity over that of the sponge only, providing a new strategy for efficient treatment of the micro-oil droplets contaminated water.

Quantitative liquid storage by billiards‐like droplet collision on surfaces with patterned wettability

“…However, there remains a dearth of research on the dynamic storage of droplets. It is well known that stationary droplets can acquire kinetic energy through wedge‐shaped patterns in the absence of external fields, a motion induced by asymmetric Laplace pressure 37,38 . In comparison to three‐dimensional (3D) fully superhydrophobic structures, composite wetting wedges on a two‐dimensional plane enable droplets to attain greater velocities 39,40 .…”

Studying Liquid-Infused Surfaces with Affordable Surface Features Infiltrated with Various Lubricants from Corrosion, Biofouling, and Fluid Drag Viewpoints

“…These surfaces possess relatively low contact angle hysteresis, albeit their low contact angle . Besides drag reduction, these surfaces could be utilized in many applications, such as anti-icing, droplet manipulation, , food packaging, and dropwise condensation. , Furthermore, these surfaces have found their way into the industry. − …”

Liquid-Assisted Bionic Conical Needle for In-Air and In-Oil–Water Droplet Ultrafast Unidirectional Transportation and Efficient Fog Harvesting

“…In recent years, research on directional self-transportation of tiny droplets has received widespread attention due to its significant applications such as microfluidics, fog collection, droplet manipulation, and so forth. − In nature, some organisms can collect tiny droplets in the air after hundreds of millions of years of evolution. − For instance, cacti enable the spontaneous transport of tiny droplets from the tip to the base of their spines. − Spider silk can effectively condense and transport minuscule water droplets in mist due to its periodic spindle-knot structure. , The surface of pitcher plants exhibits continuous directional droplet transport along radial ridges, representing unique lubrication properties. − Besides, cacti can survive in extremely arid desert environments because they can collect water from fog. When the micro water droplets come in contact with the surface of the conical microspines, they will automatically move from the tip to the base of conical microspines under the action of the Laplace pressure generated from the curvature gradient surface. − …”