Ladderlike Conical Micropillars Facilitating Underwater Gas-Bubble Manipulation in an Aqueous Environment

Underwater gas-bubble manipulation in aqueous environments is of great importance in industry and academia. Although the underwater gas bubble has been proved to be directionally transportable by various structures, transporting gas bubbles in 3D space remains a challenge. In this research, two kinds of tapered pillars, that is, ladderlike and helical ladderlike, were proposed for manipulating gas bubbles. To fabricate such unique structures, an improved alternative coating and etching method was developed. To meet the requirements of underwater gas-bubble transport, a modified gas-bubble slippery technology was also developed to enhance the aerophilic ability. The dynamics of the gas bubble was analyzed using a high-speed camera. The Laplace force that resulted from the geometry gradient was found to play a significant role in tuning the gas-bubble velocity. Through adjustments on the wettability, tilt angle, and geometry of each section of the tapered pillar, tuning the transport velocity from 113.9 ± 10.3 to 309.1 ± 5.8 mm/s becomes possible. On the basis of these findings, the helical ladderlike tapered pillar was fabricated and demonstrated to be able to transport gas bubbles in 3D space. These results may provide a new and systematic way to design and fabricate materials and structures for directional gas-bubble transport in 3D space.