Directional Transport of Underwater Bubbles on Solid Substrates: Principles and Applications

Abstract

The manipulation of underwater bubbles on substrates has received extensive research interest from both the scientific community and industry, including the chemical industry, machinery, biology, medicine, and other fields. Recent advances in “smart” substrates have enabled the bubbles to be transported on demand. Herein, the progress in the directional transport of underwater bubbles on various types of substrates is summarized, including planes, wires, and cones. The transport mechanism can be classified as buoyancy-driven, Laplace-pressure-difference-driven, and external-force-driven according to the driven force of the bubble. Moreover, the wide applications of directional bubble transport are reported, ranging from gas collection, microbubble reaction, bubble detection and classification, bubble switch, and bubble microrobots. Lastly, the advantages and challenges of various directional bubble transportation methods are discussed, and the current challenges and future prospects in this field are also discussed. This Review outlines the fundamental mechanisms of underwater bubble transportation on solid substrates and helps to understand the methods of optimizing bubble transportation performances.

Bubble Engineering on Micro-/Nanostructured Electrodes for Water Splitting

“…112−116 Thus, the effective bubble transportation becomes vital for gas collection and can reduce the cost and energy during gas separation. 117 From the aspect of electrode engineering, utilizing Laplace pressure differences generated by wettability gradients or curvature shapes is the most common way to drive the directional movement of bubbles. 117−119 Inspired by the natural strategy of fluid manipulation, Cao et al realized the spontaneous separation of hydrogen and oxygen via self-driven bubble manipulation on bioinspired electrode in water splitting.…”

“…High purity of the gaseous production is the premise of downstream transportation and industrial applications. Compared with technologies using membrane-based systems (e.g., proton-exchange membrane (PEM) and anion-exchange membrane (AEM)), − membrane-less electrolysis can accommodate the operation at any pH, reduce the complexity by eliminating separation membranes, and increase the ionic mobility, attracting tremendous attention recently. − Thus, the effective bubble transportation becomes vital for gas collection and can reduce the cost and energy during gas separation . From the aspect of electrode engineering, utilizing Laplace pressure differences generated by wettability gradients or curvature shapes is the most common way to drive the directional movement of bubbles. − …”

Underwater Bubble Manipulation on Surfaces with Patterned Regions with Infused Lubricants

“…The thin oil layer eliminates the pinning effect of the solid substrate on the bubble, thus allowing the bubble to slide at a small angle of inclination. 14 As a result, the bubbles can move faster on the slippery lubricant-infused surface (LIS). The LISs with low sliding resistance and high resistance to pressure and moisture are considered to be ideal for the optimization of current bubble manipulation systems.…”

Self‐Driving Underwater “Aerofluidics”

“…The transportation and manipulation of trace gases is a technology with great potential since many chemical reactions, analyses, and detection objects involve gases. [10][11][12][13] Spontaneous transport of bubbles underwater has been widely realized through topographic modulation of surface wetting gradients (such as superhydrophobic cones, [14,15] superhydrophobic wedge-shaped structures, [16] lubricated slippery cones, [17] and slippery wedge-shaped structures [18,19] ) that break the asymmetric contact line. However, gas transport based on these strategies is limited by short transport distances due to the fundamental tradeoff of hydrodynamics, and gases can only be manipulated macroscopically as a whole.…”