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Bubbles have been extensively explored as energy carriers ranging from boiling heat transfer and targeted cancer diagnosis. Yet, despite notable progress, the kinetic energy inherent in small bubbles remains difficult to harvest. Here, we develop a transistor-inspired bubble energy generator for directly and efficiently harvesting energy from small bubbles. The key points lie in designing dielectric surface with high-density electric charges and tailored surface wettability as well as transistor-inspired electrode configuration. The synergy between these features facilitates fast bubble spreading and subsequent departure, transforms the initial liquid/solid interface into gas/solid interface under the gating of bubble, and yields an output at least one order of magnitude higher than existing studies. We also show that the output can be further enhanced through rapid bubble collapse at the air/liquid interface and multiple bubbles synchronization. We envision that our design will pave the way for small bubble-based energy harvesting in liquid media.

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There remain significant gaps in our ability to predict dewetting and wetting despite the extensive study over the past century. An important reason is the absence of nanoscopic knowledge about the processes near the moving contact line. This experimental study for the first time obtained the liquid morphology within 10 nm of the contact line, which was receding at low speed (U < 50 nm/s). The results put an end to long-standing debate about the microscopic contact angle, which turned out to be varying with the speed as opposed to the constant-angle assumption that has been frequently employed in modeling. Moreover, a residual film of nanometer thickness ubiquitously remained on the solid after the receding contact line passed. This microscopic residual film modified the solid surface and thus made dewetting far from a simple reverse of wetting. A complete scenario for dewetting and coating is provided.

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The air micro-and nanobubbles on a silicon wafer surface, generated by ethanol−water exchange method in THF solution, are found with anomalous small contact angles on the gas side due to the pinning effect. As the pinning effect is only with the limited region of a bubble and varies with bubble size, the difference in contact angle between the microbubbles and nanobubbles is recognized. With a high-resolution atomic force microscopy, in situ direct observations of THF hydrate nucleation are performed in the presence of air micro-and nanobubbles in solution. On the basis of the observations, the sizes of the hydrate crystallites along the bubble edge are much larger than those in nonbubble regions, which can be explained by the lower nucleation barrier at the contact line region as to the classical nucleation theory. The growth of hydrate crystals at the bubble contact line experiences the competition for THF molecules, probably through Oswald ripening process, resulting in the spaced distribution of THF hydrate crystallites along the bubble edge.