Bubbles that should rise instead accelerate downward when they merge.

In clean energy devices like water electrolyzers, gas bubbles form on solid surfaces. Usually, buoyancybuoyancyThe upward force that makes bubbles rise due to being lighter than the surrounding fluid. makes bubbles float up and away. But at high gas production rates, bubbles stay trapped near the surface, blocking energy transfer. Researchers studied why this happens using high-speed cameras around microelectrodes. They found that a rising bubble merges with a smaller bubble still stuck to the surface. When these unequal bubbles join, the merging surface pulls unevenly. This mismatch creates fluid forces that push the bubble downward instead of upward. The bubble reverses direction and speeds toward the surface at almost two orders of magnitude above its rising speed. Repeated mergers create a steady downward force that easily overcomes buoyancy, trapping the bubbles.

Why it matters

This affects clean energy technologies like water electrolysis and boiling systems, where trapped bubbles reduce efficiency and increase energy costs. Understanding this mechanism could help design better devices for energy generation and thermal management.

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