  Numerous natural and engineering scenarios necessitate entrapment of air
pockets or bubbles on submerged surfaces, e.g., aquatic insects, smartphones,
and membranes for separation and purification. Current technologies for bubble
entrapment rely heavily on perfluorocarbon coatings, which limits their
sustainability and applications. Here, we investigate doubly reentrant
cavities, a biomimetic microtexture capable of entrapping air under wetting
liquids, under static and dynamic pressure cycling. The effects of positive,
negative, and positive-negative cycles are studied across a range of pressure
amplitudes, ramp rates, intercycle intervals, and water column heights.
Remarkably, the fate of the trapped air under pressure cycling falls into the
following three distinct regimes: the bubble (i) monotonically depletes, (ii)
remains indefinitely stable, or (iii) starts growing. This hitherto unrealized
richness of underwater bubble dynamics will guide the development of
coating-free underwater technologies and provide clues into the curious lives
of air-breather aquatic/marine insects.
