-- Microscopic cones on an underwater surface trapped a rising bubble in 1.5 milliseconds in a laboratory test recorded with a Revealer X190 high-speed camera. On a flat surface with the same nanoparticle coating, the bubble bounced repeatedly and took 71.5 milliseconds to be captured.
In a 2025 study in Nature Communications, Yue Hu of Shanghai Jiao Tong University and colleagues paired the high-speed images with particle image velocimetry (PIV), a method for tracking fluid motion. They investigated how the cones change the way water drains from the gap between a rising bubble and the gas held on the surface.
A composite from a 2025 study shows the cone array at left and high-speed images and trajectories of rising bubbles at right. In the sequence shown, the bubble on the flat surface rebounds before capture, while the bubble on the cone-covered surface joins the trapped gas on its first approach.
The team mounted both test surfaces upside down in deionized water and released bubbles from below. The cones in the main comparison stood 600 micrometers tall, with their centers 1 millimeter apart. The high-speed camera recorded 9,000 frames per second to track each bubble as it approached the surface and either bounced or joined the gas held there.
A bubble approaching the surface squeezes water between itself and the trapped gas. That film must drain and rupture before the bubble can merge with the gas layer. The researchers found that the cones held the line where gas, water and solid meet in place while allowing the interface between the gas and water to deform.
For the PIV measurements, the team illuminated tiny tracer particles with a sheet of laser light and recorded them with the Revealer high-speed camera X190 at 4,000 frames per second. The PIV velocity maps showed water moving outward from the gap. The flow around the bubble formed stronger vortices with taller cones relative to their base radius. Separate observations tracked changes in the shape of the gas layer, and a model predicted that the water film could thin faster near the bubble’s edge.
Where the bubble approached also mattered. The researchers moved the test surface sideways in steps of 200 micrometers. In that experiment, capture took about 100 milliseconds near the middle of a unit in the array and about 1.5 milliseconds near the line held in place by the cones.
Cone proportions set a limit. In some tests, when the cones were more than 7.8 times as tall as their base radius, bubbles remained suspended at the array without reaching the trapped gas. The researchers used the high-speed camera footage to classify which bubbles bounced, merged or stayed suspended.
The team also tested the surfaces in flowing water. Images taken at 200 frames per second showed a continuous gas channel along the cone-covered surface and scattered bubbles along the flat one. Volume measurements showed that the array collected 98.8% of the injected gas in a 12-hour test at one flow setting. At a higher flow setting, its collection efficiency fell to about 50%.
The work could inform the design of surfaces for separating gas from water. The tests show why designers need to consider both where a bubble meets the surface and whether the resulting gas channel can hold up under flow.
Read the study in Nature Communications.
Understanding ultrafast free-rising bubble capturing on nano/micro-structured super-aerophilic surfaces. *Nature Communications* 16, 3682 (2025). https://doi.org/10.1038/s41467-025-59049-x
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