Penn engineers develop energy-free material that captures and releases water from air

Led by Daeyeon Lee and Amish Patel, professors in Chemical and Biomolecular Engineering, along with postdoctoral scholar Baekmin Kim and collaborator Stefan Guldin from the Technical University of Munich, the team identified a unique amphiphilic nanoporous structure. This composition blends water-attracting and water-repelling elements, enabling it to both capture airborne moisture and release it as surface droplets-without requiring energy input or extreme humidity.

The material works through capillary condensation, drawing water vapor into nanopores even at modest humidity levels. Unlike conventional porous materials, where moisture remains trapped, this film moves the water to its surface. "In typical nanoporous materials, once the water enters the pores, it stays there," said Patel. "But in our material, the water moves...then emerging onto the surface as droplets."

To validate their findings, the team ruled out surface condensation by increasing the film's thickness. More water collected as the film grew thicker, confirming internal capillary activity. Even more curious, the droplets resisted evaporation, defying thermodynamic expectations. "They remained stable for extended periods," noted Patel.

Guldin, who tested the material independently, confirmed the anomaly. "We've never seen anything like this. It's absolutely fascinating and will clearly spark new and exciting research."

The film's performance hinges on a delicate balance between hydrophilic nanoparticles and polyethylene. "We accidentally hit the sweet spot," Lee explained. The internal reservoirs formed by the nanopores replenish themselves, supporting a stable, ongoing cycle of moisture uptake and droplet release.

These films, composed of inexpensive materials using scalable methods, hold promise for practical uses-from passive water harvesters in dry environments to cooling surfaces for electronics and responsive smart coatings. "We're still uncovering the mechanisms at play," said Patel. "But the potential is exciting."

The team plans to refine the hydrophilic-hydrophobic balance, enhance scalability, and improve droplet release efficiency, with an eye toward sustainable water and cooling solutions using only ambient air moisture.

Research Report:Amphiphilic nanopores that condense undersaturated water vapor and exude water droplets