A serendipitous observation in a Chemical Engineering lab at Penn Engineering (University of Pennsylvania) has led to a surprising discovery: a new class of nanostructured materials that can pull water from the air, collect it in pores and release it onto surfaces without the need for any external energy.
The research, published in Science Advances, was conducted by an interdisciplinary team, including Daeyeon Lee, Professor in Chemical and Biomolecular Engineering (CBE), Baekmin Kim, a postdoctoral scholar in Lee’s lab and first author, Amish Patel, Professor in CBE, and Stefan Guldin, Professor in Complex Soft Matter at the Technical University of Munich (School of Life Sciences).
Water droplets appear on test material
“This work shows how unexpected observations can sometimes open up completely new research directions,” says Stefan Guldin. “The ability of these porous films to extract water from the air and release it in a specific way - without any external energy supply - is not only physically fascinating, but also has enormous application potential: from water supply in arid regions to passive cooling.”
“We weren’t even trying to collect water,” says Daeyeon Lee. “We were working on another project testing the combination of hydrophilic nanopores and hydrophobic polymers when Bharath Venkatesh, a former Ph.D. student in our lab, noticed water droplets appearing on a material we were testing. It didn’t make sense. That’s when we started asking questions.”
Those questions led to an in-depth study of a new type of amphiphilic nanoporous material: one that blends water-loving (hydrophilic) and water-repelling (hydrophobic) components in a unique nanoscale structure. The result is a material that both captures moisture from air and simultaneously pushes that moisture out as droplets.
Water-collecting nanopores
When water condenses on surfaces, it usually requires either a drop in temperature or very high humidity levels. Conventional water harvesting methods rely on these principles, often requiring energy input to chill surfaces or a dense fog to form to collect water passively from humid environments. But this new system works differently.
Instead of cooling, their material relies on capillary condensation, a process where water vapor condenses inside tiny pores even at lower humidity. This is not new. What is new is that in their system, the water doesn't just stay trapped inside the pores, as it usually does in these types of materials.
“In typical nanoporous materials, once the water enters the pores, it stays there,” explains Patel. “But in our material, the water moves, first condensing inside the pores, then emerging onto the surface as droplets. That’s never been seen before in a system like this, and at first we doubted our observations.”
A material that seems to defy physics
Before they understood what was happening, the researchers first thought that water was simply condensing onto the surface of the material due to an artifact of their experimental setup, such as a temperature gradient in the lab. To rule that out, they increased the thickness of the material to see if the amount of water collected on the surface would change.
“If what we were observing was due to surface condensation alone, the thickness of the material wouldn’t change the amount of water present,” explains Lee. But, the total amount of water collected increased as the film’s thickness increased, proving that the water droplets forming on the surface came from inside the material.
Even more surprising: the droplets didn’t evaporate quickly, as thermodynamics would predict. “According to the curvature and size of the droplets, they should have been evaporating,” says Patel. “But they were not; they remained stable for extended periods.” Lee and Patel sent their design off to a collaborator to see if their results were replicable.
“We study porous films under a wide range of conditions, using subtle changes in light polarization to probe complex nanoscale phenomena,” says Stefan Guldin. “But we’ve never seen anything like this. It’s absolutely fascinating and will clearly spark new and exciting research.”
A stabilized cycle of condensation and release
It turns out that they had created a material with just the right balance of water-attracting nanoparticles and water-repelling plastic — polyethylene — to create a nanoparticle film with this special property.
“We accidentally hit the sweet spot,” says Lee. “The droplets are connected to hidden reservoirs in the pores below. These reservoirs are continuously replenished from water vapor in the air, creating a feedback loop made possible by this perfect balance of water-loving and water-repelling materials.”
A platform for passive water harvesting and more
Beyond the physics-defying behavior, the materials’ simplicity is part of what makes them so promising. Made from common polymers and nanoparticles using scalable fabrication methods, these films could be integrated into passive water harvesting devices for arid regions, surfaces for cooling electronics or smart coatings that respond to ambient humidity.
“We’re still uncovering the mechanisms at play,” says Patel. “But the potential is exciting. We’re learning from biology — how cells and proteins manage water in complex environments — and applying that to design better materials.”
The next steps include studying how to optimize the balance of hydrophilic and hydrophobic components, scale the material for real-world use and investigating how to make the collected droplets roll off surfaces efficiently.
Stefan Guldin from the TUM School of Life Sciences says: "Together with our partners at the University of Pennsylvania, we will further develop these novel material concepts. Our aim is to systematically investigate how structure, composition and function can be specifically coordinated at the nanoscale - in order to achieve macroscopic effects that can be used technologically."
Further information
Scientific publication: Science Advances, 21 May 2025, Vol 11, Issue 21. DOI: 10.1126/sciadv.adu8349
Video: Nanopores in action under electron microscope imagery showing water droplets forming and being replenished by stored water in the material itself. – mp4 Video (20 seconds)
This press release has been adapted for TUM School of Life Sciences from the original written by Melissa Pappas at Penn Engineering.