A study published in Science Advances highlights a new material that could pave the way for innovative methods of harvesting water from the air in arid regions and for cooling devices or buildings through evaporation.
“We weren’t even trying to collect water. We were working on a different project testing a combination of hydrophilic nanopores and hydrophobic polymers when Bharath Venkatesh, a former doctoral student in our lab, observed the formation of water droplets on a material we were testing. It didn’t make sense. That’s when we started questioning,” explained Daeyeon Lee, a professor of chemical and molecular engineering at the University of Pennsylvania, USA.
This curiosity led the scientists to an in-depth exploration of a new type of amphiphilic nanoporous material, which combines hydrophilic and hydrophobic components in a unique nanostructure.
The outcome is a material capable of capturing moisture from the air and simultaneously expelling it in droplet form.
Typically, water condensation on surfaces requires either a drop in temperature or very high humidity levels. Conventional water collection methods rely on these principles and often require energy input to cool surfaces or create dense fog for passive water collection in humid environments.
However, Lee and Patel’s system operates differently. Instead of cooling, their material utilizes capillary condensation, a process in which water vapor condenses inside small pores even at low humidity levels. While this concept isn’t new, their system prevents water from being trapped within the pores, contrary to what normally occurs with similar materials.
Initially, researchers suspected that water merely condensed on the material’s surface as an artifact of their experimental setup, possibly due to a temperature gradient in the lab. To verify this, they increased the material’s thickness to check if it influenced the amount of water accumulated on the surface.
“If what we observed was merely due to surface condensation, the material’s thickness wouldn’t change the amount of water present,” Lee explained.
Nevertheless, as the thickness increased, so did the total water collection, indicating that surface water droplets originated from within the material.
Moreover, the “droplets did not evaporate quickly, as thermodynamics would predict, but remained stable for extended periods.”
The team devised a material merging the perfect balance of water-attracting nanoparticles and water-repellent plastic (polyethylene) to form a nanoparticle film with this special property.
“We found the perfect solution,” affirmed Lee. The droplets are connected to hidden reservoirs within the pores below, which are continually replenished with water vapor from the air, establishing a feedback loop due to this ideal balance between hydrophilic and hydrophobic materials.
Constructed from common polymers and nanoparticles using scalable manufacturing methods, these films could be integrated into passive water collection devices for arid areas, cooling surfaces for electronic devices, or smart coatings that respond to ambient humidity.
