Harvesting water out of thin air, might seem like a pipe dream, but the air-stable water droplet networks, currently being developed by Oak Ridge National Laboratory (ORNL) researchers, could prove to be a step in the right direction. Created with the aid of a new technique, these water droplet networks could also potentially find use in membrane research and biological sensing applications.
Water droplet networks, also known as droplet interface bilayers, consist of numerous water droplets encased within lipid films. Many research efforts are looking into how well networks of these droplets can function as synthetic tissue, electrical circuits or even batteries. Current processes to create these networks can be quite cumbersome, which has curtailed their use.
"The way they’ve been made since their inception is that two water droplets are formed in an oil bath then brought together while they’re submerged in oil," says Pat Collier, a Research Scientist at ORNL, and the study's lead author. "Otherwise they would just pop like soap bubbles."
To create a simpler fabrication process that didn't involve injecting water droplets into an oil bath, the researchers placed the water droplets on a superhydrophobic surface infused with an oil coating.
Superhydrophobic surfaces are very difficult to wet, such as the surface of a lotus leaf. The scientists discovered that the droplets aligned side by side without flowing into each other and that it was possible to create networks without adding lipids into the mix to keep the droplets apart.
"When you have those lipids at the interfaces of the water drops, it’s well known that they won’t coalesce because the interfaces join together and form a stable bilayer," says Jonathan Boreyko, a Postdoctoral Research Associate at ORNL and the study's coauthor. "So our surprise was that even without lipids in the system, the pure water droplets on an oil-infused surface in air still don’t coalesce together."
The water droplets were unexpectedly prevented from merging by the presence of a thin oil film squeezed between the droplets, thanks to the oil-infused surface. Being able to more effectively control the behavior of water droplets on such surfaces could yield greater insights into creating viable fog-harvesting technologies, the researchers claim.
Additionally, adding lipids to create more membrane-like water droplet networks could open up the way to their use in synthetic biology and bio-sensing applications, the team says. "For example, we could make a bio-battery or a signaling network by stringing some of these droplets together," explains Collier. "Or, we could use it to sense the presence of airborne molecules."
Their research was recently published in the Proceedings of the National Academy of Sciences.
The video below shows how the oil film prevents the droplets from merging.