In rain-starved regions, fog catchers can provide much needed water for drinking or crops. A new material makes that process more efficient with a corrugated, lubricated surface that builds up larger droplets that slide off easily to be collected.
Water-harvesting materials usually come with a trade-off: they either trap droplets well, or help them travel into a reservoir efficiently. It鈥檚 tricky to do both because the material must be sticky to grab droplets, but slippery enough to let the water slide off into a receptacle. Most current set-ups use vertical hydrophobic surfaces to harvest water. If fog encounters these surfaces, some droplets 鈥� but not many 鈥� will condense there and gravity will pull them into a basin.
at the University of Texas at Dallas聽and at Pennsylvania State University, led a team that designed a material that is 200 per cent more efficient. The specialised surface is hydrophilic, so it chemically bonds with water molecules to collect more drops.
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Tiny water slides
To make it, they carved grooves 20 micrometres deep and 50 micrometres wide into silicon to give water molecules more surface area to latch on. Then, they etched the surface with nanoscale bumps and deposited a layer of a compound called silane on top. Finally, they added a thin layer of hydrophilic lubricant that grips onto the rough nanotexture.
Because the lubricant is a liquid and its molecules are always moving, no permanent bonds are formed with the water, like they would be if it were a hydrophilic solid. So, droplets are trapped on the surface but can still move around to coalesce into larger drops and be collected.
The researchers tested their material in a room with a commercial humidifier running for two weeks. They found that a square metre of it could collect more than 100 litres of water per day. 鈥淔or typical fog-harvesting mats that people use in remote areas, they can only collect around 1 to 10 litres of water per square metre per day. This is way better,鈥� says Wong.
Plus, Dai says, it鈥檚 cheap and easy to make. He says this material could make power plants more efficient, because they expend a lot of energy harvesting steam.
Science Advances
Read more: Desert plant seen drinking fog and mist with its leaves
