The cotton is coated with a polymer known as PNIPAAm, which allows it to absorb 340% of its weight in fog droplets.
‘Fog harvesting’ for water isn’t a new technique. People use netting to capture fog droplets, which are then collected in a container. The process is hardly efficient, but thanks to a special treatment for cotton, it may become a viable solution for obtaining water in desert regions.
Researchers from the Eindhoven University of Technology and the Hong Kong Polytechnic University have developed a coating that allows the cotton to absorb high amounts of water from misty air. The cotton is treated with a polymer known as PNIPAAm, which allows it to absorb 340% of its weight, compared to only 18% without the coating. It has a sponge-like structure at temperatures up to 34°c and is highly hydrophilic.
As it gets warmer, the cotton releases the collected water by itself as it becomes hydrophobic (water-repellant). The research has shown that this cycle can be repeated many times.
The inspiration for this new coated cotton comes from nature, as there are certain beetles and spiders that can capture water droplets on their bodies or webs. According to the researchers, the cotton fabric is cheap and easily produced and the polymer is also inexpensive. Applications could include cotton fibers laid on cultivated soil to provide water directly, camping tents that collect water at night, and sportswear that keeps athletes dry when sweating.
The team now plans to optimize the quality of the coated cotton, increase the amount of water that can be absorbed, and lower the temperature at which it changes from its absorbing to its releasing state.