Researchers from Eindhoven University of Technology, The Netherlands, and Hong Kong Polytechnic University, China, turned a cotton fabric into water-collecting material by applying a coating of PNIPAAm, a polymer, to the cotton fabric. At lower temperatures, this cotton has a sponge-like structure at microscopic level. Up to a temperature of 34°C it is highly hydrophilic, in other words it absorbs water strongly. Through this property the cotton can absorb 340 percent of its own weight of water from misty air, compared with only 18 percent without the PNIPAAm coating.
In contrast, once the temperature raises the material becomes hydrophobic or water repellant, and above 34°C the structure of the PNIPAAm-coated cotton is completely closed. When these high temperatures are reached the cotton has released all the absorbed water, which is totally pure. The research shows that this cycle can be repeated many times.
Beetles in desert areas can collect and drink water from fogs, by capturing water droplets on their bodies, which roll into their mouths. Similarly, some spiders capture humidity on their silk network. This was the inspiration for this new coated-cotton material, which collects and releases water from misty environments simply as the temperature changes throughout the day.
This material could be used as a component of free-standing water-collecting devices for deserts and dry mountain regions, and as additives for agricultural soils in drought-prone areas. Work continues on tuning the temperature at which water condenses from the material in hopes of developing it on a commercial scale.
The research was led by John Xin at PolyU and Dr. Catarina Esteves at TU/e. They intend to investigate further how they can optimize the quality of the new material. For example, they hope to increase the amount of water absorbed by the coated-cotton. Moreover they also expect to be able to adjust the temperature at which the material changes from water-collecting to the water-releasing state, towards lower temperatures.