Specially-treated cotton nonwovens have been employed to capture significant amounts of water from desert fog.

A research team from the Technical University of Eindhoven in the Netherlands and Hong Kong Polytechnic University have discovered that coating the cotton fabric with temperature responsive PNIPAAm (Poly(N-isopropylacrylamide) polymer equips the material to absorb up to 340 times its own weight of water from misty air. And significantly, the material releases the collected water naturally as it gets warmer.

This property suggests it could provide a potential solution to providing water to desert regions, for example for agricultural purposes.

At lower temperatures, the material has a sponge-like structure at microscopic level and up to a temperature of 34°C is highly hydrophilic. As a result it can absorb 340 % of its own weight of water from misty air – compared with only 18% without the coating.

Once the temperature rises, 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 the new material.
Eindhoven researcher Dr Catarina Esteves a further advantage is that the basic material is cheap and can be easily and locally produced. The polymer coating increases the cost by about about 12%.

Fine-mesh ‘fog harvesting nets’ are already being used in some mountains and dry coastal areas, but these operate on a different principle,collecting water from misty air in droplets that gradually form on the nets and fall to the ground or a suitable receptacle. This system, however, depends on a strong air flow. The new material can also work without wind and can be laid directly where the water is needed, for example on cultivated soil. The researchers are also considering completely different applications such as camping tents that collect water at night, or sportswear that keeps athletes dry.

Pic: TripAdvisor