Cotton Catches Desert Fog DRINK SAFE WATER

Coated Cotton Catches Desert Fog to Make Safe Drinking Water

This environmental water would be unavailable for drinking without the intelligent use of readily-available materials. It was this adaptive use that inspired researchers at the Eindhoven University of Technology to create a specially coated cotton that can capture moisture from nightly fogs and turn it into perfectly pure drinking water as the sun warms it. 

Under normal conditions, cotton can only absorb 18 percent of its weight in moisture. After applying a polymer to the cotton known as PNIPAAm, the cloth is able to absorb an amazing 340 percent of its own weight in liquid.

The coated cotton is hydrophilic (or absorbent) at lower temperatures, but when it warms up it is hydrophobic – it actually repels water. The fibers on the left are the cotton in a hydrophilic state and those on the right are the cotton in its hydrophobic state.



The water is safe to consume and the polymer-coated cotton stands up to repeated uses. The researchers are now just looking for ways to improve the fabric’s performance – then we may see it used to make moisture-collecting tents or athletic clothing that that keeps sweat away from skin.

Scientists at The Hong Kong Polytechnic University (PolyU) and Eindhoven University of Technology (TU/e) in the Netherlands have developed a special surface modified cotton fabric that absorbs exceptional amounts of water from misty air for up to 340% of its own weight. What makes this coated-cotton so interesting is that the cotton releases the collected water as the temperature rises.

This ground-breaking research was done by Professor John Xin, Head and Chair Professor of PolyU's Institute of Textiles and Clothing (ITC); his PhD graduate Dr Hengrui Yang; and Dr Catarina Esteves at TU/e. The finding has been published on line and will go to print in the scientific journal Advanced Materials (Issue 8, February 2013). 

The scientists grafted a layer of polymer called PNIPAAm to a common cotton fabric. At low temperatures, the cotton modified in this way 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 % of its own weight of water from misty air – compared with only 18% of water from bare cotton.

A further advantage is that the basic material – cotton fabric – is cheap and widely produced. The surface modification with PNIPAAm increases the cost only slightly by 12% which makes the application of the new fabric viable.

The spongy fabric absorbs moisture directly from the air when it is foggy, releasing it as water when the material cools. Every kilogram (two pounds, three ounces) of the fabric produces 7.2 pints of liquid water, and the process is repeatable. 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.

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