In arid regions, where water is scarce, fog can sometimes be a hidden source of fresh water. Some communities use "fog harvesters" to collect moisture from the air, typically by using a mesh that captures tiny droplets, which then drip into containers below. Scientists have long been exploring ways to improve the efficiency of these systems, often by combining hydrophilic and hydrophobic materials. Now, a new breakthrough has emerged: a team of researchers has developed a cotton-based material that can switch between being fully hydrophilic and hydrophobic—offering a smart, dynamic approach to water collection.
Dr. Catarina Esteves from Eindhoven University of Technology recently showcased a piece of this innovative "fog cotton." The project was a collaboration between the Eindhoven University of Technology in the Netherlands and Hong Kong Polytechnic University. Starting with regular cotton fabric, the team applied a special coating called PNIPAAm, a temperature-responsive polymer. Normally, untreated cotton absorbs about 18% of its weight in water. But when coated with PNIPAAm, the material's behavior changes dramatically.
At temperatures up to 34°C (93°F), PNIPAAm becomes hydrophilic, allowing the cotton to absorb up to 340% of its own weight in water droplets. However, when the temperature rises further, the polymer undergoes a structural shift, becoming hydrophobic and releasing the collected water as droplets. This unique property makes the material highly efficient and self-releasing, without the need for wind or mechanical shaking, which traditional fog collectors rely on.
The water collected through this method is pure and safe, and the polymer coating can be reused multiple times, making the system both sustainable and cost-effective. Since cotton is inexpensive and PNIPAAm is relatively cheap, this technology has great potential for large-scale applications. Researchers envision using the treated cotton in agricultural settings, where it could absorb moisture at night and release it during the day. It could also be used in tents designed to collect water in dry areas or even in sportswear that manages sweat more effectively.
Currently, the team led by Professor John Xin from Hong Kong Polytechnic University and Dr. Catarina Esteves is working on optimizing the material. Their goal is to enhance the hydrophilic properties of the polymer and lower the temperature at which it switches to hydrophobic mode, making it even more adaptable for real-world conditions. This innovation represents a significant step forward in sustainable water harvesting and could provide a lifeline for communities in water-scarce regions.
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