Researchers from the Beijing Institute of Graphic Communication and Beihang University have developed a two-stranded thread designed to harvest water from fog. The work, published in Polymer Science, shows a yarn capable of catching tiny droplets from humid air and guiding them toward collection. The study underscores that this performance emerges from a careful blend of surface properties and fiber geometry, offering a practical approach to fog water harvesting for communities in arid regions and for remote locations across North America. The researchers highlight that the key lies in the deliberate pairing of hydrophobic and hydrophilic characteristics within a single thread, rather than relying on a single material or passive action.
Inspiration for the design comes from nature’s patterns. Desert insect shells and other natural surfaces exhibit alternating hydrophobic and hydrophilic regions that manage water contact, while spider silk demonstrates an inherent ability to shuttle moisture along fibers. By translating these cues into a synthetic thread, the team crafted a scaffold where surface chemistry nudges droplets to form and then steers them toward transport channels, creating a continuous water pathway along the length of the fiber.
The yarn’s composition blends two nanofiber components. The outer network is built from water-repellent PVDF-HFP, while hydrophilic PAN nanofibers form an interconnected moisture-transport layer. This combination balances efficient droplet capture with rapid guidance toward a collection point, enabling sustained fog harvesting under fluctuating environmental humidity. The choice of PVDF-HFP and PAN provides a synergistic effect that maximizes both water uptake and controlled transport.
Fabrication used electrospinning to generate ultra-fine PAN and PVDF-HFP fibers, followed by a twisting step that establishes alternating hydrophobic and hydrophilic segments along the thread. This configuration mirrors nature’s dual strategy: the hydrophobic zones grab water droplets from the fog, and the hydrophilic zones deliver them to the transport pathways. The resulting yarn behaves like a compact fog-harvesting unit, guiding moisture from the air into a usable reservoir with minimal energy input.
Mechanistically, hydrophobic segments encourage rapid droplet nucleation, while hydrophilic sections enable swift transport and coalescence. The interaction reduces the delay between capture and collection, increasing overall water throughput compared with single-chemistry fibers. The alternating pattern creates a microfluidic network at the fiber scale, turning scattered fog droplets into a steady stream of liquid that can be harvested efficiently.
In controlled fog environments, tests showed notable gains in water collection efficiency compared with conventional homogeneous filaments. The two-stranded yarn outperformed single-material fibers by taking advantage of the synergy between capture and transport, yielding more water per unit area under identical fog conditions. Experts say this combination taps into the best of both worlds, offering a robust passive fog-harvesting strategy that could function in varied climates across North America, including coastal regions and higher elevations in Canada and the United States.
Earlier efforts in this field included cooling and water collection systems that operate without electricity. The new two-stranded approach adds a flexible, scalable option based on surface chemistry and fiber architecture rather than external power. By integrating hydrophobic capture with hydrophilic transport on a single thread, this technology holds promise for portable, low-energy fog-harvesting devices, outdoor shelters, and water supply solutions in remote locales. Future work will explore optimizing fiber ratios, scaling production, and testing under diverse fog regimes to better understand performance in real-world Canadian and American environments.