Atmospheric water harvesting, a crucial method for mitigating water scarcity, relies heavily on the condensation of water vapor from the air. This process, however, faces challenges due to the uncontrollable growth of condensed droplets leading to surface flooding. The Tsinghua team has addressed this issue by creating an engineered pattern on glass using hydrogel fibers.
The team's inspiration stemmed from the thorny devil lizard, which efficiently spreads water from its scales to its mouth via capillary channels. Similarly, the catfish's epidermal mucus layer, known for reducing swimming drag, offered insights into low-drag droplet shedding. Combining these natural strategies, the researchers designed hydrogel fibers composed of sodium alginate and polyvinyl alcohol. These fibers feature a partially polymerized surface with an arch structure, adorned with branched -OH and -COOH chains that exhibit a strong affinity for water molecules.
This affinity is crucial for the hydrogel's function. As Prof. Qu explains, "The hydrogel pattern functions similarly to the directional water dispersion over the integuments of lizards." The pattern enables droplets formed on the glass to be swiftly moved to the hydrogel fiber, effectively regenerating the condensing sites. This results in a reduction of over 40% in the energy of the droplet-condensing surface system, providing the necessary driving force for efficient water harvesting.
The researchers employed fluorescent molecules as probes to observe the droplet movement, revealing a layered sliding behavior on the hydrogel surface. Dr. Ji elucidates, "The dangling chains over the hydrogel surface act like the mucus layer of the catfish, lubricating the friction between the droplets and the condensing surface." This bioinspired design allows for a significant increase in the condensation rate by 85.9%, without the need for external energy input.
Furthermore, the hydrogel pattern has been successfully applied to enhance the water collection rate of solar evaporative water purification systems by 109%. This remarkable achievement not only demonstrates the practical application of the technology but also sheds light on the potential of bioinspired designs in addressing environmental challenges.
Research Report:Pumping and sliding of droplets steered by a hydrogel pattern for atmospheric water harvesting
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