Microbubble-Mediated Synthesis of Smart Spindle Microfibers for Fog Harvesting

Fog has significant potential as a water resource, offering a solution for alleviating the global risk of freshwater scarcity. Spindle-knotted microfibers are highly effective for fog collection, though the complexity of fabricating such structures remains a significant challenge. In this study, a simple microfluidic method using microbubbles is introduced for the fabrication of smart spindle microfibers (SSMs). The combination of microbubbles of varying sizes, induced by pulses from a peristaltic pump, and thermo-responsive poly(N-isopropylacrylamide) (PNIPAm)-based materials facilitated the formation of periodic knots and joint structures with enhanced structural stability and hydrophilic rough surfaces. The spindle-knotted structure, featuring textured hydrophilic surfaces, extends the three-phase contact line and maximizes the volume of the collected water droplets. This promotes the rapid detachment of large droplets formed within a short time, thereby enhancing fog harvesting efficiency. This approach achieves a collection rate of 0.046 g min⁻¹, representing 161% of the previously reported fog collection efficiency. Moreover, SSMs adjust their wettability across different temperature cycles owing to the thermo-responsive properties of PNIPAm, ensuring consistent and reliable fog collection efficiency, even under changing environmental conditions. This adaptability provides practical insights that enable efficient large-scale water harvesting, addressing the urgent need for effective water collection solutions.