Hierarchically Branched Siloxane Brushes for Efficient Harvesting of Atmospheric Water

Abstract

AbstractAtmospheric water harvesting is considered a viable source of freshwater to alleviate water scarcity in an arid climate. Water condensation tends to be more efficient on superhydrophobic surfaces as the spontaneous coalescence‐induced droplet jumping on superhydrophobic surfaces enables faster condensate removal. However, poor water nucleation on these surfaces leads to meager water harvest. A conventional approach to the problem is to fabricate micro‐ and nanoscale biphilic structures. Nonetheless, the process is complex, expensive, and difficult to scale. Here, the authors present an inexpensive and scalable method based on manipulating the water‐repellent coatings of superhydrophobic surfaces. Flexible siloxane can facilitate water nucleation, while a branched structure promotes efficient droplet jumping. Moreover, ToF‐SIMS analysis indicated that branched siloxane provides a better water‐repellent coating coverage than linear siloxane and the siloxanes comprise hydrophilic and hydrophobic molecular segments. Thus, the as‐prepared superhydrophobic surface, TiO2 nanorods coated with branched siloxanes harvested eight times more water than a typical fluoroalkylsilane (FAS)‐coated surface under a low 30% relative humidity and performed better than most reported biphasic materials.