Microtextured coatings from superhydrophobic bark-derived bioparticles for fog harvesting

Abstract

We have developed bioparticle-based hybrid superhydrophobic–hydrophilic coatings that significantly enhance water collection in fog harvesting. The use of superhydrophobic betulin crystals, extracted from birch bark, to create microtextured coatings represents a sustainable and superior alternative to synthetic nano/micro patterning. These betulin coatings effectively accelerate condensation and coalescence of water microdroplets, leading to considerable drop growth and water collection. The surface energy heterogeneity, with a hydrophilic substrate surrounding the superhydrophobic bioparticles, creates a surface free energy gradient that substantially enhances droplet mobility. Notably, we observed a non-monotonic increase in condensation and water collection rates with surface particle density. Through rigorous testing on both permeable and impermeable substrates, we found that the water collection efficiency of betulin-coated surfaces far surpasses that of bare substrates. Further, the betulin-based collectors increased the efficiency of widely-used fog harvesters like Raschel meshes by up to 275%. Compared to previously reported biomimetic microtextured surfaces, our betulin-based collectors demonstrate unparalleled water harvesting capabilities, signaling a breakthrough in environmentally friendly patterning for water condensation and harvesting.