Influence of geometric patterns of microstructured superhydrophobic surfaces on water harvesting performance via dewing

Abstract

We investigate how the wetting state of microstructured SHPo surfaces influences water harvesting performance via dewing by testing two different patterns including posts and grates with varying structural parameters. On grates, the observed Cassie wetting state during condensation is well described by the thermodynamic energy criteria, and small condensates can be efficiently detached from the surfaces due to the small contact line pinning force of Cassie droplets. Meanwhile, on posts, the observed wetting state is dominantly the Wenzel state regardless of the thermodynamic energy of each state, and the condensates are shed only after they grow to a sufficiently large size to overcome much larger pinning force of the Wenzel state. Based on mechanical force balance model and energy barrier consideration, we attribute the difference in the droplet shedding characteristics to the different dynamic pathway from the Wenzel state to the Cassie state between posts and grates. Overall, the faster droplet shedding helps enhance the water harvesting performance of the SHPo surfaces by facilitating the condensation on the droplet-free area, as evidenced by the best water harvesting performance of grates on the Cassie state amongst the tested surfaces.