Special fog collection mode achieved on an integrative multi-bioinspired hierarchically grooved surface with liquid bridge assistance†

Natural organisms have inspired many recent studies in fog collection. Most materials undergo three sequential steps during fog collection: fog capture, coalescence and transportation. Finally, captured droplets intermittently detach from the surface only when they reach a substantial volume, solely via gravity, which may result in low capture efficiency and surface refresh rate, hindering fog collection efficiency. Herein, inspired by the Namib desert beetle back, Sarracenia trichome, liquid bridges (LBs) in shore birds' beak and the hierarchical structures of natural liquid transportation systems, we design a LB assisted fog collection system (LBAFCS) using hierarchically grooved surfaces (HGSs). The introduction of a LB could not only potentially merge the coalescence and transportation steps in conventional fog collection into a combined removal step, presenting a special fog collection mode, but could also allow droplets to be removed without needing to grow to a larger volume, leading to a higher surface refresh rate. Increasingly hierarchically arranged grooves on the sample surface could significantly increase the removal frequency of droplets, also resulting in a higher surface refresh rate. The results indicate that, compared with a 0 mm LB, a 4 mm length LB can facilitate droplet removal via the hydrophilic regions and grooves on the sample, with a respective 16% and 10% increase in droplet penetration velocity and flux. We achieve a 14.7 kg m⁻² h⁻¹ fog collection efficiency on our 3^rd-groove sample with a 4 mm LB, 2.75 times more than on the same sample without a LB (conventional collection mode), and 1.38 times that with a 0 mm LB.