Biological inspired particle separation by modified surface morphology

Water scarcity is a serious issue faced by communities across the globe, including those in foggy coastal regions, where the air is laden with an alternative source of fresh water. As seen in nature, the Namib desert beetles such as O. unguicularis use their bodies to intercept the inertial fog droplets carried by the wind. We hypothesize that the unique surface features of these beetles' backs are physical adaptations that manipulate flow and hydrodynamic interactions toward enhanced fog collection ability. Through experiments conducted with controlled fog delivery and sensitive measurements of impaction efficiency, complemented by numerical flow simulations, we find mechanisms that are responsible for dramatically increased collection: While flow structure is modulated at the millimetric (morphological) scale to increase droplet slip velocity near target surface, hydrodynamic resistance to contact is decreased by features at the microscopic (roughness) scale.