Film coating by directional droplet spreading on fibers

Plants and insects use slender conical structures to transport collect small droplets, which are propelled along the due capillary action. These droplets can deposit a fluid film during their motion, but despite its importance many biological systems industrial applications properties of deposited unknown. We characterise deposition by developing an asymptotic analysis together with experimental measurements numerical simulations based on lubrication equation. show that thickness depends significantly both fiber radius droplet size, highlighting coating is affected finite size effects relevant fibres any geometry. demonstrate changing while mean Capillary number fixed, change order magnitude or more. self-propelled have significant potential create passively coated structures.