How grooves control droplet growth, transport and release

Water management on surfaces underpins applications ranging from atmospheric water harvesting to heat exchange and surface cleaning. Many existing strategies rely on chemical coatings or micro-texturing, which can be fragile, costly, or difficult to scale. This thesis explores an alternative approach based on simple geometric features, focusing on whether grooves alone can collect, guide, and release small volumes of water on vertical substrates.

We investigate four representative systems that span different flow configurations and degrees of confinement. On fibers and fiber bundles, we show that grooves naturally appearing between strands reorganize droplet dynamics by modifying the film left behind the droplet, reducing dissipation and increasing sliding speed. Under condensation on a vertical plate, we demonstrate that groove spacing selects the drainage pathway: large spacings favor gravitational shedding, while small ones confine droplets to the plateaus and redirect transport into the grooves. At the lower edge of such plates, groove geometry determines the disposition and frequency of droplet dripping. Finally, in a minimal configuration consisting of two parallel grooves, we show that geometry alone can stabilize a thin water film over more than one hundred capillary lengths. At groove termini, the film breaks and releases a droplet through a cyclic sequence of events.

Across these systems, a common principle emerges: groove acts as a minimal feature that structures the flow. Grooves define where liquid accumulates, how it moves, and when it detaches, enabling robust control without coatings or complex fabrication. These findings suggest that simple geometric design can serve as the foundation for scalable, passive, and durable water-handling surfaces, and they outline the key operations needed for a future geometry-driven millifluidic platform.