Modeling of self-driven directional movement of underwater oil droplets on bio-inspired nano-coated 3D-printed conical models

Abstract

The contamination of water with oil from industrial processes has become a worldwide problem that requires the development of efficient, reliable and economical separation methods. Inspired by droplet movements on spider silk, we present in this contribution a model of the separation of oil and water that is based on the effect that liquid droplets move on cone-shaped structures, driven by capillary forces. We extend existing models to barrel-shaped oil droplets that move, completely surrounded by water, along suitably shaped filaments and derive the forces acting on the droplets from first principles of physics. By bringing together the results of the theoretical model and the corresponding experiments, the underlying mechanism of the directional movement of droplets in another liquid medium is thoroughly investigated and modeled. The resulting model predicts the dependence of the droplet motion on time and on “system defining” parameters, such as droplet size, viscosity, and dynamic contact angles formed between droplet and filament surface. We expect this work to pave the road for the design and preparation of bionic structures in the field of droplet transport phenomena, which is of great interest in various applications.