HAIRY: Equilibrium, dynamics and flow control of droplets on soft hairy surfaces and channels

Hårete overflater finnes på planteblader, i foringen av blodkapillærer, og i en rekke ingeniørprosesser. Felles for alle disse overflatene er at de ofte interagerer med myke grensesnitt som celler, dråper og bobler. I dette prosjektet vil vi oppdage bevegelsesmønsteret til dråper på hårete overflater og hvordan flytene av disse kan kontrolleres. Prosjektet vil bruke eksperimenter, teori og datasimuleringer for å forstå hvordan dråper interagerer med fibrene på disse overflatene. Prosjektet fokuserer på hvordan egenskapene til fibrene, væskene og overflatene påvirker dråpers oppførsel, både i åpne rom og trange kanaler. Prosjektet vil avdekke dråpebevegelsen og hvordan fibrene reagerer, med mål om å kontrollere hvordan dråpene beveger seg ved å endre overflateegenskapene. Denne forskningen kan føre til nye måter å håndtere dråpeflyt ved å designe hårete overflater.

Surfaces densely covered with soft slender fibers, akin a hairy carpet (shag), that come in contact with a liquid interface are abundant in biological systems and relevant for a wide range of engineering processes. The HAIRY project seeks to unveil the so far unknown flow of droplets as they interact with surfaces covered with soft fibers akin to hairs. The fundamental physics of these flows will be described through experiments, in combination with theory and numerical simulations. More specifically, the project will describe how the properties of the soft material, the liquid and the surface chemistry affects the equilibrium state of droplets and the hairs, both in open systems and as a function of confinement (channels). The droplet flow regimes on these hairy surfaces and channels will be mapped out in experiments and numerical simulations, providing a detailed description of the flow. It is physically rich systems, with dynamics stemming from the close coupling between viscous flow and the elastic surface deformations of the hairs. As the droplet travels across the elastic hairs it will continuously wet and de-wet their tip, leading to contact line detachment from the hairs, which will make the hairs elastically relax in a recoil mechanism giving a memory of the flow. The soft and deformable features of the hairy surface will be utilised to actively alter droplet dynamics by surface modulations by stretching the soft hairy material, as well as exploring how drops traveling along these surfaces may experience lift forces even at very viscous flows allowing for control of droplet paths. The HAIRY project will provide a newfound understanding of the fundamental physics of the interfacial flow dynamics on these soft hairy surfaces, which will provide pathways for engineering hairy surfaces for droplet flow control.