2019 EPFL doctorate Award - Finalist – Gioele Balestra
Special distinction from the selection committee to Gioele Balestra for his thesis “Pattern formation in thin liquid films: from coating-flow instabilities to microfluidic droplets”
EPFL thesis n°8828 (2018)
Thesis director: Prof. F. Gallaire
Nature and technical applications abound with thin viscous flows, ranging from the lava flow on volcanoes to the lubricating layer around confined droplets in microchannels. We all have already observed that thin-film flows often form well-defined patterns, as the tears in a glass of wine, or the crystalline-like pattern of pendent droplets under the kitchen lid.
The aim of this thesis is to investigate the mechanisms underpinning the pattern formation in thin-film flows for different configurations. A theoretical model is developed and complemented with advanced stability analyses, numerical simulations and experiments.
We show that the gravity-driven instability of a liquid film under curved or inclined substrates is at the origin of the fascinating karst formations encountered in limestone caves. Furthermore, we find and rationalize a stable regime of these film flows that can be harnessed to produce hemispherical elastic shells in a very robust and versatile manner.
We also provide a detailed characterization of the thin-film profiles around confined droplets, key for a better prediction of their dynamics in microfluidic devices.
In spite of the broad range of scales considered, we show that all the treated problems and the pattern selections can be described by similar lubrication equations.