The latest from LFMI: some stories of Fluid Mechanics and Instabilities
Event details
| Date | 19.04.2018 |
| Hour | 16:15 › 17:15 |
| Speaker | Giacomo Gallino, Gioele Balestra, and Ludovic Keiser - EPFL STI IGM Laboratory of Fluid Mechanics and Instabilities (LFMI) |
| Location | |
| Category | Conferences - Seminars |
Abstract
Physics of bubble-propelled microrockets by Giacomo Gallino
Self-propelled artificial micro-motors have attracted much attention both as fundamental examples of active matter and for their potential biomedical applications (e.g. drug delivery, cell sorting). A popular design exploits the catalytic decomposition of a fuel (e.g. hydrogen peroxide) on the active surface of the motor to produce oxygen bubbles that propel the swimmer, effectively converting chemical energy into swimming motion. We focus here on a conical shape swimmer with chemically-active inner surfaces. Using numerical simulations of the chemical problem and viscous hydrodynamics, we analyse the formation, growth and motion of the bubbles inside the micro-motor and the resulting swimming motion. Our results shed light on the fundamental hydrodynamics of the propulsion of conical swimmers and may help to improve the efficiency of these machines.
Rayleight-Taylor instability under curved subtrates by Gioele Balestra
A liquid film coated on the underside of a planar substrate is subject to the Rayleigh-Taylor instability so that its interface deforms into waves that lead to the formation of dripping droplets. When the substrate is curved, gravity not only acts as the destabilizing force at the origin of the instability, but also as a stabilizing force originating in the progressive drainage of the film. As a consequence, a two-dimensional thin-film in a circular geometry is asymptotically stable to infinitesimal perturbations. Nevertheless, we have found that the system acts as a transient amplifier and may from dripping droplets. Here, we consider coatings inside cylindrical and spherical substrates and demonstrate that additional instability patterns arise. A linear stability analysis based on lubrication equations is performed and the results are found to be in good agreement with experiments and numerical simulations.
Marangoni bursting by Ludovic Keiser
At the surface of a sunflower oil bath, a drop of water adopts a lenticular shape. Conversely, alcohol totally wets the oil and spreads. Depositing a mixture of water and alcohol reveals a spectacular fragmentation phenomenon. If it contains enough alcohol, the drop spontaneously spreads and fragments into a myriad of minute droplets whose size strongly depends on the initial mixture composition. Marangoni flows resulting from the differential evaporation of alcohol and water play a key role in this self-emulsification process. The intricate coupling of hydrodynamics, wetting and evaporation is well captured by analytical scaling laws that predict the characteristic radius and timescale of spreading. Other combinations of liquids also lead to this fascinating phenomenon and further confirm our scenario.
Bio
All speakers are active members of the LFMI group.
Giacomo Gallino is a last year PhD student, focusing on numerical studies of two phase systems.
Gioele Balestra is a last year PhD student, with interest in hydrodynamic instabilities of thin flows.
Ludovic Keiser is a fresh post-doctoral researcher. He studies experimentally a variety of capillary phenomena.
Physics of bubble-propelled microrockets by Giacomo Gallino
Self-propelled artificial micro-motors have attracted much attention both as fundamental examples of active matter and for their potential biomedical applications (e.g. drug delivery, cell sorting). A popular design exploits the catalytic decomposition of a fuel (e.g. hydrogen peroxide) on the active surface of the motor to produce oxygen bubbles that propel the swimmer, effectively converting chemical energy into swimming motion. We focus here on a conical shape swimmer with chemically-active inner surfaces. Using numerical simulations of the chemical problem and viscous hydrodynamics, we analyse the formation, growth and motion of the bubbles inside the micro-motor and the resulting swimming motion. Our results shed light on the fundamental hydrodynamics of the propulsion of conical swimmers and may help to improve the efficiency of these machines.
Rayleight-Taylor instability under curved subtrates by Gioele Balestra
A liquid film coated on the underside of a planar substrate is subject to the Rayleigh-Taylor instability so that its interface deforms into waves that lead to the formation of dripping droplets. When the substrate is curved, gravity not only acts as the destabilizing force at the origin of the instability, but also as a stabilizing force originating in the progressive drainage of the film. As a consequence, a two-dimensional thin-film in a circular geometry is asymptotically stable to infinitesimal perturbations. Nevertheless, we have found that the system acts as a transient amplifier and may from dripping droplets. Here, we consider coatings inside cylindrical and spherical substrates and demonstrate that additional instability patterns arise. A linear stability analysis based on lubrication equations is performed and the results are found to be in good agreement with experiments and numerical simulations.
Marangoni bursting by Ludovic Keiser
At the surface of a sunflower oil bath, a drop of water adopts a lenticular shape. Conversely, alcohol totally wets the oil and spreads. Depositing a mixture of water and alcohol reveals a spectacular fragmentation phenomenon. If it contains enough alcohol, the drop spontaneously spreads and fragments into a myriad of minute droplets whose size strongly depends on the initial mixture composition. Marangoni flows resulting from the differential evaporation of alcohol and water play a key role in this self-emulsification process. The intricate coupling of hydrodynamics, wetting and evaporation is well captured by analytical scaling laws that predict the characteristic radius and timescale of spreading. Other combinations of liquids also lead to this fascinating phenomenon and further confirm our scenario.
Bio
All speakers are active members of the LFMI group.
Giacomo Gallino is a last year PhD student, focusing on numerical studies of two phase systems.
Gioele Balestra is a last year PhD student, with interest in hydrodynamic instabilities of thin flows.
Ludovic Keiser is a fresh post-doctoral researcher. He studies experimentally a variety of capillary phenomena.
Practical information
- General public
- Free
Organizer
- MEGA.Seminar Organizing Committee (Anna Lee, Lorenzo Benedetti, Hervé Elettro, Till Junge, Francesco Maresca, Roozbeh Rezakhani, Dong Yan, Noelia Simone)