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SUMMARY:The latest from LFMI: some stories of Fluid Mechanics and Instabil
 ities
DTSTART:20180419T161500
DTEND:20180419T171500
DTSTAMP:20260916T191106Z
UID:5197dfb73bc108cc4bacb9d1b92bb4cc68756fda8e4f8527c7f0f6d3
CATEGORIES:Conferences - Seminars
DESCRIPTION:Giacomo Gallino\, Gioele Balestra\, and Ludovic Keiser - EP
 FL STI IGM Laboratory of Fluid Mechanics and Instabilities (LFMI) \nAbs
 tract\nPhysics of bubble-propelled microrockets by Giacomo Gallino\nSelf-p
 ropelled artificial micro-motors have attracted much attention both as fun
 damental examples of active matter and for their potential biomedical appl
 ications (e.g. drug delivery\, cell sorting). A popular design exploits th
 e 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 n
 umerical simulations of the chemical problem and viscous hydrodynamics\, w
 e analyse the formation\, growth and motion of the bubbles inside the micr
 o-motor and the resulting swimming motion. Our results shed light on the f
 undamental hydrodynamics of the propulsion of conical swimmers and may hel
 p to improve the efficiency of these machines.\n\nRayleight-Taylor instabi
 lity under curved subtrates by Gioele Balestra\nA liquid film coated on th
 e underside of a planar substrate is subject to the Rayleigh-Taylor instab
 ility 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 a
 symptotically stable to infinitesimal perturbations. Nevertheless\, we hav
 e found that the system acts as a transient amplifier and may from drippin
 g droplets. Here\, we consider coatings inside cylindrical and spherical 
 substrates and demonstrate that additional instability patterns arise. A l
 inear stability analysis based on lubrication equations is performed and t
 he results are found to be in good agreement with experiments and numerica
 l simulations.\n\nMarangoni bursting by Ludovic Keiser\nAt the surface of 
 a sunflower oil bath\, a drop of water adopts a lenticular shape. Converse
 ly\, alcohol totally wets the oil and spreads. Depositing a mixture of wat
 er and alcohol reveals a spectacular fragmentation phenomenon. If it conta
 ins enough alcohol\, the drop spontaneously spreads and fragments into a m
 yriad of minute droplets whose size strongly depends on the initial mixtur
 e 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 radiu
 s and timescale of spreading. Other combinations of liquids also lead to t
 his fascinating phenomenon and further confirm our scenario.​\n\nBio\nAl
 l speakers are active members of the LFMI group.\nGiacomo Gallino is a las
 t year PhD student\, focusing on numerical studies of two phase systems.\n
 Gioele Balestra is a last year PhD student\, with interest in hydrodynamic
  instabilities of thin flows.\nLudovic Keiser is a fresh post-doctoral res
 earcher. He studies experimentally a variety of capillary phenomena.\n 
LOCATION:MED 0 1418 https://plan.epfl.ch/?room==MED%200%201418
STATUS:CONFIRMED
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