BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Memento EPFL// BEGIN:VEVENT SUMMARY:The dynamics of confined droplets DTSTART:20170425T141500 DTEND:20170425T151500 DTSTAMP:20260924T071711Z UID:217a6a1e6e5693e68e1a6a465c3f5d5952e3e8e762d78e5d2e1eef0b CATEGORIES:Conferences - Seminars DESCRIPTION:Etienne Reyssat and Ludovic Keiser Laboratoire de Physique et Mécanique des Milieux Hétérogènes (PMMH\, ESPCI) Paris\nThe dynamics o f confined droplets has been extensively studied during the last decades\, in the footsteps of the development of digital microfluidics. In the fiel d of oil recovery\, numerous phenomena lead to the emulsification of petro leum while transported across a reservoir\, e.g. viscous fingering or snap -off. The understanding of the peculiar dynamics of confined droplets and emulsions is thus of crucial importance.\nIn a first part\, we will discus s the shapes and velocities of completely wetting droplets of oil sliding under gravity between closely spaced parallel walls (Hele-Shaw cell). Visc ous dissipation opposing the motion takes place both in the bulk of the li quid and in the vicinity of contact lines. In this model geometry\, bulk a nd line effects may be measured independently. We investigate contact line dissipation by studying the motion of droplets on pre-wetted surfaces\, a way to regularize the contact line singularity in a controlled way.\n\nIn a second part\, we focus on the dynamics of non-wetting droplets of oil c onfined in a vertical Hele-Shaw cell filled with a much less viscous sur factant solution. The oil droplets are denser than the aqueous solution an d move at constant speed driven by gravity. The surfactant solution comple tely wets the walls\, and a thin lubrication film separates the oil drople ts from the walls. For a cell with smooth walls\, two main dynamical regim es are characterized as the gap between the walls is varied. Viscous dissi pation is found to dominate either in the droplet or in the lubrication fi lm. A sharp transition between both regimes is observed and successfully c aptured by asymptotic models. For a cell with rough walls\, that transitio n is found to be dramatically altered. We show that droplets are generally much slower in a rough Hele-Shaw cell\, in comparison with a similar smoo th cell. Building up on the seminal work of Seiwert et al. (JFM\, 2011) on film deposition by dip coating on a rough surface\, we shed light on non- trivial friction processes resulting from the interplay of viscous dissipa tion at the front of the droplet\, in the lubrication film and in the bulk of the droplet.\n\nThe dynamics of confined droplets has been extensively studied during the last decades\, in the footsteps of the development of digital microfluidics. In the field of oil recovery\, numerous phenomena l ead to the emulsification of petroleum while transported across a reservoi r\, e.g. viscous fingering or snap-off. The understanding of the peculiar dynamics of confined droplets and emulsions is thus of crucial importance. \n\nIn a first part\, we will discuss the shapes and velocities of complet ely wetting droplets of oil sliding under gravity between closely spaced p arallel walls (Hele-Shaw cell). Viscous dissipation opposing the motion ta kes place both in the bulk of the liquid and in the vicinity of contact li nes. In this model geometry\, bulk and line effects may be measured indepe ndently. We investigate contact line dissipation by studying the motion of droplets on pre-wetted surfaces\, a way to regularize the contact line si ngularity in a controlled way.\n\nIn a second part\, we focus on the dynam ics of non-wetting droplets of oil confined in a vertical Hele-Shaw cell filled with a much less viscous surfactant solution. The oil droplets are denser than the aqueous solution and move at constant speed driven by gra vity. The surfactant solution completely wets the walls\, and a thin lubri cation film separates the oil droplets from the walls. For a cell with smo oth walls\, two main dynamical regimes are characterized as the gap betwee n the walls is varied. Viscous dissipation is found to dominate either in the droplet or in the lubrication film. A sharp transition between both re gimes is observed and successfully captured by asymptotic models. For a ce ll with rough walls\, that transition is found to be dramatically altered. We show that droplets are generally much slower in a rough Hele-Shaw cell \, in comparison with a similar smooth cell. Building up on the seminal wo rk of Seiwert et al. (JFM\, 2011) on film deposition by dip coating on a r ough surface\, we shed light on non-trivial friction processes resulting f rom the interplay of viscous dissipation at the front of the droplet\, in the lubrication film and in the bulk of the droplet.\n  LOCATION:ME B10 https://plan.epfl.ch/theme/generalite_thm_plan_public?dim_ floor=1&lang=fr&dim_lang=fr&baselayer_ref=grp_backgrounds&tree_groups=cent res_nevralgiques%2Cacces%2Cmobilite_reduite%2Censeignement%2Ccommerc STATUS:CONFIRMED END:VEVENT END:VCALENDAR