ESPCI web site
PMMH’s weekly seminar is held every Friday at 11 am (map)
Alice Pelosse
Stéphane Perrard
Etienne Reyssat
Virgile Thiévenaz
PMMH
BARRE CASSAN
BAT A 1ER ETAGE CASE 18
7 QUAI SAINT BERNARD
75005 PARIS
France
Tel : (33) 1 40 79 45 22
Séminaire PMMH – Scott Waitukaitis (IST Austria)
Le Lapin Électrostatique : Static Electricity is an Unpredictable Little Bunny
"Static electricity" defies our best attempts to make sense of it. More scientifically referred to as contact electrification (CE), the effect seems straightforward—touch two neutral materials together, separate them, and they will have exchanged some electrical charge. Simple as this sounds, the effect is plagued by unpredictability, and we don't even know what is transferred (e.g., ions vs. electrons), let alone why. In my group, we focus on CE between "identical" materials, which, though counterintuitive, has long been known to occur. I will discuss two sets of experiments on this same-material CE, which are helping us tame the unpredictability and get closer to the mechanism. In the first, we use acoustic levitation to study the charging of an SiO2 sphere as it bounces on an SiO2 plate. We test a leading hypothesis for same-material CE, i.e., that it is due to local variability in surface properties, and show that this is not the case. Going further, we reveal that there is a critical dependence on sample history, especially RH exposure, temperature, and surface treatment, which points to a key role played by surface adsorbates. In the second experiment, we study the charge exchange between soft polymers—identically prepared samples of PDMS. Measuring the charge exchange for all pair combinations of an ensemble, we find they begin charging randomly, but over time evolve into a triboelectric series—i.e., a transitive ordering based on the polarity of the charge acquired. We find that this is caused by the act of contact itself ; samples that have experienced more contacts in their history charge negatively to ones that have experienced less. Based on this observation, we develop a model that explains why our materials evolve into a series, and going further leverage it to control the charging behavior. Ultimately, we discover that this memory effect is due to nanoscale changes in surface morphology, pointing to a mechanism intimately coupled with tribology and contact mechanics.
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Seminars (5)
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Séminaire PMMH – Philippe Beltrame (U. Avignon)
Vendredi 27 mars de 11h00 à 12h00 - Salle réunion PMMH 1
Ratchet Effect for Selective Transport of Microparticles in Fluid Suspension
The ratchet effect enables directed transport of particles in noisy systems, even in the absence of a net force (zero bias). When exploited in periodic structures, this phenomenon paves the way for innovative applications in selective microparticle sorting. This seminar will present a theoretical analysis of (…) -
Séminaire PMMH – Jonas Miguet (MSC, Univ. Paris Cité)
Vendredi 3 avril de 11h00 à 12h00 - Salle réunion PMMH 1
Antibubbles : optical interferometry, gas transfers and acoustic signature
An antibubble is a spherical thin film of gas, that encapsulates a droplet, within a liquid medium. The typical size of an antibubble is one centimeter while the thickness of the gas film is of micrometric order. Because of the higher hydrostatic pressure at the bottom, the gas film undergoes a (…) -
Séminaire PMMH – Gautier Verhille (IRPHÉ)
Vendredi 10 avril de 11h00 à 12h00 - Salle réunion PMMH 1
Formation and fragmentation of fiber aggregate in turbulent flows
Fiber aggregates are commonly encountered in environmental and industrial flows (paper industry, fiber recycling, etc.). However, the physical mechanisms leading to their formation are still misunderstood. Hence, there is still no clear answer to simple questions such as : how long will it take for an aggregate to (…) -
Séminaire PMMH – Nicolas Roméo (James Franck Institute, Chicago)
Vendredi 17 avril de 11h00 à 12h00 - Salle réunion PMMH 1
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Séminaire PMMH – Pas de séminaire
Vendredi 24 avril de 11h00 à 12h00 - Salle réunion PMMH 1
The audience is composed of people with rather heterogeneous backgrounds including specialists in solids, fluids, granular flows, statistical physics... so the idea is to keep your talk understandable by people not necessarily working in your field... The seminar time slot runs from 11am to noon so the best is to make the talk last around 45 minutes to leave some time for discussion.
- Séminaires ESPCI-ENS de biophysique
- Séminaires du Département de Physique de l’ENS
- Séminaires du Laboratoire d’Hydrodynamique de l’X
- Séminaire de Mécanique d’Orsay (page web FAST)
- Séminaire de Mécanique d’Orsay (page web LIMSI)
- Séminaire de Mécanique des Fluides de l’Institut Jean le Rond d’Alembert
- Séminaires du laboratoire MSC, Paris VII
- Séminaires Gulliver
Link to cofee seminar (internal, every Thursday)
