ESPCI web site
Le séminaire hebdomadaire du laboratoire PMMH a lieu tous les vendredis à 11h, au premier étage Barre Cassan, campus Jussieu (plan).
Sylvain Patinet
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.
Séminaires (10)
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Séminaire PMMH – Scott Waitukaitis (IST Austria)
Vendredi 22 novembre de 11h00 à 12h00 - Salle réunion PMMH 1
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Séminaire PMMH - Denis Dumont (IUSTI Marseille)
Vendredi 29 novembre de 11h00 à 12h00 - Salle réunion PMMH 1
Rheology of sticky grains
In many powder technology processes, coating is applied to fine particles to control their properties or functionalize them. We investigated the role of a polymer coating made of PBS on silica beads. This material has been originally designed as a model cohesive granular material, whose cohesion can be finely (...) -
Séminaire PMMH - Xanthippi Markenscoff (University of California San Diego)
Vendredi 6 décembre de 11h00 à 12h00 - Salle réunion PMMH 1
Instabilities of nucleation and growth of a phase change defect
Department of Mechanical and Aerospace Engineering University of California San Diego La Jolla, CA 92093-0411 Abstract A defect of phase change in density and moduli modeled as a self-similarly expanding Eshelby ellipsoidal inclusion can nucleate and grow under a critical loading. The ellipsoid possesses the (...) -
Séminaire PMMH - Xanthippi Markenscoff (University of California San Diego)
Vendredi 6 décembre de 11h00 à 12h00 - Salle réunion PMMH 1
Instabilities of nucleation and growth of a phase change defect
Department of Mechanical and Aerospace Engineering University of California San Diego La Jolla, CA 92093-0411 Abstract A defect of phase change in density and moduli modeled as a self-similarly expanding Eshelby ellipsoidal inclusion can nucleate and grow under a critical loading. The ellipsoid possesses the (...) -
Séminaire PMMH - Hughes Chaté (CEA Saclay)
Vendredi 13 décembre de 11h00 à 12h00 - Salle réunion PMMH 1
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Séminaire PMMH – Joseph Ackerman (Lab. Jean Perrin, Sorbonne Université)
Vendredi 20 décembre de 11h00 à 12h00 - Salle réunion PMMH 1
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Séminaire PMMH – Joseph Ackerman (Lab. Jean Perrin, Sorbonne Université)
Vendredi 20 décembre de 11h00 à 12h00 - Salle réunion PMMH 1
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Séminaire PMMH - Ludovic Berthier, Gulliver
Vendredi 24 janvier 2025 de 11h00 à 12h00 - Salle réunion PMMH 1
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Séminaire PMMH - Christophe Denoual, CEA
Vendredi 14 février 2025 de 11h00 à 12h00 - Salle réunion PMMH 1
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Séminaire PMMH - Christophe Denoual, CEA
Vendredi 14 février 2025 de 11h00 à 12h00 - Salle réunion PMMH 1
Instructions générales pour les conférenciers
Le public du séminaire est très hétérogène (rien qu’au PMMH nous travaillons sur des thématiques très diverses, mécanique des fluides, des milieux granulaires, des solides, physique statistique, physique du mouillage, micro-fluidique, biophysique,...) l’objectif est donc de ne pas faire un séminaire trop spécialiste : au moins la première moitié du séminaire à un niveau accessible pour celui qui ne connaît rien sur le sujet.
Le séminaire a lieu à 11h. rendez-vous 15 minutes avant pour installer et tester la projection.
Le séminaire dure environ 45 minutes pour laisser un peu de temps pour discuter à la fin.
- 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
Lien vers séminaires café (internes, tous les jeudis)
