ESPCI web site
PMMH’s weekly seminar is held every Friday at 11 am (map)
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.
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Recent seminars (8)
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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 - Hughes Chaté (CEA Saclay)
Vendredi 13 décembre de 11h00 à 12h00 - Salle réunion PMMH 1
Modeling suspensions of swarming bacteria with wet Vicsek models
Hugues Chaté SPEC, CEA - Saclay & Beijing CSRC, China After a brief introduction to active matter and some remarks about the development of the field, I will first focus on aligning dry active matter, and in particular on Vicsek-style models, the emblematic models in this class. In a second part, I will show that (...) -
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 - 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 – Scott Waitukaitis (IST Austria)
Vendredi 22 novembre de 11h00 à 12h00 - Salle réunion PMMH 1
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Séminaire PMMH - Hannah Allen (LSCE, CEA Saclay)
Vendredi 15 novembre de 11h00 à 12h00 - Salle réunion PMMH 1
Monitoring atmospheric fossil fuel emissions using radiocarbon and global atmospheric simulations with a transport and inverse modeling system
Independent monitoring and apportioning of CO2 emissions is crucial for the verification of greenhouse gas reductions targeted by international agreements designed for climate change mitigation and adaptation. Radiocarbon (14C), found as a fractional isotope of CO2, can be used as a key tracer for fossil-derived (...)
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)
