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Articles
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Séminaire PMMH - M. Mungan (Institute of Biological Physics, University of Cologne)
22 décembre 2023Vendredi 22 décembre 2023 de 11h00 à 12h00 - Salle réunion PMMH 1Memory Formation in Driven Disordered Systems - Dead or Alive
Memory formation and ageing are abundant in many soft matter systems. The disorder underlying these systems gives rise to a rich energy landscape, consisting of a large number of metastable states. These landscapes are accompanied by a plethora of pathways, along which such systems can evolve when exposed to a varying temperature or mechanical load. The resulting dynamics can be rather complex, giving rise to dynamically critical phenomena such as irreversibility and yielding. At the same time, such system exhibit parallels with the adaptive evolution of biological populations in time-varying environments. In this talk I will present a general framework to analyze the dynamics and memory formation of driven disordered systems. I will then show how this framework can be applied to understand both the response of mechanical systems with disorder as well as the antibiotic resistance evolution of a microbial population subject to time-varying drug concentrations.
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Séminaire PMMH - M. Mungan (Institute of Biological Physics, University of Cologne)
19 décembre 2023Vendredi 22 décembre 2023 de 11h00 à 12h00 - Salle réunion PMMH 1Memory Formation in Driven Disordered Systems - Dead or Alive
Memory formation and ageing are abundant in many soft matter systems. The disorder underlying these systems gives rise to a rich energy landscape, consisting of a large number of metastable states. These landscapes are accompanied by a plethora of pathways, along which such systems can evolve when exposed to a varying temperature or mechanical load. The resulting dynamics can be rather complex, giving rise to dynamically critical phenomena such as irreversibility and yielding. At the same time, such system exhibit parallels with the adaptive evolution of biological populations in time-varying environments. In this talk I will present a general framework to analyze the dynamics and memory formation of driven disordered systems. I will then show how this framework can be applied to understand both the response of mechanical systems with disorder as well as the antibiotic resistance evolution of a microbial population subject to time-varying drug concentrations.
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Séminaire PMMH, Joshua Dijksman (UVA)
4 décembre 2023Vendredi 19 janvier de 11h00 à 12h00 - Salle réunion PMMH 1Covalent adaptable polymer networks provide mechanical tunability via molecular and mesoscopic lengthscales
Polymeric materials are ubiquitous in society but also present a large source of waste. There is an ongoing search for polymeric materials that can be better tuned and recycled. One class of polymers that came into the spotlight for this purpose are so-called covalent adaptable polymer networks. Such polymer networks are dynamic due to the reversible nature of some of the bonds. We demonstrate that fine-grained, quantitative control over macroscopic dynamic material properties can be achieved in such materials using the Hammett equation that controls the strength of the dynamic bonds. Moreover, we reveal with Raman spectroscopy that mesoscopic phase separation occurs in these materials. The phase separation can be controlled via concentration and molecular design. The mechanisms of phase separation in dynamic polymer networks are particularly interesting as the reversible nature of the network participates in the structuring of the micro- and macromolecular domains, for which theoretical development is still largely incomplete.
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Séminaire PMMH - Mathilde Reyssat, Gulliver (ESPCI)
4 décembre 2023Vendredi 8 décembre 2023 de 11h00 à 12h00 - Salle réunion PMMH 1Swimming droplets under confinement
Artificial micro-swimmers have recently become a central field of research in soft-matter. A very promising and original type of swimmer developed in our team, consists in pure water droplet swimming in an oil phase containing micelles of surfactant. The droplet's activity comes from the formation of swollen micelles at its interface which induces Marangoni stresses and then motion of the droplets.
We investigate experimentally the behavior of such self-propelled water-in-oil droplets, confined in capillaries of different square and circular cross-sections. Stretched circular capillaries have been used to explore even stronger confinement. Within the most constricted regions, droplets elongate very strongly. These extremely long droplets reveal unexpected behaviors during their motion, in particular regarding their stability.
We build up on the Bretherthon formalism to rationalize this new kind of self-motion of confined droplets in a tube, not anymore driven by pressure or flow rate but rather by locally-induced interfacial stresses.
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Séminaire PMMH - Arthur Alexandre (EPFL)
4 décembre 2023Vendredi 15 décembre 2023 de 11h00 à 12h00 - Salle réunion PMMH 1Dispersion in heterogeneous media : how boundaries shape transport properties
Identifying transport properties of tracer particles in heterogeneous media at large time and length scales has applications in wide range of physical systems including microfluidics, hydrology, chemical engineering or soft matter. The effective diffusivity is a crucial input for problems of mixing, sorting, chemical delivery, as well as chemical reactions. Spatial variations of diffusion and advection can lead to drastic changes in the effective diffusion constant with respect to homogenous systems. Classic examples include Taylor dispersion in hydrodynamics, and the decrease of diffusivity due to the crowding effect produced by spatially-varying boundaries or the presence of an external periodic potential.
In particular, the effect of the confining geometry on the effective diffusivity has been widely studied, but the vast majority of existing theories focuses on perfectly reflecting boundaries. Using a general framework that incorporates surface-mediated diffusion, we show analytically that making surfaces or obstacles attractive can accelerate dispersion [1]. We notably show that this enhancement of diffusion can exist even when the surface diffusion constant is smaller than that in the bulk.
Our formalism can be generalized to encompass drifts or spatially-dependent diffusion tensor [2, 3]. Indeed, his spatial dependency results from hydrodynamic interactions between the tracer and the wall and are not negligible in the situation of strong confinement. In particular, we examine how the latter mechanism modifies the tracer displacement distribution by computing cumulants beyond the mean-squared displacement. Our results were confirmed by numerical simulations and experimental data.
References
[1] Alexandre, A., Mangeat, M., Guérin, T. & Dean, D. S. How stickiness can speed up diffusion in confined systems. Physical Review Letters 128, 210601 (2022).
[2] Alexandre, A., Gu´erin, T. & Dean, D. S. Generalized taylor dispersion for translationally invariant microfluidic systems. Physics of Fluids 33 (2021).
[3] Alexandre, A. et al. Non-gaussian diffusion near surfaces. Physical Review Letters 130, 077101 (2023).