Programme > Invited presentations

Axelle Amont (Institut de Physique, CNRS/Université de Rennes) - Creep response of granular materials

Stéphanie Deboeuf (Institut d'Alembert, CNRS,/Sorbonne Université) - Compaction de plaques minces confinées: de l’Elastica d’Euler à des configurations désordonnées

Paolo Edera (C3M, CNRS/ESPCI Paris) - Mechanical Tuning of Residual Stress, Memory, and Aging in Soft Glassy Materials

Yann-Edwin Keta (PMMH, CNRS/ESPCI Paris/Sorbonne Université/Université Paris Cité) - Correlated cell movements drive epithelial finger formation

Gabriel Le Marié (Centre for Quantum Technologies CQT-NUS, Singapore) - TBA

Ananyo Maitra (Laboratoire de Physique Theorique et Modelisation LPTM, Université Cergy-Pontoise) - Active ordering in disordered environments

Laurence Ramos (Laboratoire Charles Coulomb L2C, CNRS/ Université Montpellier) - Colloidal rheology in a drop

------------------------------

Axelle Amont (Institut de Physique, CNRS/Université de Rennes) - Creep response of granular materials

Abstract TBA.

Stéphanie Deboeuf (Institut d'Alembert, CNRS,/Sorbonne Université) - Compaction de plaques minces confinées: de l’Elastica d’Euler à des configurations désordonnées

Abstract TBA.

Paolo Edera (C3M, CNRS/ESPCI Paris) - Mechanical Tuning of Residual Stress, Memory, and Aging in Soft Glassy Materials

Glassy materials rapidly quenched from a liquid to a solid state upon flow cessation or cooling solidify in an out-of-equilibrium configuration, trapping residual stresses and retaining the memory of the processing conditions for very long times, which compromises their physical characterization and can adversely affect processing operations. Erasing the mechanical history encoded in disordered materials constitutes a great challenge. Here, we address this problem using experiments and particle dynamic simulations for the case of colloidal glasses made of soft particles densely packed at high volume fractions. We propose a conceptual framework that connects residual stresses, directional memory, and aging of colloidal glasses to the distribution of local shear stresses in the shearing plane. The mean value of the distribution corresponds to the macroscopic stress, the skewness carries information about directional memory, and the standard deviation is related to mechanical aging. Periodically training soft particle glasses near the yield point with a sequence of stress-controlled oscillations provides a fine-tuning of the particle stress distribution. Asymmetric shear stress distributions resulting from previous flow are transformed into symmetric distributions, thereby successfully erasing residual stresses and directional memory. The same methodology is successfully applied to colloidal and polymer gels with thixotropic properties, suggesting that it is general and may be extended to other classes of disordered materials.

Yann-Edwin Keta (PMMH, CNRS/ESPCI Paris/Sorbonne Université/Université Paris Cité) - Correlated cell movements drive epithelial finger formation

Sheets of epithelial cells form protective barriers in multicellular organisms. When damaged, finger-like protrusions form at the advancing edge, closing the damaged area. Due to the resemblance to fluid spreading, existing models typically invoke instability mechanisms to explain the onset of fingers. Combining in vitro experiments on freely expanding MDCK cell monolayers with simulations of the self-propelled Voronoi model and an active viscoelastic theory, we show that instead fingers form spontaneously due to emergent, correlated cell motion within the cell layer and simply represent long-lived active fluctuations of the boundary. Simulations and theory both quantitatively match spatiotemporally correlated cell motion measured in the interior of the monolayer. To capture finger formation, we model the actomyosin cable at the advancing edge as a contractile semi-flexible polymer driven by correlated active noise representing the interior. The model not only exhibits spontaneous finger formation but also quantitatively predicts tangent-tangent and roughness correlation functions of the edge in space and time, as well as fluctuation spectra. Our results, therefore, indicate that correlated cell movements lead to robust finger formation, without the need for any feedback mechanism, suggesting that leader cells, cell-cell signalling, and division modulate an intrinsic process instead of causing it.

Gabriel Le Marié (Centre for Quantum Technologies CQT-NUS, Singapore) - TBA

Abstract TBA.

Ananyo Maitra (Laboratoire de Physique Theorique et Modelisation LPTM, Université Cergy-Pontoise) - Active ordering in disordered environments

It is by now well known that motility allows active polar fluids to remain ordered in lower dimensions than their passive counterparts. It is less known that the stabilising effect of motility is even more pronounced in disordered environments. Indeed, I will show that a particular kind of active polar fluids can retain orientational order in two dimensions even in the presence of random-field disorder. This is because motility has an "annealising" effect on time-independent disorder. In the second part of the talk, I will shift my attention to active phases that break translational symmetry––specifically, polar smectics and solids––and demonstrate that, even here, motility anomalously stabilises order. Indeed, the equal-time statistics of displacement fluctuations of motile smectics in d dimensions with quenched disorder are equivalent to time-displaced correlations of the height field in the d-1-dimensional KPZ equation. For one class of motile solids, I will show that the equal-time displacement correlations in the presence of quenched disorder are only as large as the equal-time displacement correlations of passive solids in the absence of quenched disorder, again attesting to the annealising effect of motion.

Laurence Ramos (Laboratoire Charles Coulomb L2C, CNRS/ Université Montpellier) - Colloidal rheology in a drop

The realm of solid-like colloid-based materials is vast, with a wide variety of structures. Rationalizing the link between the structures and the mechanical properties of this class of materials is a formidable task. However, measuring the rheological features of solid-like colloid-based materials is not easy, especially because of the interaction of the colloidal material with solid surfaces that may impact the sample rheological response submitted to a shear deformation. In order to suppress possible artefacts due to interactions with surfaces, we have developed a strategy based on the use of millimetric drops. We use a multiscale approach combining macroscopic mechanical measurements and imaging with microscopic dynamical and structural measurements to probe colloidals gel confined in a drop. In this framework, I will present several experimental results from the decoupling between structure and elasticity in colloidal gels under isotropic compression o the brittle-to-ductile transition of beads of colloidal gels.