The constituents of jammed and glassy soft materials are so densely packed and/or so tightly bound that their microscopic dynamics are orders of magnitude slower than in dilute systems. Examples of such materials include, among others, concentrated colloidal suspensions or emulsions, polymer or particle gels, surfactant phases, foams. Our research focuses on the spontaneous (e.g. due to thermal energy) dynamics of these materials, as well as on their behavior in response to an external drive, e.g. a mechanical or thermal forcing. We leverage on our expertise in the formulation of well-defined supramolecular systems with original properties, combined with home-designed devices allowing a thorough characterization of the structure and dynamics of the system and a fine control of the imposed drive.
Fractures propagating in a dense corn starch suspension. The suspension is confined between two parallel plates separated by a thin gap. The fracture is caused by the fast injection of solvent, at a point about 3 cm from the field of view. The field of view is about 1 cm2. The sample is illuminated using laser light : the temporal fluctuations of the resulting speckle patter carry information on the microscopic dynamics and the velocity field (see Photon Correlation Imaging in Glassy and Jammed Soft Matter). By Frederic Lechenault, Serge Mora and Luca Cipelletti.
Glassy and jammed soft matter People involved : L. Cipelletti, A. Philippe, V. Roger Most soft materials that exhibit a predominantly solid-like mechanical behavior also exhibit complex slow dynamics at a microscopic level. These dynamics are actively investigated because some of these systems may be regarded as model systems to tackle long-standing problems in condensed matter (e.g. colloidal hard spheres, HS, for the glass transition), and because slow dynamics play an important role in (...)
Material failure in soft matter (i) Morphology and propagation of a crack in a transient network. People involved : G. Foyart, L. Cipelletti, C. Ligoure, S. Mora, L. Ramos A self-assembled transient network is a complex fluid consisting of reversibly cross-linked polymers in solution. Using high speed videomicroscopy, we have tracked the fracture propagation during pendant drop experiments of a model transient network made from oil in water microemulsion droplets reversibly linked (...)
Morphogenesis and elastic instability of surfaces and interfaces (i) Elastic surfaces instability : Biot instability revisited People involved : M. Abkarian, S. Mora. Collaboration : Y. Pomeau (University of Arizona, Tucson) Many years ago M. A. Biot predicted that, when compressed by a finite amount, a piece of elastic rubber-like material becomes unstable for a small undulation of its surface. We have shown that this instability can be observed under homogeneous compressions : cusps (...)