Soft matter comprises micron or sub-micron-sized objects (solid colloidal particles, liquid emulsion drops, air bubbles, polymers...) suspended in a background solvent. In dilute systems, these objects undergo a characteristic erratic motion, due to the collisions with the solvent molecules, as first reported by British botanist Robert Brown for pollen grains. In more concentrated systems, the interactions between the suspended particles lead to slower, more complex dynamics, a crowding effect qualitatively similar to the slowing down of the microscopic dynamics in dense granular systems or molecular amorphous materials, such as glass formers. In this seminar, I'll review the slow dynamics of a variety of soft materials, from model systems for the glass transition (dense suspensions of colloidal hard spheres), to more complex systems such as colloidal gels made of attractive particles or gels made of actin filaments, as found in the cytoskeleton of cells. The emphasis will be on the striking similarities found in the behavior of many systems, in spite of their vastly different structure and composition.

The dynamics of glass-forming liquids is heterogeneous and displays growing spatial correlations upon cooling. Whether such behavior arises from heterogeneities in local structure or more complex forms of amorphous order is a highly debated question. To clarify this issue, we study several model liquids within a coherent simulation framework based on the iso-configurational ensemble. We find that the correlation between the preferred local structure and dynamic heterogeneity is strongly system dependent. The correlation is pronounced in systems that deviate markedly from the mean-field picture of glassy dynamics and weak in models that adhere to it to a good extent. In the model that adheres best to the mean-field paradigm, namely a dense fluid of Gaussian particles, than nature of dynamic heterogeneity differs strikingly from the other liquids: on approaching the mode Coupling critical temperature the fluid develops giant dynamic fluctuations accompanied by nearly Gaussian single-particle dynamics. The observed differences between the models are qualitatively explained in terms of their potential energy landscapes.

Un nanotube de carbone (NT) peut être envisagé comme un enroulement spécifique d’un plan de graphène sur lui-même. La géométrie hélicoïdale ainsi obtenue détermine sa structure moléculaire et par conséquent ses propriétés physiques. En particulier, les NTs sont soit métalliques soit semi-conducteurs selon leur angle d’enroulement et ils présentent des propriétés optiques qui dépendent de leur diamètre. Cependant, ces propriétés ne sont pas modulables.Une méthode élégante pour contrôler et ajuster les propriétés opto-électroniques consiste à élaborer des nano-matériaux hybrides 1D par confinement de molécules dans la cavité des nanotubes. Nous présenterons ici les principaux résultats obtenus après insertion de molécules d’iode [1], d’oligothiophène [2] et de phthalocyanine [3]. Nous montrerons qu’il est possible, essentiellement par spectroscopie Raman, d’étudier les propriétés structurales des molécules encapsulées (organisation supramoléculaire et effets de confinement), la nature des interactions physiques permanentes (dispersive ou avec transfert de charge, entre molécules ou avec les NTs) et de mettre en évidence d’éventuels effets photo-induits.

Sideband holography can be used to get fields images (E0 and E1) of a vibrating object for both the carrier (E0) and the sideband (E1) frequency with respect to vibration. We propose here to record E0 and E1 sequentially, and to image the correlation E1E * 0 . We show that this correlation is insensitive the phase related to the object roughness and directly reflect the phase of the mechanical motion. The signal to noise can be improved by averaging the correlation over neighbor pixel. Experimental validation is made with vibrating cube of wood and with a clarinet reed. At 2 kHz, vibrations of amplitude down to 0.01 nm are detected.

We propose a scheme for a quantum thermal machine made by atoms interacting with a single non equilibrium electromagnetic field. The field is produced by a simple configuration of macroscopic objects held at thermal equilibrium at different temperatures.We show that these machines can deliver all thermodynamic tasks (cooling, heating, and population inversion) by establishing quantum coherence with the body on which they act. Remarkably, this system allows these machines to reach efficiencies at maximum power very close to the Carnot limit, which is much more than in existing models. Our findings offer a paradigm for efficient quantum energy flux management, and can be relevant for both experimental and technological purposes.

Spherical viral shells with icosahedral symmetry are considered as quasicrystalline tilings. Similarly to known Caspar-Klug quasi-equivalence theory, the presented approach also minimizes the number of conformations necessary for the protein molecule bonding with its neighbors in the shell, but is based on different geometrical principles. It is assumed that protein molecule centers are located at vertices of tiles with identical edges, and the number of different tile types is minimal. Idealized coordinates of nonequivalent by symmetry protein positions in six various capsid types are obtained. The approach describes in a uniform way both the structures satisfying the well-known Caspar and Klug geometrical model and the structures contradicting this model.

Les réseaux transitoires auto-assemblés constituent une classe importante de fluides viscoélastiques aux propriétés rhéologiques linéaires particulièrement simples . Après les avoir décrits je tenterai de définir ce qu'est une fracture dans un fluide complexe et j'illustrerai différentes situations de fractures que nous avons explorées en utilisant ses systèmes expérimentaux modèles formulés au laboratoire: fractures induites par cisaillement, fractures en géométrie élongationnelle ( experiences de gouttes pendantes incluant l'étude de la propagation de fractures)), fractures en cellules Hele-Shaw (transition digitation/fracture), fractures dans des nappes liquides de fluides faiblement viso-élastiques . Je montrerai aussi comment nous avons tenté de généraliser la notion de transition fragile/ductile au cas de fluides visco-élastiques.