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Séminaires à venir
Applying Soft Materials to Real World Problems.
Larry Hough Complex Assemblies of Soft Matter Laboratory (COMPASS), CNRS, University of Pennsylvania, Rhodia
Mardi 7 septembre - 14h30 - bibliothèque escalier H
The Complex Assemblies of Soft Matter Lab (COMPASS UMI 3254) is a unique collaboration between the CNRS, Rhodia and the University of Pennsylvania. The COMPASS lab is a team of scientists with differentiating capabilities in the creation, manipulation and understanding of soft materials. The team is dedicated to finding sustainable innovative solutions to real world problems. The three main themes of the lab are water scarcity, energy storage and transfer, and sustainable formulations. In this talk, an overview of the activities will be presented. 1) Water Scarcity : The goal of this project is to increase the amount water available to roots of crops and reduce overall water consumption. Studies will be presented on flow in fragile porous media, clogging mechanisms and root growth in the presence of drainage and evaporation. 2) Energy Transfer and Storage : Studies will be presented on new formulations based on organic components that are good candidates for the replacement of Indium Tin Oxide. In addition, studies will be presented on catalytic inks for the reduction of platinum in fuel cell devices. 3) Sustainable Formulations : Studies will be presented based on a unique novel system, temperature sensitive microgels. These microgels are used to understand jamming and melting behavior in real time. This model system allows us to better understand space filling mechanisms in formulations with the goal of achieving equal performance with the minimum amount of raw materials.
Rheo-optic and rheo-NMR studies of the flow behaviour of wormlike micelles solutions
Allan Raudsepp School of Chemical and Physical Sciences, Victoria University, Wellington, New Zealand
Jeudi 9 septembre 2010 - 14h00 - Amphi Joliot
In the appropriate conditions surfactant molecules in solution may self-assemble into long semi-flexible polymer-like rods called wormlike micelles. Wormlike micelles solutions can show pronounced viscoelasticity and are sometime observed to flow in a peculiar way that suggests that the viscosity of the fluid varies discontinuously. This discontinuous banding has generated considerable interest because of its general implications for the flow behaviour of complex fluids. Despite years of study the underlying mechanism for this flow instability is still not well understood. Here I report on our recent investigations into the flow behaviour of semi-dilute wormlike micelles solutions composed of the surfactant cetylpyridinium chloride (CPCl) and counterion sodium salicylate (NaSal) in brine ([CPCl]/[NaSal]=2, variable weight fraction, in [NaCl]=0.5 M brine) using rheo-optical technique based on homodyne photo-correlation spectroscopy (PCS), diffusing wave spectroscopy (DWS), ellipsometry and direct observation along with rheo-nuclear magnetic resonance (NMR) and conventional mechanical rheometry. Partitioning into stable high viscosity/low shear rate/high birefringence/low turbidity and low viscosity/high shear rate/low birefringence/high turbidity bands was observed in strongly shear-thinning samples in a cylindrical-Couette flow cell geometry using a combination of PCS and ellipsometry. Stable shear banding was also demonstrated in strongly shear thinning samples in the cylindrical-Couette geometry using DWS – DWS measurements suggested that unstable shear flow may be present in the parallel-plate flow geometry. Fluctuating turbid rings were observed directly in strongly shear thinning samples in the parallel-plate geometry – subsequent rheo-NMR measurements indicated that these rings were correlated with formation of a fluctuating high strain band (Fig. 1).
Fig 1. Sequence of transverse rheo-NMR velocity and shear rate images showing shear banding of a wormlike micelles solution in the parallel-plate geometry (r=10 mm, d=0.75 mm).
Tracer diffusion of particles in gels
Taco Nicolai Laboratoire Polymères, Colloïdes, Interfaces - Université du Mans
Jeudi 16 septembre 2010 - Amphi Joliot
We have determined the mean square displacement of spherical particles in globular protein gels using confocal scanning light microscopy. The displacement of particles with different sizes was correlated to the structure of the protein gels. The latter depended strongly on the strength of the electrostatic interactions. In parallel we have studied the diffusion of hard spheres in model particle gels by numerical simulations. The relevance of these simulations to the diffusion of particles in globular protein gels will be discussed.
Surfactant adsorption and formation of microemulsion nanocomposites.
Julien Oberdisse Laboratoire des Colloïdes, Verres et Nanomatériaux - Montpellier
Jeudi 23 septembre - 14h00 Amphi Joliot
Rinse and Repeat : Turning liquids into soft adhesives
Gerald Fuller Chemical Engineering, Stanford University
Jeudi 28 septembre 2010 - 14h00 - amphi Joliot
This paper describes “rinsing flows” wherein a jet of one fluid ablates a layer of a second, miscible liquid that coats a solid substrate. This process is common to everyday experience and to many industrial processes, particularly cleaning operations. This flow arrangement is accompanied by a classic, “hydraulic jump” phenomenon but the stratification of two liquids, with differing rheologies, leads to qualitatively new results. Of particular interest to one of the applications of this process (the cleaning of colloidal particles from solid, planar substrates) is the case when the liquid coating the substrate (the one being rinsed off) possesses a large elongational viscosity. Data are offered that demonstrate that fluids with large, strain thickening extensional viscosities very effectively “pluck” adsorbed colloidal particles from planar surfaces.
Chimie supramoléculaire : un outil de choix pour l’élaboration d’assemblages macromoléculaires multi-stimulables.
Patrice Woisel ENSCL, Lille
jeudi 30 septembre 2010 - Amphi Joliot
