Claude Simon

Deux souvenirs, parmi d’autres : - En 1973, Maurice Schumann, ministre des Affaires étrangères, me demande, après l’attribution du Prix Nobel à Samuel Beckett, les noms de deux écrivains français qui auraient pu et pourraient être lauréats. Compte tenu des critères particuliers, plausibles des choix de l’Académie suédoise, je cite Nathalie Sarraute et Claude Simon. Le ministère des Affaires étrangères où je fus responsable des missions culturelles, s’honore d’avoir souvent aidé ces deux géant..

Claude Simon

Deux souvenirs, parmi d’autres : - En 1973, Maurice Schumann, ministre des Affaires étrangères, me demande, après l’attribution du Prix Nobel à Samuel Beckett, les noms de deux écrivains français qui auraient pu et pourraient être lauréats. Compte tenu des critères particuliers, plausibles des choix de l’Académie suédoise, je cite Nathalie Sarraute et Claude Simon. Le ministère des Affaires étrangères où je fus responsable des missions culturelles, s’honore d’avoir souvent aidé ces deux géant..

Polymer brush collapse under shear flow

Shear responsive surfaces offer potential advances in a number of applications. Surface functionalisation using polymer brushes is one route to such properties, particularly in the case of entangled polymers. We report on neutron reflectometry measurements of polymer brushes in entangled polymer solutions performed under controlled shear, as well as coarse-grained computer simulations corresponding to these interfaces. Here we show a reversible and reproducible collapse of the brushes, increasing with the shear rate. Using two brushes of greatly different chain lengths and grafting densities, we demonstrate that the dynamics responsible for the structural change of the brush are governed by the free chains in solution rather than the brush itself, within the range of parameters examined. The phenomenon of the brush collapse could find applications in the tailoring of nanosensors, and as a way to dynamically control surface friction and adhesion

Slip and friction mechanisms at polymer semi-dilute solutions / solid interfaces

The role of the polymer volume fraction, $\phi$, on steady state slippage and interfacial friction is investigated for a semi-dilute polystyrene solutions in diethyl phthalate in contact with two solid surfaces. Signicant slippage is evidenced for all samples, with slip lengths b obeying a power law dependence. The Navier's interfacial friction coecient, k, is deduced from the slip length measurements and from independent measurements of the solutions viscosity $\eta$. The observed scaling of k versus $\phi$ clearly excludes a molecular mechanism of friction based on the existence of a depletion layer. Instead, we show that the data of $\eta$($\phi$) and k($\phi$) are understood when taking into account the dependence of the solvent friction on $\phi$. Two models, based on the friction of blobs or of monomers on the solid surface, well describe our data. Both points out that the Navier's interfacial friction is a semi-local phenomenon

Gum Arabic in solution: Composition and multi-scale structures

Gum Arabic is a natural acacia tree exudate containing hyperbranched polysaccharides and proteins. Here, we perform a dual chromatographic separation together with small-angle X-ray and neutron scattering structural characterizations. We show that the different species present in Gum Arabic can not be easily classified in distinct families. They are rather build from various combinations of two building blocks that are evidenced by a mismatch between small-angle X-ray and neutron scattering. One block corresponds to hyperbranched polysaccharides, which we describe as three-dimensional multi-scale porous colloids possessing three length scales of 7, 2 and 0.7 nm. The other block corresponds to protein chains that organize as Gaussian chains in solution and are prone to aggregation. A large array of polysaccharide/protein conjugates was identified, which differs in size, hydrophobicity and amino-acid content. Still, their structure is always the juxtaposition of the two building blocks structures. Additionally, small-angle neutron scattering reveals that large-scale structures are ubiquitous in Gum Arabic solutions and originate from the self-association of both free and conjugated polypeptide chains. Despite its compositional complexity, Gum Arabic solutions thus possess a robust multi-scale structure that is mainly impacted by concentration and ionic repulsions

Edouard Chennevière : témoignage

National audienc

Neutron reflectivity for soft matter

Specular neutron reflectivity is a technique enabling the measurement of coherent neutron scattering length density profile perpendicular to the plane of a surface or interface, and thereby the profile of chemical composition. The characteristic sizes that are probed range from around 5Å up 5000 Å. It is a scattering technique that averages information over the entire surface and it is therefore not possible to obtain information on correlations in the plane of the interface. The specific properties of neutrons (possibility of tuning the contrast by isotopic substitution, negligible absorption, low energy of the incident neutrons) makes it particularly interesting in the fields of soft matter and biophysics. This course is composed of three parts describing respectively its principle, the experimental aspects (diffractometers, samples), and some scientific examples of neutron reflectometry focusing on the use of contrast variation to probe polymeric systems

Edouard Chennevière : témoignage

National audienc

Détrônement du principe du contradictoire : tout n’est pas permis en expertise médicale !

La décision commentée circonscrit avec justesse les pourtours du principe du contradictoire en matière d’expertise médicale. En particulier, saisi sur pied de l’article 973 du Code judiciaire dans le cadre d’un litige résultant d’un accident de travail, le Tribunal du travail francophone de Bruxelles s’est prononcé sur une problématique croissante dans le domaine expertal belge : le débiteur de la réparation du préjudice impose la présence de son conseil technique, en l’espèce spécialisé en psychiatrie, à l’expertise du sapiteur psychiatrique désigné par l’expert judiciaire