Démocratie, diversité, fourniture

Plus de 4 700 participants venus de 165 pays se sont retrouvés en août, à Glasgow, pour la conférence de l’IFLA qui fêtait son 75e anniversaire. Occasion pour Christine Deschamps, présidente, de proclamer « le droit fondamental de chacun à avoir accès à l’information et à pouvoir la diffuser sans restriction aucune.

Scènes de l\u27art en Bavière

Un groupe de bibliothécaires et de documentalistes s’est retrouvé en Bavière pour suivre un programme de visites très dense dans les bibliothèques d’art et de musée à Munich et Nuremberg

Des bibliothèques d’art vues de Florence

L’engouement pour l’Italie qui s’est développé dès le Grand Tour s’est confirmé lors de la rencontre des bibliothécaires d’art à Florence du 19 au 21/10 2009. Cette ville renferme des collections remarquables pour les chercheurs de niveau international. Voici un aperçu de quelques-unes de nos découvertes

Light induced flows opposing drainage in foams and thin-films using photosurfactants

International audienceWe study the influence of UV light on the drainage flows of foams and thin-liquid films stabilized by photoswitchable azobenzene surfactants, whose shape and hydrophobicity can be modified using UV illumination. This model system, the dynamics of which was well characterized in a previous study, enables us to trigger a controlled variation of the surface excess and surface tension. In both geometries we observe light-induced flows which are able to suppress the drainage flow induced by gravity. However, we show that the physical origin of the flows is different in both geometries. At the scale of a few films in the so-called 'two-bubble' experiment the comparisons of the physical length scales, i.e. the radius of the meniscus and the film thickness, to the chemical "reservoir length" (Γ/c) show that the flux of the surfactant at the interface in the presence of UV light is different in the films and in the meniscus, inducing a Marangoni flow from the meniscus to the film, which is stronger than gravity and capillary suction. The velocity of this flow can be tuned by the light intensity and the surfactant concentration. In the real foams, however, we show that the above mechanism is not relevant because the radii of curvature of the Plateau borders are orders of magnitude lower than in the two-bubble experiment, thus the capillary suction prevents such transfer between the films and the Plateau borders. Instead, the decrease of the drainage velocity is shown to be due to a gradient of the surface tension in the illuminated zone hence to a local variation of the capillary pressure. This study underlines the importance of characterizing the radius of the Plateau borders for the understanding of foams, as this key parameter sets the order of magnitude of capillary pressure, film thickness and amount of available surfactant. We also show that this photosurfactant is a new toolbox for the understanding of foam stability

First example of ring carbomer of 1,4-cyclohexadiene

While a series of carbo-mers of 1,3-cyclohexadienes was reported through the use of a specifically developed synthetic strategy, no example of their 1,4-regioisomers was known. Inspired by the methodology elaborated for the preparation of the 1,3-isomers, the synthesis of the first example of carbo-mer of 1,4-cyclohexadiene is presented. Comparison of physico-chemical properties of this first representative with those of the recently described 1,4-regioisomer, especially UV-vis absorption properties, is also addressed