Looking over Liquid Silicone Rubbers: 2. Mechanical properties vs. network topology

International audienceIn the previous paper of this series, eight formulations were analyzed under their un-cross-linked forms to relate Liquid Silicone Rubber (LSR) chemical compositions to material network topologies. Such topologies were confirmed by swelling measurements and hardness evaluation on vulcanized samples. In this article, characterizations of cross-linked materials is further done using different mechanical measurements on final materials, including dynamic mechanical analysis, compression set, stress-strain behavior and tear resistance. It was shown that the compression set value is mainly related to the chains motion: increasing the filler-polymer interactions and/or decreasing the dangling/untethered chains content positively impact the compression resistance. Elongation at break depends on the molar mass between cross-linking points, showing an optimum value set at around 20,000 g.mol-1 i.e. the critical mass between entanglements. The distribution of elastic strands into the network has strong implications on the stress-strain curves profiles. By generating bimodal networks, the ultimate properties are enhanced. The materials cured by hydride addition on vinyl groups catalyzed by peroxide exhibit poorer compression set and tensile strength values, respectively due to post-cross-linking reaction and broad polydispersity index of elastic network chains. A final discussion relates these final mechanical properties to network topologies

Looking over Liquid Silicone Rubbers: (2) Mechanical Properties vs Network Topology

In the previous paper of this series, eight formulations were analyzed under their uncross-linked forms to relate liquid silicone rubber (LSR) chemical compositions to material network topologies. Such topologies were confirmed by swelling measurements and hardness evaluation on vulcanized samples. In this article, characterization of cross-linked materials is further done using different mechanical measurements on final materials, including dynamic mechanical analysis, compression set, stress–strain behavior and tear resistance. It was shown that the compression set value is mainly related to the chains motion: increasing the filler–polymer interactions and/or decreasing the dangling/untethered chains content positively impact the compression resistance. Elongation at break depends on the molar mass between cross-linking points, showing an optimum value set at around 20 000 g mol^–1, i.e., the critical mass between entanglements. The distribution of elastic strands into the network has strong implications on the stress–strain curves profiles. By generating bimodal networks, the ultimate properties are enhanced. The materials cured by hydride addition on vinyl groups catalyzed by peroxide exhibit poorer compression set and tensile strength values, respectively, because of post-cross-linking reaction and broad polydispersity index of elastic network chains

Le conte dans tous ses états

De l’engouement né des volumes de Perrault ou des Grimm à aujourd’hui, l’attrait pour le conte ne s’est jamais démenti : parce que celui-ci invite à l’émerveillement, il a donné lieu à réécritures enjouées, adaptations admiratives, mais aussi interrogations et subversions démystifiantes. Toutefois, la critique, le déplacement dans un autre genre – récit filmique, photographie, notamment – ne sont pas déliaison mais réaffirmation du lien qui nous attache à cette énigme toujours renouvelée qu’est le conte – et avec lui le plaisir que nous y trouvons. Ce volume, généreusement illustré par la photographe Dina Goldstein et dirigé par Florence Fix (université Rouen- Normandie) et Hermeline Pernoud (université Paris 3-Sorbonne Nouvelle), réunit quinze textes analysant la permanence du conte dans la modernité : un conte dans tous ses états, malmené, adapté, raillé, déplacé, mais toujours vivace et propice à un réenchantement de la lecture