11 research outputs found
Structures statistiques et dynamiques lentes dans les polymères mous. Approches RMN
L’utilisation de la relaxation magnétique transversale des protons, liés aux chaînes, pour la caractérisation des structures statistiques polymères, est illustrée en considérant les gels permanents, les réseaux temporaires d’enchevêtrements dans les hauts polymères fondus et les polymères adsorbés sur les particules minérales. L’approche RMN s’appuie principalement sur l’existence d’une énergie d’intéraction spin-spin résiduelle, résultant de l’anisotropie des mouvements de rotation des unités monomères, anisotropie induite par les contraintes topologiques s’exerçant sur les segments de chaîne
Effects of Retinoic Acid on Airspace Development and Lung Collagen in Hyperoxia-Exposed Newborn Rats
Kinetic analysis of cryotropic gelation of poly(Vinyl Alcohol)/water solutions by small-angle neutron scattering
Aqueous poly(vinyl alcohol) (PVA) solutions subjected to cryogenic treatment form strong physical gels. The cryogenic treatment basically consists of freezing an initially homogeneous polymer solution at low temperatures, storing in the frozen state for a definite time, and defrosting. These gels are of great interest for biotechnology, medicine, the food industry, and many other applications. The outstanding properties of these systems depend on a complex macroporous architecture, whereby PVA chains and water molecules are organized over different hierarchical length scales. The structure and the principal processes subtending the formation of these systems are discussed in the framework of our current understanding of polymer gels. These processes involve formation of ice crystals, PVA crystallization, liquid–liquid phase separation, hydrogen bonding, and entanglements. Small angle neutron scattering is used to follow the cryotropic gelation of PVA/water solutions and detailed information is extracted concerning the gelation mechanism and kinetic parameters related to the formation of these complex systems