Structure and rheological properties of model microemulsion networks filled with nanoparticles

Model microemulsion networks of oil droplets stabilized by non ionic surfactant and telechelic polymer C18-PEO(10k)-C18 have been studied for two droplet-to-polymer size ratios. The rheological properties of the networks have been measured as a function of network connectivity and can be described in terms of simple percolation laws. The network structure has been characterised by Small Angle Neutron Scattering. A Reverse Monte Carlo approach is used to demonstrate the interplay of attraction and repulsion induced by the copolymer. These model networks are then used as matrix for the incorporation of silica nanoparticles (R=10nm), individual dispersion being checked by scattering. A strong impact on the rheological properties is found for silica volume fractions up to 9%

Effect of Nanoparticle Size on the Morphology of Adsorbed Surfactant Layers

The surface aggregates structure of dimethyldodecylamine-N-oxide (C12DAO) in three silica dispersions of different particle sizes (16 - 42 nm) was studied by small-angle neutron scattering (SANS) in a H2O/D2O solvent mixture matching the silica. At the experimental conditions (pH 9) the surfactant exists in its nonionic form and the structure of the adsorbed layer is not affected by added electrolyte. It is found that C12DAO forms spherical surface micelles of 2 nm diameter on the 16 nm silica particles, but oblate ellipsoidal surface micelles are formed on the 27 and 42 nm particles. The dimensions of these oblate surface aggregates (minor and major semi-axes Rn and Rlat) are similar to those of C12DAO micelles in the aqueous solutions. It is concluded that the morphological transition from spherical to ellipsoidal surface aggregates is induced by the surface curvature of the silica particles. A comparison of the shape and dimensions of the surface aggregates formed by C12DAO and C12E5 on the 16 nm silica particles demonstrates that the nature of the surfactant head group does not determine the morphology of the surface aggregates, but has a strong influence on the number of surface aggregates per particle, due to the different interactions of the head groups with the silica surface

Production of shape memory thin strips by twin roll casting technique

Rapid solidification techniques were first used to obtain amorphous or microcrystalline metallic materials, which required high quenching rates (104-106 K.s-1). Applied to shape memory alloys, the twin roll casting technique allows semi-finished materials (strips) with reduced grain size to be obtained. This is particularly useful for certains shape memory alloys for which shaping is difficult because of their inherent lack of ductility. The melt is cast through a nozzle and solidified between the gap of two rollers rotating in opposite directions. Optimum conditions must be established to obtain thin foils with a smooth surface, not brittle and free of cracks and holes. It is only possible for a limited combination of the following experimental parameters : roll speed, melt temperature, melt flow, ejection pressure and roll gap. In this work, we have characterized (transformation temperatures, microstructures) copper based and Ni-Ti-Hf strips, with a thickness between 150 and 500 µm. For copper based alloys, it has been found that transformation temperatures were in a similar range to those of conventionnally cast alloys, which is not the case of melt spun ribbons whose transformation temperatures dramatically decrease. For Ni-Ti-Hf strips cast with different conditions, transformation temperatures vary : some are close to the conventionnally solidified material but some others are lower