The macroscopic properties of a polymer can be tuned by including small inorganic particles, forming a composite. Recently, special attention was given to reducing the particles size towards a nanometric scale, to increase surface contact and amplify the effects on the macroscopic properties of the composite. We developed a model system in which polystyrene-grafted silica nanobeads act as fillers, dispersed in a polystyrene matrix. The grafting of the particles is realized in colloidal solution, by nitroxide-mediated polymerization (NMP) according to a " grafting from " technique. Dispersion of the grafted particles depends on the mass ratio between grafted and free (matrix) chains. Two dispersion types were then observed, by complementary measurements of SAXS and TEM: when matrix mass is close enough to the grafted mass, the silica nanoparticles are homogeneously dispersed as individual particles. To the contrary, when the matrix mass becomes too large compared to the grafted mass, particles gather into dense aggregates. Due to the synthesis of a specific matrix composed of a styrene H/D copolymer, which scattering length density equals that of the silica, we realized a first direct measurement of the grafted chains corona conformation in a polymer melt by SANS. Both silica dispersion and corona conformation were then studied on uniaxially stretched films, to observe their evolution under deformation. Synthesized materials were finally submitted to different mechanical sollicitations (high and small deformations), which responses could be correlated to the local structure of fillers and polymer chains.
