Filler structure and segmental dynamics in polymer nanocomposites
Résumé
Polymer nanocomposites are mixtures of nanoparticles and polymer chains, where the filler particles are usually added to enhance mechanical properties, e.g. of car tire materials. Performance depends to a great extent on the structure of the filler, i.e. its dispersion state in the polymer matrix, which itself depends on mixing protocols, but also on the thermodynamics of the system. The latter can be tuned by performing either chemical surface modifications of the nanoparticles, or by playing with the mass and/or grafting properties of the polymer chains.
Some straightforward ways to obtain information from small-angle scattering on the filler structure of nanocomposites will be presented. In particular, we recently developed a quantitative analysis of the scattered intensity in the intermediate q range. It is based on the similarity in local structure between infinitely large homogeneous assemblies of hard spheres or moderately sticky hard spheres with any finite-sized nanoparticle assembly dominated by hard sphere interactions. This method provides direct information on the local volume fraction of particles. It will then be applied to the impact of small molecules on the silica structure in nanocomposites close to industrial applications.
Finally, a second issue for the mechanical response of nanocomposites relates to the polymer dynamics, which may also be governed by the filler dispersion. We will present first quasi-elastic neutron scattering results showing the impact of the aggregation state on the segmental dynamics of the same samples by means of incoherent neutron spin-echo.