Dynamics of Stress Bearing Particle Networks in Poly(propylene)/Alumina Nanohybrids

In this work, we report about the relationships between the linear rheology and the microstructure of a polymer-nanoparticle model system (i-PP/Al2O3 nanospheres). Over a critical particle volume fraction, rheological evolutions during a quasi-quiescent thermal annealing indicate the formation of a whole-space-spanning transient network of Al2O3 nanospheres, as confirmed by transmission electron microscopy. The dynamics of this network, responsible for the liquid-like to solid-like transition of the nanohybrid, have been investigated by means of rheological measurements. Once the network had formed, the application of large amplitude oscillatory shear progressively and irreversibly destroyed it, leading to a flow-induced structure unable to contribute to the elasticity of the nanohybrid. Conversely, if the large deformation is applied to an unstructured sample, a solid-like feature still emerges by ageing the sample. The resulting strength of such a nanohybrid, however, was lower than that obtainable without the application of large deformations. Energetic considerations may explain the transient nanoparticle network dynamics, strictly related to the bulk rheological properties.