[SY-H11] Linear and non-linear viscoelastic properties of model fractal-like aggregates polymer nanocomposites
Dispersing solid fillers into a polymer matrix is a common strategy to enhance and tailor its properties. Polymer nanocomposites (PNCs) so obtained with fractal-like aggregates have exceptional rheological behavior that have long been exploited in the tire industry. However, due to disparity of time and length scales, our understanding of the relation between nanocomposites structure and rheology remains far from complete.
In this contribution, we propose a mesoscopic model to describe the dynamics and the rheology of aggregate PNCs. While aggregates are described explicitly as groups of interacting particles, we use for the polymer matrix an implicit description based on generalized Langevin equation, that captures the average effect of a viscoelastic medium. These two-level description allows us to simulate large PNCs systems containing dozens of aggregates.
We focus on the linear and non-linear viscoelastic properties of PNCs. We characterize the influence of aggregate size, rigidity and volume fraction. We show that compared to nanoparticles, aggregates may display levels of reinforcement considerably larger. We also demonsrate that the stress relaxation of aggregates display long relaxation times, which originates in the slow rotation of the aggregates. As concerns non linear properties, we concentrate on the Payne effect characterized by a drop of the storage modulus for small deformation amplitudes. We relate the Payne effect to the deformation and alignment of the aggregates under the imposed deformation direction. We also discuss memory effects, and in particular the slow recover kinetics subsequent to a first deformation. All these considerations may help in building connections between the macroscopic mechanical response of the PNCs and the mesoscopic morphology of the nanofillers.
In this contribution, we propose a mesoscopic model to describe the dynamics and the rheology of aggregate PNCs. While aggregates are described explicitly as groups of interacting particles, we use for the polymer matrix an implicit description based on generalized Langevin equation, that captures the average effect of a viscoelastic medium. These two-level description allows us to simulate large PNCs systems containing dozens of aggregates.
We focus on the linear and non-linear viscoelastic properties of PNCs. We characterize the influence of aggregate size, rigidity and volume fraction. We show that compared to nanoparticles, aggregates may display levels of reinforcement considerably larger. We also demonsrate that the stress relaxation of aggregates display long relaxation times, which originates in the slow rotation of the aggregates. As concerns non linear properties, we concentrate on the Payne effect characterized by a drop of the storage modulus for small deformation amplitudes. We relate the Payne effect to the deformation and alignment of the aggregates under the imposed deformation direction. We also discuss memory effects, and in particular the slow recover kinetics subsequent to a first deformation. All these considerations may help in building connections between the macroscopic mechanical response of the PNCs and the mesoscopic morphology of the nanofillers.