Effects of particle dimension and matrix viscosity on the colloidal aggregation in weakly interacting polymer-nanoparticle composites: a linear viscoelastic analysis

We investigate the relation between structure and viscoelasticity of model polymer nanocomposite systems based on a mixture of spherical nanoparticles and different polymer matrices. When Brownian motions become relevant, the composites exhibit a strong time dependence of the linear visoelastic moduli, which is indicative of the three-dimensional structuring of the filler in the melt polymer. Despite the complexity of the rheological response, we show that the viscoelasticity of the samples can be rationalized by splitting it into the independent responses of the "viscous" suspending polymer melt and that of the "elastic" particle network. Besides underlying the similarities between polymer-based nanocomposites and Newtonian colloidal suspensions, our analysis is expected to be useful for understanding the behavior of other complex fluids where the elasticity of the components may be superimposed.