Nonlinear Rheology of Unentangled Polymer Melts Reinforced with High Concentration of Rigid Nanoparticles

A scaling model is presented to analyze the nonlinear rheology of unentangled polymer melts filled with high concentration of small spherical particles. Assuming the majority of chains to be reversibly adsorbed to the surface of the particles, we show that the emergence of nonlinearity in the viscoelastic response of the composite system subjected to a 2D shear flow results from stretching of the adsorbed chains and increasing desorption rate of the adsorbed segments due to the imposed deformation. The steady-state shear viscosity of the mixture in nonlinear shear thinning regime follows the power law η ∼ ɣ̇(-½) where ɣ̇ is the applied shear rate. At large strain amplitude γ(0,) the storage and loss moduli in strain sweep tests scale as G' ∼ ɣ(0)(-1) and G″ ∼ ɣ(0)(-½) respectively.