Understanding the structural evolution under the oscillatory shear field to determine the viscoelastic behavior of nanorod filled polymer nanocomposites

Abstract

By taking advantage of the classic coarse-grained molecular dynamics simulation, we have examined the effect of oscillatory shear strain amplitude on the viscoelastic behavior of nanorod (NR) filled polymer nanocomposites (PNCs) by tuning the interfacial interaction between polymer and NRs. We have observed the Payne effect (referred to the nonlinear viscoelastic behavior) at strong interfacial interaction. Payne-effect magnitude gradually increases with the interfacial interaction and the NR volume fraction. To understand the origin of Payne-effect, we examine the NR microstructures and their evolution during the shear field. We find that at low interfacial interaction, the probability of forming NR network is nearly unchanged with the shear strain amplitude; while at strong interfacial interaction, on the contrary the probability significantly decreases with the shear strain amplitude. We infer that various interfacial interactions change the NR network, influencing their evolution behavior under the shear flow. Meanwhile, we calculate the main cluster size and the total number of clusters for the NR network at different shear strain amplitudes, which is consistent with the probability of forming NR network. Thus, the original NR microstructure is significantly broken down under the external shear field, which can also be reflected by the number for polymer-mediated NR network bridged by glassy chains and the connected polymer beads between NRs. In addition, the polymer chains can slip on the filler surface under the shear field. As a result, the observed Payne effect comes from the slippage of the interfacial chains and breakage of the polymer-mediated NR network bridged by glassy chains at strong interfacial interaction. While at low interfacial interaction, it exhibits a weak non-linear behavior. Additionally, both reinforcement and Payne-effect magnitude exhibit a linear dependence on the inverse of the aspect ratio of the NRs. At last, different contributions to reinforcement due to hydrodynamic effects, “occluded rubber”, and “filler network” are quantified where the “filler network” is the main contribution. In summary, this work provides some interesting results to help further understand the relationship between the viscoelastic behavior and the NR network under the shear flow.