Linear-Nonlinear Dichotomy of Rheological Responses in Particle-Filled Polymer Solutions

In this study, we found an anomalous nonlinear behavior under large amplitude oscillatory shears, where the amplitude of stress deviates strongly from the linear dependence of strain, while the time dependence of stress remains sinusoidal. We named this phenomenon as "linear-nonlinear dichotomy", which is usually accompanied with the Payne effect in filled rubbers. In order to understand more molecular details regarding this "dichotomy", we examined a series of oil-extended polyisoprene polymers filled with carbon black. We found that the “dichotomy” emerges from a sharp transition when the mesh size of the entangled polymer network exceeds the diameter of filler particles. The topological structures imposed by the polymer chains on the movement of particles play a key role in the "dichotomy" rheology.