Exploring the Rheological Complexities of Filled Rubbers: Insights into the Linear-Nonlinear Dichotomy

Abstract Under large-amplitude oscillatory shear, filled rubbers usually exhibit a rheological behavior characterized by a linear-nonlinear dichotomy. Specifically, while the amplitude of the stress deviates significantly from the linear dependence on strain, the time-dependent stress response remains linear and sinusoidal. This study seeks to unravel the origin of this complex rheological phenomenon, focusing on the evolution of the linear-nonlinear dichotomy under various dynamic and static strain conditions. Our results reveal that the linear-nonlinear dichotomy in rheological responses of filled rubbers is not due to a mismatch between filler network recovery time and dynamic perturbation time, as commonly believed. We have observed that even at extremely low frequencies (10-5 Hz), which far exceed the typical recovery time frame of the broken filler network in a polymer matrix, there is no sign of a transition in the stress response from sinusoidal to nonsinusoidal behavior. These results challenge the conventional understanding of the dichotomy in filled rubber rheology, suggesting that it is far more complex than previously thought.