Transition of Rheological Responses to Linear-Nonlinear Dichotomy: The Role of Polymers in Particle-Filled Solutions

Abstract

We found that the rheological response of particle-filled polymer solutions exhibits an unusual transition under large amplitude oscillatory shears (LAOS). At low polymer concentrations, the system exhibits classic nonlinear behavior, with the storage modulus G′ decreasing as the strain amplitude γ 0 increases, and the stress response is not sinusoidal. However, at high polymer concentrations, the system exhibits anomalous nonlinear behavior, with the stress response to the forced oscillatory shear being surprisingly sinusoidal, while the modulus G′ drops sharply with increasing the strain amplitude γ 0 . We refer to this latter phenomenon as the "linear-nonlinear dichotomy." The characteristic polymer concentration ϕ c at which this transition takes place varies with the type of polymer used in the solution, but for a given filler particle this variation in ϕ c roughly corresponds to a constant polymer entanglement density ρ e in that solution. This discovery suggests that the transition of rheological responses to linear-nonlinear dichotomy in particle-filled polymer solutions is primarily due to the geometric entanglements of polymer chains in the matrix, rather than being influenced by the chemical properties of polymers and filler particles.