This present research is performed to study the nonlinear viscoelastic properties of carbon black (CB)-filled polybutadiene/dioctyl sebacate solutions, in which the CB content is fixed while the polymer concentration Φ in the matrix is changed systematically from the coil overlapping state (Φ= Φ*) to the melt state (Φ=1). Our results show that there is a previously unrecognized transition in the system as the matrix polymer concentration Φ approaches and passes through a characteristic polymer concentration Φc. Below Φc, the system typically shows the classic nonlinearity, where storage modulus G’ decreases as strain amplitude γ0 increases and the resulting stress waveforms are distorted from sinusoidal waves. Above Φc, the system displays an anomalous nonlinearity, where the stress responses at any given strain remain surprisingly sinusoidal (or linear) regardless the drop of storage modulus G’. Further, we studied the effect of filler particle size and filler content on this transition. Remarkably, changing the carbon black particle size can significantly change the transition locus, and the characteristic polymer concentration Φc decreases with the increase of the particle size. However, Φc is basically unchanged with the change of CB volume fraction. These results suggest that not only the entanglements of polymer chains but also the mesh size of the entangled network may play important roles in the occurrence of this unusual “dichotomy rheology” in a particle-filled polymer system.

Transition to linear-nonlinear dichotomy in the nonlinear rheology of particle-filled polymer solutions

ACS Fall 2021

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