Modeling the flow-driven disassembly and extensional rheology of end-linking telechelic polymers

Abstract

End-linking telechelic polymers can self-assemble into supramolecular chains that act as high-molecular-weight viscosity modifiers in linear response, but disassemble rather than degrade in nonlinear flows. We use coarse-grained molecular dynamics to simulate the nonequilibrium dynamics of end-linking linear telechelic polymers with bivalent associations during nonlinear elongational flows. Steady state flow curves reveal a near-perfect rate-thinning of the steady state extensional viscosity ηE∼ε̇−1, which coincides with a plateau in the steady-state extensional stress σE. This stress plateau coincides with an unexpected decrease in average chain extension with increasing strain rate, which arises from enhanced stretch fluctuations driven by flow-induced bond dissociation and reformation. Flow drives the disassembly of large supramolecular chains, but the distribution of supramolecular weights remains exponentially distributed. The average molecular weight of supramolecular chains decreases with increasing rate with ⟨Mc⟩∼ε̇−1/2, resulting in diffusive scaling of the extensional viscosity, with the average supramolecule size ηE∼⟨Mc⟩2.