Divergent Shear Thinning and Shear Thickening of Supramolecular Polymer Networks in Semidilute Entangled Polymer Solutions.-Donghua Xu

The steady shear behavior of metallo-supramolecular polymer networks formed by bis-Pd(II) cross-linkers and semidilute entangled solutions of poly(4-vinylpyridine) (PVP) in dimethyl sulfoxide (DMSO) or N,N-dimethylformamide (DMF) is reported. The steady shear behavior of the networks depends on the dissociation rate and association rate of the crosslinkers, the concentration of cross-linkers, and the concentration of the polymer solution. The divergent steady shear behavior—shear thinning versus shear thickening—of samples with identical structure but different cross-linker dynamics [J. Phys. Chem. Lett. 2010, 1, 1683-1686] is further explored in this paper. The divergent steady shear behavior for networks with different cross-linkers is connected to a competition between different time scales: the average time that a cross-linker remains open (τ1) and the local relaxation time of a segment of polymer chain (τsegment). When τ1 is larger than τsegment, shear thickening is observed. When τ1 is smaller than τsegment, only shear thinning is observed.

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