Mechanism of Shear Thickening in Reversibly Cross-Linked Supramolecular Polymer Networks
writer：Donghua Xu, Jennifer L. Hawk, David M. Loveless, Sung Lan Jeon, and Stephen L. Craig*.
keywords：///
source：期刊
specific source：Macromolecules 2010, 43, 3556-3565.
Issue time：2010年
We report here the nonlinear rheological properties of metallo-supramolecular networks formed by the reversible cross-linking of semidilute unentangled solutions of poly(4-vinylpyridine) (PVP) in dimethyl sulfoxide (DMSO). The reversible cross-linkers are bis-Pd(II) or bis-Pt(II) complexes that coordinate to the pyridine functional groups on the PVP. Under steady shear, shear thickening is observed above a critical shear rate, and critical shear rate is experimentally correlated with the lifetime of the metal-ligand bond. The onset and magnitude of the shear thickening depend on the amount of cross-linkers added. In contrast to the behavior observed in most transient networks, the time scale of network relaxation is found to increase during shear thickening. The primary mechanism of shear thickening is ascribed to the shear-induced transformation of intrachain cross-linking to interchain cross-linking, rather than nonlinear high tension along polymer chains that are stretched beyond the Gaussian range.