Mechanism of Shear Thickening in Reversibly Cross-linked Supramolecular Polymer Networks.

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We report here the nonlinear rheological properties of metallo-supramolecular networks formed by the reversible cross-linking of semi-dilute 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 that 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.






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Xu, Donghua, Jennifer L Hawk, David M Loveless, Sung Lan Jeon and Stephen L Craig (2010). Mechanism of Shear Thickening in Reversibly Cross-linked Supramolecular Polymer Networks. Macromolecules, 43(7). pp. 3556–3565. 10.1021/ma100093b Retrieved from

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Stephen L Craig

William T. Miller Distinguished Professor of Chemistry

Research interests in Prof. Craig's group bridge physical organic and materials chemistry. Many of these interests are guided by the vision that important challenges in materials science might be better tackled not from the traditional perspective of an engineer, but rather from the molecular perspective of an organic chemist. Current interests include the design and synthesis of self-healing polymers and the use of modern mechanochemistry in new stress-responsive polymers, catalysis, and the study of transition states and reactive intermediates. These areas require an interdisciplinary and nontraditional mix of synthetic organic and polymer chemistry, single-molecule spectroscopy, supramolecular chemistry, and materials characterization. Research interests are complemented by numerous teaching and outreach activities, including: (1) hosting intensive undergraduate and high school research experiences for a diverse group of both Duke and non-Duke students; (2) exploiting effective, scalable, and low-cost mechanisms for content dissemination; (3) team-based and active learning content in the undergraduate and graduate classroom.

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