Multiple Dynamic Processes Contribute to the Complex Steady Shear Behavior of Cross-Linked Supramolecular Networks of Semidilute Entangled Polymer Solutions.

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Molecular theories of shear thickening and shear thinning in associative polymer networks are typically united in that they involve a single kinetic parameter that describes the network -- a relaxation time that is related to the lifetime of the associative bonds. Here we report the steady-shear behavior of two structurally identical metallo-supramolecular polymer networks, for which single-relaxation parameter models break down in dramatic fashion. The networks are formed by the addition of reversible cross-linkers to semidilute entangled solutions of PVP in DMSO, and they differ only in the lifetime of the reversible cross-links. Shear thickening is observed for cross-linkers that have a slower dissociation rate (17 s(-1)), while shear thinning is observed for samples that have a faster dissociation rate (ca. 1400 s(-1)). The difference in the steady shear behavior of the unentangled vs. entangled regime reveals an unexpected, additional competing relaxation, ascribed to topological disentanglement in the semidilute entangled regime that contributes to the rheological properties.






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Xu, Donghua, and Stephen L Craig (2010). Multiple Dynamic Processes Contribute to the Complex Steady Shear Behavior of Cross-Linked Supramolecular Networks of Semidilute Entangled Polymer Solutions. J Phys Chem Lett, 1(11). pp. 1683–1686. 10.1021/jz1004818 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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