I will describe our efforts to understand and design stiffness-changing soft matter with inspirational structure and rheology. Polymer networks and fibrous elastic components are common themes across the three different stories. First, a new design paradigm experimentally realized: soft solid materials that can change stiffness by up to 100 times (10,000%) when exposed to an external stimulus of temperature or magnetic field. Fibrous biopolymer gel networks (fibrin), combined with responsive colloids (polymer microgels or iron particles), enable the dramatic change. Mathematical structure-property models are proposed and tested, explaining the behavior and providing material design guidelines. Second, a study of an inspirational material as yet unmatched by engineering: hagfish slime, an ultrasoft material whose purpose is to clog the gills of predators such as sharks. We have discovered concentration-independent structure and viscoelastic properties, understood with mathematical structure-property models that can support future design of materials. Third, scientific understanding from weakly nonlinear excitations: we have pioneered this technique in rheometry to resolve a 70 year controversy about the mechanism of nonlinear-stiffening in PVA-Borax transient polymer networks. Taken as a whole, this work offers novel ways to understand and achieve stiffness-changing functionality in soft materials.
Speaker: Randy Ewoldt, Univ. of Illinois @ Urbana-Champaign
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