Levich Institute Seminar Announcement, 09/28/2010
Steinman Hall, Room #312
(Chemical Engineering Conference Room)
Professor H. Henning Winter
University of Massachusetts
Department of Chemical Engineering
(Currently on leave with NSF)
"Rheological Study of the Structural Ripening of a Nano-Composite Soft Glass"
Materials in Nature typically gain their functionality from being composite, often on the smallest scale. This is mimicked in manmade nano-composites which profit from the large specific surface area of thin solid enclosures (clay leafs; graphene). However, when manufacturing such nano-composites, most of the structural development is remarkably slow, often occuring in the solid state after having passed through an early liquid-to-solid transition. Such materials are often called "soft glasses" because of their out-of-equilibrium dynamics. Here we examine the slow ripening of an out-of-equilibrium model colloidal solid that consists of clay particles that swell, break up, and eventually exfoliate into randomly oriented clay leafs through the action of end-functionalized ("sticky") polymer molecules. The nano-composite serves as model soft glass in search of regular patterns in the non-equilibrium dynamics in the approach of equilibrium. Experiments show that there exists a stunningly simple pattern in the time-resolved viscoelasticity which can be abstracted as a scaling relation (Macromolecules 43;1901, 2010). Experiments on a wider group of soft glasses is in progress with the objective of confirming or rejecting universality of the novel findings. The experimental protocol includes time-resolved rheometry (Rheol Acta 33:385-397, 1994) and rescaling of data (Rheol Acta 45:331-338, 2006). Acknowledgment: NSF support through CBET-0651888. Collaborators: Xiaoliang Wang, Katie Lania, and Fei Li.
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