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Distinguished Lecture Series Featuring Dr. Kathleen Stebe

“Curvature Driven Assembly in Soft Matter”

Monday, March 6, 2017


Abstract

Directed assembly is a major tool in materials science. Particles in suspension form structures in response to external fields. The structures can have interesting properties, ranging from electromagnetic responses to mechanical responses. We have been developing new ways to direct assembly in which we exploit confined soft matter to develop energy fields related to the geometry of the confinement.

When a colloid is placed in soft matter, it deforms its host. If the host is a fluid interface, changes in interface area have an energetic consequence. If the host is a liquid crystal, energies from deforming the director field play this role. If the host is a lipid bilayer membrane, costs associated with bending and tension emerge. In each example, by molding the host, we can define global energy fields that drive the colloid along well defined paths to sites for preferred assembly.

We demonstrate this concept in experiment at fluid interfaces by molding their curvatures. Colloids on this interface have excess energy that depends strongly on the local curvature field. Particles move along well defined paths that correspond to principle axes. We extend the concept by confining nematic liquid crystals (NLC) to mold their director fields. In particular, we study colloids in NLC in grooves and near wavy walls. These platforms provide rich landscapes to mold complex assemblies, to study lock and key interactions, and to study multi-stable states. Analogies to electrostatic multipoles interacting with external fields are discussed, and strategies to drive colloids into complex structures are developed.

Biography

Kathleen J. Stebe received a BA in Economics from the City College of New York, Magna cum Laude, and a PhD in Chemical Engineering at the Levich Institute, also at CCNY, under the guidance of Charles Maldarelli. Thereafter, she spent a post-doctoral year in Compiegne, France working with Dominique Barthès Biesel. Professor Stebe joined the Department of Chemical Engineering at Johns Hopkins University, where she rose through the ranks to become Professor and to serve as the department chair. In 2008, Professor Stebe joined the faculty at the University of Pennsylvania as the Richer and Elizabeth M. Goodwin Professor of Engineering and Applied Science. From 2008-2012, Professor Stebe served as the department chair of Chemical and Biomolecular Engineering. In July 2012, she assumed the post of Deputy Dean for Research in the School of Engineering and Applied Science.

Professor Stebe has been a Fellow at the Radcliffe Institute for Advanced Studies; she has received the Robert S. Pond Excellence in Teaching Award at JHU, the Frenkiel Award from the Division of Fluid Dynamics of the American Physical Society, and was named a Fellow of the APS. Professor Stebe’s research focuses on directed assembly in soft matter. Foci include particles interacting by capillarity at interfaces, and particle assembly in complex fluids, including liquid crystals and lipid bilayers. She is an expert in interfacial flows, with particular emphasis on surfactants and Marangoni effects. Other aspects of her research address dynamic surface tension, rheology of protein laden interfaces, and the design of interfaces and bounding surfaces for biological and materials applications.

Professor Stebe is interested in complex fluid interfaces far from equilibrium from a fundamental and engineering viewpoint. In one aspect of her work, she studies the fluid mechanics of surfactant-laden interfaces, dynamic surface tension, wetting phenomena, Marangoni effects, and surfactant-driven anomalous drop break up modes. She is also deeply interested in complex structures which form on fluid interfaces, including protein monolayers and bacterial biofilms. Recently, she has become interested in particle-laden fluid interfaces and how interactions that arise at interfaces can be used to steer particles into well-defined structures. Finally, a major effort in her research group focuses on developing strategies for soft reconfigurable systems by molding director fields and topological defects in confined liquid crystals. Throughout, the Stebe group uses fundamental arguments to develop strategies to direct system behaviors ranging from tip-streaming of droplets from surfactant laden drops to steering particles to well defined locations using capillary energies or liquid crystalline director fields.

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