CHE Seminars  

Speaker Prof. Lynn Walker
Department of Chemical Engineering, Carnegie Mellon University, USA
Topic Engineering Fluid-Fluid Interfaces through Multicomponent Adsorption
Date 11,January 2016 (Monday)
Place L-2 Lecture Hall Complex (LHC)
4 pm. - 5 pm.

Dynamic interfacial tension and interfacial rheology measurements are extremely useful for quantifying the adsorption behavior of surfactants, proteins, and polymers at oil/water and air/water interfaces. However, interfacial rheology measurements can be complicated by the presence of bulk surfactant that diffuses to the interface. Species that irreversibly adsorb to an interface allow for the investigation of interfacial behavior without the added complication of surfactant exchange with the bulk. We present a method for generating air/water and oil/water interfaces coated with an irreversibly adsorbed surfactant or protein. The surfactant adsorbs to the interface from a bulk solution for a specified amount of time before the bulk solution is exchanged with deionized water. The amount of surfactant adsorbed on the interface correlates directly with the interfacial tension at the time of rinsing; manipulating the rinsing procedure allows for direct control over the amount of surfactant or protein on the interface. Using a microtensiometer, we then measure the interfacial tension and interfacial rheology of the irreversibly adsorbed layers with no species present in the bulk. We also introduce a second surfactant to the system and observe disruption or displacement of the initial irreversibly adsorbed layer as a function of initial coverage and secondary surfactant concentration. This sequential adsorption procedure allows us to measure the interfacial tension and interfacial rheology of multi-component systems while avoiding bulk interaction. This approach has been applied to polymeric surfactants (Tween), biosurfactants (rhamnolipid) and globular proteins (hydrophobins) and competition with small molecule surfactants.

Lynn M. Walker is a Professor of Chemical Engineering and both Chemistry (by courtesy) and Materials Science & Engineering (by courtesy) at Carnegie Mellon University. She holds a B.S. degree from the University of New Hampshire and a Ph.D. from the University of Delaware, both in chemical engineering. She was an NSF International Postdoctoral Fellow at the Katholieke Universiteit in Leuven, Belgium before joining Carnegie Mellon University in 1997. She spent 2007 as a visiting professor at the Polymer IRC at the University of Leeds in the United Kingdom. Her research focuses on quantifying the coupling between flow behavior and flow-induced microstructure in complex fluids. Current research focuses in two directions; quantifying the influence of flow on self-assembled nanostructures and controlling transport to complex fluid-fluid interfaces. She is the recipient of the DuPont Young Faculty Research Grant and an NSF CAREER award. She has twice been recognized for teaching by receiving the Kun Li Award for Excellence in Education from the Department of Chemical Engineering at Carnegie Mellon University and received the WIC Excellence in Mentoring award in 2015. She currently serves on the editorial boards of the Journal of Rheology and Industrial & Engineering Chemistry Research and the E&PS technical advisory board at Dow Chemical, as well as serving on committees for AIChE and the Society of Rheology.

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