Seminar 11/12/2014 - Daeyeon Lee, University of Pennsylvania: Janus Particles as Solid Surfactants
Abstract: Janus particles are asymmetric colloids with polar and apolar sides. Their amphiphilicity makes this new class of colloids exhibit behaviors that are similar to those of surfactant molecules. The major goal of our work is to address the following intellectual questions: are Janus particles efficient solid surfactants for the stabilization of multiphasic fluid mixtures such as emulsions and foams? And how do their geometry and surface wettability influence their behaviors at fluid interfaces and, in turn, their properties as solid surfactants? In particular, we are inspired by how the chemical composition and shape of molecules influence the surfactant properties of molecular amphiphiles. In this talk, I will discuss our recent work on (1) understanding the effect of particle shape on the configuration and assembly of non-spherical Janus particles at fluid interfaces, (2) the thermodynamics of emulsion stabilization using Janus particles and (3) the emulsion stabilization and phase inversion emulsification using shape-changing/amphiphilicity-reversing Janus particles. I will first show that the configurations of nonspherical Janus particles such as ellipsoids and dumbbells at an oil-water interface strongly depends on the particle characteristics, such as their size, shape, aspect ratio, surface wettability, and the location of the Janus boundary. In the second part of my talk, I will discuss the thermodynamic aspect of emulsion formation using Janus particles. Because the attachment energy of Janus particles to fluid-fluid interfaces is significantly larger than that of homogenous particles, it is possible to generate Pickering emulsions that are thermodynamically stable when Janus particles are used as emulsifiers. In the last part, I will discuss recently developed Janus particles that undergo significant changes in their shape and amphiphilicity in response to changes in the solution pH. We show that it is possible to stabilize different types of emulsions and also induce the phase inversion of emulsions using these stimuli-responsive Janus particles.
Bio: Daeyeon Lee is Associate Professor of Chemical and Biomolecular Engineering at the University of Pennsylvania. Daeyeon received his B.S. in Chemical Engineering from Seoul National University in 2001 and received his Ph.D. in Chemical Engineering/Program in Polymer Science and Technology at MIT in 2007 co-supervised by Robert E. Cohen and Michael F. Rubner. After his Ph.D., Daeyeon was a postdoctoral fellow in the School of Engineering and Applied Sciences at Harvard University where he worked with David A. Weitz. Daeyeon joined the Department of Chemical and Biomolecular Engineering at the University of Pennsylvania in 2009. Daeyeon has won numerous awards and recognitions including the 2010 Victor K. LaMer Award from ACS Colloid and Surface Chemistry Division, the NSF CAREER Award (2011), the 2011 Korean-American Scientists and Engineers Association Young Investigator Award, the 2012 KIChE President Young Investigator Award, the 2013 3M Nontenured Faculty Award, the 2013 AIChE NSEF Young Investigator Award and the 2014 Unilever Young Investigator Award for Outstanding Young Investigator in Colloid and Surfactant Science.
All seminars are held on Wednesdays from 12:00 noon-1:00 p.m. in the Bowen Hall Auditorium Room 222. A light lunch is provided at 11:30 a.m. in the Bowen Hall Atrium immediately prior to the seminar.
Location: Bowen Hall Auditorium
Date/Time: 11/12/14 at 12:00 pm - 11/12/14 at 1:00 pm
Category: PRISM/PCCM Seminar Series