Description:

Title: The Dynamics of Chain Exchange in Block Copolymer Micelles

Abstract: Block copolymers provide a remarkably versatile platform for achieving desired nanostructures by self-assembly, with lengthscales ranging from a few nanometers up to several hundred nanometers. In particular, block copolymer micelles in selective solvents are of great interest across a range of technologies, including drug delivery, imaging, catalysis, lubrication, and extraction. While block copolymers generally adopt the morphologies familiar in small molecule surfactants and lipids (i.e., spherical micelles, worm-like micelles, and vesicles), one key difference is that polymeric micelles are typically not at equilibrium. The primary reason is the large number of repeat units in the insoluble block, Ncore, which makes the thermodynamic penalty for extracting a single chain (“unimer exchange”) substantial. As a consequence, the critical micelle concentration (CMC) is rarely accessed experimentally; however, in the proximity of a critical micelle temperature (CMT), equilibration is possible. We use time-resolved small angle neutron scattering (TR-SANS) to obtain a detailed picture of the mechanisms and time scales for chain exchange, for systems at or near equilibrium. One model system is poly(styrene-b-(ethylene-alt-propylene)) (PS-PEP), in the PEP-selective solvent squalane (C30H62). Equivalent micelles with either normal (hPS) or perdeuterated (dPS) cores are initially mixed in a blend of isotopically substituted squalane, designed to contrast-match a 50:50 hPS:dPS core. Samples are then annealed at a target temperature, and chain exchange is revealed quantitatively by the temporal decay in scattered intensity. A second system consists of poly(n-butyl methacrylate)-b-poly(methyl methacrylate) in immidazolium-based ionic liquids. The dependence of the rate of exchange on all the key variables – concentration, temperature, Ncore, Ncorona, and chain architecture (diblock versus triblock) – will be discussed. 

Tim Lodge graduated from Harvard in 1975 with a B.A. cum laude in Applied Mathematics. He completed his PhD in Chemistry at the University of Wisconsin in 1980, and then spent 20 months as a National Research Council Postdoctoral Fellow at NIST. Since 1982 he has been on the Chemistry faculty at Minnesota, and in 1995 he also became a Professor of Chemical Engineering & Materials Science. In 2013 he was named a Regents Professor, the University’s highest academic rank.

In 1994 he was named a Fellow of the American Physical Society (APS). He received the Arthur K. Doolittle Award from the PMSE Division of the American Chemical Society (ACS) in 1998, and in 2004 he received the APS Polymer Physics Prize. He was elected to Fellowship in the American Association for the Advancement of Science, and he received the International Scientist Award from the Society of Polymer Science, Japan, in 2009. He was the recipient of the 2010 Prize in Polymer Chemistry from the ACS, and was also elected an ACS Fellow in 2010. In 2012 he received the Minnesota Award from the Minnesota Section of the ACS, and the Postbaccalaureate, Graduate and Professional Education Award from the University of Minnesota. He was honored with the Hermann Mark Award of the ACS Division of Polymer Chemistry in 2015, and in 2016 he was elected to the American Academy of Arts and Sciences.

Since 2001 he has been the Editor of the ACS journal Macromolecules. In 2011 he became the founding Editor for ACS Macro Letters. He has served as Chair of the Division of Polymer Physics, APS (1997–8), and as Chair of the Gordon Research Conferences on Colloidal, Macromolecular and Polyelectrolyte Solutions (1998) and Polymer Physics (2000). Since 2005 he has been Director of the NSF-supported Materials Research Science & Engineering Center at Minnesota. He has authored or co-authored over 400 papers in the field of polymer science, and advised or co-advised over 70 PhD students. His research interests center on the structure and dynamics of polymer liquids, including solutions, melts, blends, and block copolymers, with particular emphases on self-assembling systems using rheological, scattering and microscopy techniques.

Description:

Title: Extracting Material Properties from Relaxation Experiments

Abstract: Redox active oxides, with mixed ionic and electronic conductivity (MIEC), are critical components in a wide range of energy technologies, serving as electrodes in fuel cells and batteries, and as reactive substrates in solar-driven thermochemical reactors. Accurate knowledge of the surface reaction rate constant, , is essential for both optimal design of components using existing materials and rational discovery of new materials with enhanced catalytic activity. A variety of relaxation methods have been used extensively to determine . Such approaches rely on the change in some measurable property, most commonly conductivity, upon application of a step change in gas-phase oxygen partial pressure. Under the appropriate experimental conditions, the rate at which the property changes in response to the change in gas-phase oxygen chemical potential provides a direct measure of the material kinetic parameters. Here, we present several considerations relevant to accurate extraction of these parameters, with particular focus on identifying relaxation occurring due to thermodynamic rather than material kinetic reasons. Furthermore, while the electrical conductivity relaxation (ECR) method is one of the most widely employed relaxation techniques because of the ease with which high precision conductivity measurements can be made using samples of almost arbitrary dimensions, ECR is impractical for the evaluation of a material in which the change in conductivity in response to change in oxygen partial pressure is extremely small. For such materials mass relaxation emerges as a viable alternative measurement approach. To this end, we describe a high temperature mass relaxation apparatus based on a gallium phosphate piezocrystal microbalance that enables measurements at temperatures as high 700 °C.

Sossina M. Haile is the Walter P. Murphy Professor of Materials Science and Engineering at Northwestern University, a position she assumed in 2015 after serving 18 years on the faculty at the California Institute of Technology. She earned her Ph.D. in Materials Science and Engineering from the Massachusetts Institute of Technology in 1992. Haile’s research broadly encompasses solid state ionic materials and electrochemical devices, with particular focus on energy technologies. She has established a new class of fuel cells with record performance for clean and efficient electricity generation, and created new avenues for harnessing sunlight to meet rising energy demands. She has published more than 160 articles and holds 12 patents on these and other topics. Amongst her many awards, in 2008 Haile received an American Competitiveness and Innovation (ACI) Fellowship from the U.S. National Science Foundation in recognition of “her timely and transformative research in the energy field and her dedication to inclusive mentoring, education and outreach across many levels.”

Description:

Speaker: Michael Wong, Rice University
Title: Elaborating Heterogeneous Catalysis Concepts for Clean Water

Abstract
One of the central tenets in the field of heterogeneous catalysis is the surface catalytic properties of a material are controlled by its nanostructure. By understanding the structure-property connection at increasingly fine detail, one can create materials to improve our understanding of chemical reactions at the molecular level, and to imbue them with enhanced catalytic performance (i.e., the three S's of speed, selectivity and stability). Through a synthesis-structure-property approach, there is tremendous potential for success in treating recalcitrant water-borne contaminants. To illustrate the developments in this growing genre of heterogeneous catalysis, I discuss several clean-water reaction systems from established and new work from my research program: (1) hydrodechlorination of chlorinated volatible organic compounds using Pd-subshell/Au-core nanostructures and (2) nitrate reduction using In-subshell/Pd-core nanoshapes. These metal-on-metal catalyst offer interesting insights for their respective reactions, i.e., volcano activity dependence on surface coverage.

Biography
Dr. Michael S. Wong is Professor and Chair of the Department of Chemical and Biomolecular Engineering at Rice University. He is also Professor in the Department of Chemistry, Department of Civil and Environmental Engineering, and Department of Materials Science and NanoEngineering. He was educated and trained at Caltech, MIT, and UCSB before arriving at Rice in 2001. His research program broadly addresses chemical engineering problems using the tools of materials chemistry, with a particular interest in energy and environmental applications ("catalysis for clean water") and an emphasis on understanding synthesis-structure-property relationships in heterogeneous catalysis. Current research activities and interests are (i) structure-property analysis of palladium-on-gold catalysts; (ii) metal-on-metal nanoparticle synthesis; (iii) treatment of dioxane, nitrate, fluorocarbons, and chlorocarbons from water; (iv) sugar upgrading chemistry, and (v) nanoparticle assembly.
He has received numerous honors over the years, including the MIT TR35 Young Innovator Award, the American Institute of Chemical Engineers (AIChE) Nanoscale Science and Engineering Young Investigator Award, Smithsonian Magazine Young Innovator Award, Guest Professorship at Dalian Institute of Chemical Physics (DICP), and in 2015, the North American Catalysis Society/Southwest Catalysis Society Excellence in Applied Catalysis Award. He is Research Thrust Leader on 'Multifunctional Nanomaterials" and part of the Leadership Team in the NSF-funded NEWT (Nanotechnology Enabled Water Treatment) Engineering Research Center, based at Rice. He is Chair of the ACS Division of Catalysis Science and Technology (CATL), and serves on the Applied Catalysis B: Environmental editorial board. Previous service includes Chairmanship of the AIChE Nanoscale Science and Engineering Forum and Chemistry of Materials editorial board membership.