CHBE 565-Thomas J. Hanratty Lecture, Prof. Timothy P. Lodge, University of Minnesota (Host: Prof. Alexa Kuenstler) "Spontaneous Fission and Fusion of Block Copolymer Micelles"

Abstract:  Block copolymers provide a remarkably versatile platform for achieving desired nanostructures by self-assembly, with dimensions ranging from a few nanometers up to microns. In particular, block copolymer micelles in selective solvents are of 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. This is a result of strong segregation; the length of the core-forming block, coupled to a large interfacial tension, make it difficult for changes to re-arrange once micelles are formed. The kinetic barriers involved can easily approach 100 k_BT.

When micelles are significantly larger or smaller than the equilibrium size, fission and fusion mechanisms, respectively, can become operative. We will describe measurements using dynamic light scattering, small-angle X-ray scattering, and liquid-phase TEM to follow both processes in detail, with some remarkable and unexpected results. For example, the data suggest that fission proceeds through a metastable intermediate state, which is not anticipated by theory. Fusion is “quantized”, in the sense that a population of micelles completely undergoes one fusion event to double the average aggregation number, before a second or third event takes place, suggesting that the rate constant for fusion is a strongly decreasing function of micelle size. In order for fusion to be observed, it is necessary to reduce the steric barrier provided by the corona chains, which can be achieved by systematically reducing the solvent quality for the corona block.

Bio: Tim Lodge graduated from Harvard College with a B.A. cum laude in Applied Mathematics in 1975. He completed his PhD in Chemistry at Wisconsin in 1980 with John Schrag, and then spent 20 months as a National Research Council Postdoctoral Fellow at NIST, with Charles Han. 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 appointed a Regents Professor, the University’s highest academic rank.

Tim Lodge has been recognized with the American Physical Society (APS) Polymer Physics Prize (2004), the International Scientist Award from the Society of Polymer Science, Japan, (2009), the American Chemical Society (ACS) Award in Polymer Chemistry (2010), the Hermann Mark Award (2015) and the Paul Flory Education Award (2018) of the ACS Division of Polymer Chemistry, the Sustained Research Award from the Neutron Scattering Society of America (2020), and the Chemistry of Thermoplastic Elastomers Award, ACS Rubber Division (2026. He has been elected to Fellowship in the American Association for the Advancement of Science, the APS, the ACS, and the Neutron Scattering Society of America. In 2016, he was elected to the American Academy of Arts and Sciences, and in 2024 to the National Academy of Engineering.

From 2001 – 2017, Tim Lodge served as the Editor-in-Chief of the ACS journal Macromolecules. In 2011, he became the founding Editor for ACS Macro Letters. From 2005 – 2022 he was Director of the NSF-funded Materials Research Science & Engineering Center (MRSEC) at Minnesota. He has authored or co-authored over 540 papers in the field of polymer science, and advised or co-advised over 150 PhD students and postdoctoral fellows. 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.