Fusion and Fragmentation in Block Copolymer Micelles

Part 1: Non-Technical Summary Micelles are nanoscale objects formed by spontaneous assembly of amphiphilic molecules such as detergents and lipids. Larger amphiphiles known as block copolymers (BCPs) adopt analogous structures but typically are much more robust against mechanical forces or changes in chemical environment. For these reasons, BCP micelles are of growing importance in a variety of emerging technologies, including as viscosity modifiers in synthetic lubricants thereby aiding advanced manufacturing, and for delivery of therapeutic agents to specific target cells, such as cancers, serving as important components in biotechnology applications. In these uses, and many more, the nanostructure is created through the “bottom-up” process of self-assembly, whereby the molecules are carefully designed to produce the intended structure spontaneously. However, a fundamental problem is to understand the mechanisms of self-assembly themselves. In particular, it is desirable to know whether the resulting nanostructure is the most energetically favorable, an equilibrium one, or whether the system has become trapped in a so-called “metastable” state. In the latter case, which is actually quite common, by what mechanisms do micelles evolve toward a more favorable state? With this knowledge, it will be possible to tailor a given advanced manufacturing process to produce the most useful nanostructure, reliably and reproducibly, in the shortest possible time. Graduate students will acquire a broad suite of skills in polymer synthesis and characterization, dynamic light scattering, X-ray scattering, and electron microscopy. They will also have extensive opportunities to present technical talks and posters to external audiences, as well as to mentor talented undergraduates. High school students from the greater Twin Cities will be exposed to polymer science through Polymer Day: You Make It, You Break It, a hands-on component of a broader Discover STEM: Materials Week summer camp. A broad-based cohort of graduate students and postdoctoral fellows from across the country will participate in Future Faculty Workshops, to enhance skills in acquiring and succeeding in academic positions. Part 2: Technical Summary While the equilibrium structure of BCP micelles is relatively well understood, the dynamic processes by which such structures evolve are not. Furthermore, BCP micelles formed by solution self-assembly are often trapped in metastable, non-equilibrium states. A comprehensive experimental program is described, aimed at developing a quantitative understanding of micelle fusion and fragmentation, for which prior studies are very scarce. A suite of powerful experimental tools will be employed, especially dynamic light scattering, small-angle X-ray scattering, and liquid-phase transmission electronic microscopy. The results will provide critical tests of existing models or will provide benchmark data sets to inform future theoretical developments. These studies will be valuable for advanced manufacturing and biotechnology. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2619094 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Timothy Lodge | Institution: University of Minnesota-Twin Cities, MINNEAPOLIS, MN | Award Amount: $569,999 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2619094 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2619094.html