ChBE Seminar Series - Cary Lecture: Frank S. Bates
In addition to its annual lectures, ChBE hosts a weekly seminar throughout the year with invited lecturers who are prominent in their fields. Unless otherwise noted, all seminars are held on Wednesdays in the Molecular Science and Engineering Building ("M" Building) in G011 (Cherry Logan Emerson Lecture Theater) at 4 p.m. Refreshments are served at 3:30 p.m. in the Emerson-Lewis Reception Salon.
Frank S. Bates, University of Minnesota
Frank S. Bates, a Regents professor at the University of Minnesota, will give the 32nd Ashton Cary Lecture at 4 p.m. March 1 in the MoSE Building (Room G011). His talk is titled “Sphericity and Symmetry Breaking in the Formation of Quasicrystals and Frank-Kasper Phases in Block Polymer Melts.” A reception will follow in MoSE Atrium 2.
Bates will also give a special lecture – “Toughened Thermoset Epoxy Plastics” – at 11 a.m. on March 2 in L1255 of Ford ES&T (with a reception at 10:30 a.m. in the L1 atrium).
March 1 Lecture:
“Sphericity and Symmetry Breaking in the Formation of Quasicrystals and Frank-Kasper Phases in Block Polymer Melts”
Spherical objects ranging in size from metal atoms to micron scale colloidal particles to billiard balls tend to form regular close packed arrays with three-dimensional translational symmetry. This lecture will describe how nearly spherical nanoscale micelles, formed by self-assembled diblock copolymers, spontaneously evolve into a 2-dimensional dodecagonal quasicrystal (DDQC) following rapid cooling from the disordered liquid state. This aperiodic arrangement, characterized by rotational symmetry but not translational symmetry, transforms over time into a 3-dimensional Frank-Kasper (FK) phase with local tetrahedral particle packing. This discovery suggests that certain forms of quasicrystalline order are non-equilibrium states generated by kinetically facilitated particle clustering in the supercooled liquid. Redistribution of polymer molecules between micelles through molecular diffusion appears to play a central role in these processes. Surprising analogies will be drawn between the heretofore unexplained formation of FK structures in soft materials, and in certain elemental metals (including manganese and uranium) and alloys, highlighting opportunities to better understand space filling in hard and soft materials by investigation of block polymers with precisely tuned molecular architectures.
March 2 Lecture:
“Toughened Thermoset Epoxy Plastics”
Block copolymers belong to a broad class of amphiphilic compounds that includes soaps, lipids and nonionic surfactants. These macromolecules assemble into micelles with molecular dimensions on the order of 5 to 50 nm in size when mixed with excess solvent that preferentially solvates one block type. This presentation will explore block copolymer micelle formation in commercial thermoset epoxy resins and the fundamental mechanisms that lead to fracture toughness in the thermally cured products. In-situ synchrotron small-angle x-ray scattering has confirmed cooperative cavitation of nanoscale rubbery micelles that triggers shear yielding as the energy absorbing mechanism that imparts extraordinary toughness without sacrificing stiffness or use temperature. Recent generalization of these concepts to complex epoxy formulations and the synergistic use of graphene and block copolymer micelles, resulting in a 20-fold increase in the strain-energy release rate over the neat plastic, will be described.