Ice-nine and the Origins of Frank-Kasper and Quasicrystal Phases in Diblock Copolymer Melts
Colloquium | January 24 | 4-6 p.m. | 180 Tan Hall
Frank Bates, University of Minnesota
Block polymers have captured the interest of scientists and engineers for more than half a century. In general, the phase behavior of diblock copolymers, the simplest category of such self-assembling macromolecules, has been accepted as thoroughly understood. Recent experiments with low molecular weight diblock copolymers have revealed remarkable phase complexity in the limit of asymmetric compositions, 0.15 < fx < 0.25, where fx signifies the volume fraction of the minority block. Small-angle x-ray scattering (SAXS) measurements conducted in the vicinity of the order-disorder transition (ODT) temperature have revealed the formation of several low symmetry Frank-Kasper phases and a dodecagonal quasicrystal as a function of thermal processing history. Remarkably, when heated above the ODT temperature the liquid micelles retain a memory of the ordered state, which returns upon cooling. These finding will be discussed in the context of the occurrence of low symmetry crystals in soft and hard materials.