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

 Department of Chemical Engineering

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.

 CA, irisoacosta@berkeley.edu