Chemical Engineering Seminar

Block polymers have captured the interest of scientists and engineers for more than half a century. In general, the phase behavior of A-B 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 < fA < 0.25, where fA 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 various 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 a competition between the tendency to form spherical micelles and the constraints associated with filing space at uniform density.