(742g) Polytypism of Close-Packed Block Copolymer Micelles By Temperature Quenching | AIChE

(742g) Polytypism of Close-Packed Block Copolymer Micelles By Temperature Quenching


Lee, S. - Presenter, Rensselaer Polytechnic Institute
Chen, L., Rensselaer Polytechnic Institute
Lee, H., University of Minnesota
We investigated the close-packed structures of strongly-segregated block copolymer micelles in water
induced by temperature quenching. We found that the polytypes of close-packed block copolymer micelles
could be induced from a disordered state at an elevated temperature by changing the depth of quench. As a
function of quench depth, the quenched self-assembled block copolymer micelles formed three different
close-packed structures: face-centered cubic (FCC), random stacking of hexagonal-close packed layers
(RHCP), and hexagonal-close-packed (HCP). The induced HCP and RHCP structures were stable for at least
a few weeks when maintained at their quench temperatures, but heating or cooling these HCP and RHCP
structures transformed both structures to FCC crystallites with coarsening of the crystal grains, which
suggests that these non-cubic close-packed structures are intermediate states. We believe that the long-lived
metastable HCP and RHCP structures originate from the small size of crystal grains, which introduces a nonnegligible
Laplace pressure to the crystal domains that stabilize the intermediate structures. This finding
suggests that the size of crystalline domains influence the stability of crystalline structures and shows the
importance of the morphology of crystalline structures to the polymorphism of materials.