Emergence of a Metastable Laves C14 Phase of Block Copolymer Micelle Bearing a Glassy Core

Previous studies of the Frank-Kasper (FK) phase of block copolymer (bcp) have highlighted the significance of the mass transfer of constituent molecules in regulating the micelle size to fit in the volume asymmetry of the Voronoi cells comprising the lattice. Here, we present the transformation of a metastable liquidlike packing (LLP) phase into the Laves C14 phase of a conformationally symmetric bcp below the glass-transition temperature of the micelle core (T-g(core)), where the mass transfer during the phase transition was prohibited. The micelles composed of a hard core and a soft corona resembled fuzzy colloids, with their ordering process occurred under the particle number density and size distribution inherited from the LLP phase. We argue that the relatively high size dispersity of the particles drove the hard-core micelles to pack into the C14 phase to relieve the packing frustration of the coronal blocks and the intermicellar repulsion due to the large volume asymmetry and the small surface area, respectively, of the Voronoi cells constituting C14 phase. The present study identified a new regime in which FK phase could emerge from the LLP phase with adequately high polydispersity of particle size even for conformationally symmetric bcp and supported the significance of the LLP structure in directing the ordered packing of bcp micelles.

Automated summary

The study demonstrates that in block copolymers, particles with relatively high size dispersity can drive the micelles to pack into a specific C14 phase, thereby relieving the packing frustration of the Voronoi cells and the intermicellar repulsion due to the volume asymmetry and small surface area of the cells, respectively.