Decoding the Conditions for Aperiodicity in Complex Diblock Micelle Packings via Breakout Crystallization

Over the past decade it has been well documented that bulk particle forming diblock copolymer melts will often self-assemble into a metastable dodecagonal quasicrystal (DDQC), possessing crystallographically forbidden 12-fold rotational symmetry, en route to equilibrium Frank–Kasper phases. The conditions for this behavior, however, remain obscure. To this end we designed a crystalline amorphous poly(ethylene oxide)-block-poly(2-ethyl hexylacrylate) diblock copolymer that undergoes breakout crystallization. Melting the semicrystalline state enabled direct access to a supercooled liquid-like packing (LLP) of particles far below the melt order-disorder transition temperature. Critically, this mode of access to the LLP state purely on heating avoids unwanted phase nucleation associated with traversing higher temperature regions of the phase space. Extensive temperature-dependent synchrotron small angle X-ray scattering demonstrated that this pure LLP state alone gives rise to the DDQC– avoiding any nucleation of the high-temperature body centered cubic particle packing. Accordingly, we cast the DDQC as an Ostwald-step between LLP and the equilibrium Frank-Kasper σ phase, representing the kinetically favored diblock particle packing polymorph when growing σ from LLP.