Identification of Frank-Kasper Phases in Conformationally Asymmetric Linear Block Copolymer Self-assembly

The quasicrystalline phases which were originally observed in metal alloys have emerged with block copolymers (BCPs) self-assembly providing a new potential in soft materials. Theoretical and experimental studies have revealed that conformational asymmetry (ε) of the different blocks provides a key mechanism to stabilize the Frank-Kasper (FK) σ and A15 phases in BCPs self-assembly. In this work, polydimethylsiloxane-b-poly(2,2,2-triflouroethyl acrylate)s (PDMS-b-PTFEAs) were designed using flexible silicon-containing blocks and rigid fluorine-containing blocks to produce linear BCPs with a high conformational asymmetry. Evaluated value of ε was 2.20 which is higher than other BCPs reported in the literatures. A series of PDMS-b-PTFEAs were synthesized to produce compositionally asymmetric, PDMS-rich phases ranging from f_PDMS = 0.746 to 0.869. Using small-angle X-ray scattering, the FK σ and C14 phases were observed at f_PDMS = 0.80 and 0.85, respectively. Based on the fact that the stability of σ phase increases by the value of ε, we speculate that the stability level of the C14 phase as well as σ phase is due to the relatively high ε of PDMS-b-PTFEAs.