Self-assembly of Frank-Kasper Phases in Conformationally Asymmetric Fluorinated Block Copolymers

In recent years, various of Frank-Kasper (FK) phases which were originally observed in metal alloys have been discovered in many soft materials. Theoretical and experimental studies have revealed that conformational asymmetry (ε) of the different blocks provides a key mechanism to stabilize the FK σ and A15 phases between hexagonally packed cylinder (HEX) and body centered cubic (BCC) phases in block copolymers (BCPs) self-assembly. Herein, 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 high conformationally asymmetric BCPs. Evaluated value of ε was 2.20 which is relatively higher than other previously published BCPs. A series of PDMS-b-PTFEAs were synthesized to produce compositionally asymmetric core PTFEA and the corona PDMS blocks. Using small-angle X-ray scattering, the FK σ and C14 phases were observed between HEX and BCC phases. Since 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.