Network Phase with Frank-Kasper-Like Symmetry from Controlled Self-Assembly of High-χ Star-Block Copolymers

Network phases can be obtained by using PS-selective solvent for controlled self-assembly of high-χ lamellae-forming polystyrene-block-polydimethylsiloxane (PS-b-PDMS) block copolymers. By taking advantage of the topology effect on BCP self-assembly, network phases with higher packing frustration can be obtained. With the combined effect of high χ and molecular topology, apart from double gyroid (trigonal planar structure) and double diamond (tetrahedral structure or tetrapod), a unique network phase with double networks of PDMS in PS matrix but mixed trigonal and crossing structure can be found as evidenced in reconstruction images by electron tomography. Most interestingly, the small angle X-ray scattering result give the profile same as the A15 phase, one of Frank-Kasper phases, with space group of Pm3n. The observed phase behaviors might provide the conceptual ideas for the development of network phase from FK phase via space filling to decipher the origins of the complex network phases due to the character of malleable mesoatoms (i.e., microphase-separated domains) that gives the adaptation with complex curvatures.