Exploring the Rich Phase Space of Asymmetric Copolymer Blends

Recently, we showed that blending two polystyrene-b-poly(1,4-butadiene) (SB) diblock copolymers can facilitate access to a dodecagonal quasicrystal (QC) as well as Frank-Kasper (FK) σ and A15 phases with massive unit cells (a ≈ 100 nm). Notably, this strategy marked a departure from past work, which, by and large, required both a high degree of architectural asymmetry and low molecular weight to drive similar phase behavior. However, in our past study we only examined the narrow case of a constant length corona block and a variable length core block, leaving unknown the limits of this strategy. In this work, we explore these limits via investigation of a series of SB blends judiciously designed to span the realm of possibilities encountered on blending two SB copolymers. We find using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) that, although a high core block asymmetry yields the largest FK phase stability windows, even a modest increase in the molecular weight distribution, analogous to an increase in the overall dispersity, is sufficient to drive the emergence of these complex packings.