Emergence of Laves Phases in Diblock Copolymer/Homopolymer Blends

Over the past decade, complex particle packings known as Frank-Kasper (FK) phases have been established as fundamental to the phase behavior of compositionally-asymmetric diblock copolymers with low molecular weight and high conformational asymmetry. Laves phases represent a subclass of FK phases, which have only previously been accessed by specific thermal processing protocols. However, recent work with particle-forming surfactant micelles in water indicates that addition of oil to the oleophilic particle cores enables equilibrium Laves phase formation. Inspired by these results, we sought to explore the ability of analogous diblock/core segment homopolymer blends to form similar complex particle packings. Accordingly, we blended a non-FK phase forming polystyrene-block-poly(1,4-butadiene) (SB) diblock copolymer (minority B) with B homopolymers of various molecular weights. Temperature-dependent synchrotron small angle X-ray scattering, and transmission electron microscopy revealed this type of blending indeed breeds complexity in the resulting particle packings, yielding insight into universal geometric principles guiding FK phase formation across soft matter.