Tuning Diblock Copolymer Particle Packing Symmetry with Variable Molecular Weight Core-Homopolymers

Abstract

We report the sensitivity of diblock copolymer particle packing symmetry to the ratio α = Nhomo/Ncore, where Nhomo and Ncore are the respective homopolymer and core-block degrees of polymerization. Three poly(ethylene oxide)-b-poly(2-ethylhexyl acrylate) (OA) diblock copolymers with O volume fractions fO = 0.15, 0.16, and 0.20 were blended with O homopolymers characterized by α = 0.23, 0.42, 0.80, and 1.00. Small-angle X-ray scattering revealed rich phase behavior as a function of α, the overall particle core volume fraction (fcore), and temperature. BCC, HCP, and Frank–Kasper σ, C14, C15, and dodecagonal quasicrystal phases, were all identified. “Dry-brush” homopolymer distribution (α = 0.80 and 1.00) favor C14 and C15 phases with macrophase separation at high homopolymer loadings. “Wet-brush” homopolymer distributions in the particle cores (α = 0.42) lead to narrow σ or C15 windows and cylinders at greater O concentrations. Solvent-like swelling (α = 0.23) favors widespread σ phase formation.