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

We report the sensitivity of diblock copolymer particle packing symmetry to the ratio alpha = N-homo/N-core, where N-homo and N-core are the respective homopolymer and core-block degrees of polymerization. Three poly(ethylene oxide)-b-poly(2-ethyllhexyl acrylate) (OA) diblock copolymers with O volume fractions f(O) = 0.15, 0.16, and 0.20 were blended with O homopolymers characterized by alpha = 0.23, 0.42, 0.80, and 1.00. Small-angle X-ray scattering revealed rich phase behavior as a function of alpha, the overall particle core volume fraction (f(core) ), and temperature. BCC, HCP, and Frank-Kasper sigma, C14, C15, and dodecagonal quasicrystal phases, were all identified. "Dry-brush" homopolymer distribution (alpha = 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 (alpha = 0.42) lead to narrow sigma or C15 windows and cylinders at greater O concentrations. Solvent-like swelling (alpha = 0.23) favors widespread a phase formation.