Phase behavior of diblock copolymer-homopolymer ternary blends with a compositionally asymmetric diblock copolymer

The phase behavior of ternary polymer blends comprising poly(cyclohexylethylene) (C) and polyethylene (E) homopolymers and a compositionally asymmetric CE diblock copolymer rich in C was investigated. Blend morphologies and phase boundaries were established using a combination of optical transmission, small-angle X-ray scattering, and small-angle neutron scattering measurements. The locations of ordered phases are shifted significantly towards lower fractions of C homopolymer, compared to previous results from ternary blends with a symmetric diblock copolymer. Conversely, the Scott line of critical points remains virtually unchanged, coincident with the binary blend critical composition. A central finding is that the line of nearly congruent order-disorder transitions is decoupled in composition from that of the Scott line of critical points. This study demonstrates that diblock copolymer compositional asymmetry significantly impacts the ordered phase regime, but has a marginal effect on the region displaying macroscopic phase separation. It also provides useful guidance for tuning interfacial curvature, a crucial factor in the formation of bicontinuous microemulsions.