Phase behavior of diblock copolymer-homopolymer ternary blends containing an asymmetric diblock copolymer*

Lifshitz points (LPs) are predicted to exist in symmetric A/B/A-B ternary blends in the mean-field limit, where A and B are homopolymers and A-B is the corresponding diblock copolymer. At finite molecular weights, the LP is replaced by a channel of bicontinuous microemulsion (BμE) due to fluctuation effects. A recent study of symmetric ternary blends, where A is poly(cyclohexylethylene) (PCHE) and B is poly(ethylene) (PE), demonstrated that the BμE is bracketed by a line of congruent lamellar-disorder transitions and a Scott line of critical points, at homopolymer content near the predicted LP value. In this work, we investigated the phase behavior of a similar PCHE/PE/PCHE-PE ternary blend but with a compositionally asymmetric diblock copolymer. The phase behavior, which was determined using small angle X-ray and neutron scattering and optical transmittance measurements, revealed that the line of congruent transitions is decoupled in composition from the line of critical points. Additionally, a wide range of phase space between the compositions associated with the congruent condition and Scott line was identified as containing the BμE morphology.