Phase behavior of polymeric microemulsion in ternary A+B+AB blends

Ternary blends of AB diblock copolymers with A and B homopolymers microphase segregate into lamellae (LAM) for copolymer-rich blends and macrophase segregate into A- and B-rich regions for homopolymer-rich blends. Mean-field theory predicts that these regions are separated by three-phase coexistence of the LAM, A-rich, and B-rich phases, which terminates at a Lifshitz critical point. Experiments, however, report that the Lifshitz point is destroyed by fluctuations and that the three-phase coexistence is replaced by a channel of bicontinuous microemulsion (BμE). Using field-theoretic simulations, we show that fluctuations do indeed destroy the Lifshitz point, but that three-phase coexistence continues to exist. However, at high temperatures, the LAM+A+B coexistence predicted by mean-field theory is replaced by BμE+A+B coexistence. We speculate that the single-phase BμE observed in experiments is a result of kinetic trapping as the blend is cooled from the mixed state.