Influence of compositional gradient on the phase behavior of ternary symmetric homopolymer-copolymer blends: A Monte Carlo study

The formation of bicontinuous microemulsions (BUEs) in ternary symmetric blends including two immiscible homopolymers A and B as well as a linear gradient copolymer G is verified by Monte Carlo simulations. Four phase diagrams as a function of segregation strength and blend composition are constructed to show the effects of compositional gradient. Compared with the blends of A/B/diblock copolymers, the BUE phase occupies a broader region in the phase diagram of the A/B/G blends and is replaced by the three-phase coexistence phases of A + B + L or A + B + D at a much lower chain length ratio. Moreover, the lamellar phase is formed at a higher value of segregation strength, has a shorter periodic length and lower orientational order, and spans a narrower range of the phase diagram. A “counteraction effect” is proposed to explain those discrepancies caused by gradient copolymers.