We present a theory of microphase separation of a diblock copolymer A fN B (1 - f ) N and homopolymer hB blend in the strong segregation limit (χ N ≫ 10), where χ is the Flory−Huggins interaction parameter. Homopolymer chains are assumed to be much longer than block copolymers: N h ≫ N . In this case, homopolymers and diblock copolymers are separated in each elementary cell. We derive a general equation for the free energy and calculate it numerically for different microdomain superstructures: classical lamellar, hexagonal, and body-centered cubic (BCC) structures and also bicontinuous OBDD and gyroid structures. As a result, a phase diagram is constructed in coordinates ( f, φ), where f is the diblock copolymer composition and φ is the volume fraction of the homopolymer in the blend. In particular, we predict a region of stability of one of the bicontinuous phases in the composition window, f = 0.62−0.66.
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Likhtman et al. (1997) studied this question.
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