SCFT Study of Nonfrustrated ABC Triblock Copolymer Melts

The phase behavior of ABC triblock copolymer melts is studied by self-consistent-field theory (SCFT). We focus on “nonfrustrated” triblocks, in which the Flory−Huggins interaction parameter χ AC between the end blocks is significantly larger than that between the middle and either end block, i.e., χ AC ≫ χ AB ∼ χ BC . Such systems tend to form ordered structures with no AC interface. Complete phase triangles at fixed values of the products χ ij N are presented for a model with χ AB = χ BC ≪ χ AC and for a model with parameters chosen to represent poly(isoprene- b -styrene- b -ethylene oxide) copolymers that have recently been studied experimentally. Particular attention is paid to the structure of the orthorhombic O 70 network phase and the reasons for its existence as well as to the sensitivity of the predicted phase behavior to changes in the χ parameters.