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 chi(AC) between the end blocks is significantly larger than that between the middle and either end block, i.e., chi(AC) > chi(AB) similar to chi(BC). Such systems tend to form ordered structures with no AC interface. Complete phase triangles at fixed values of the products chi N-ij are presented for a model with chi(AB) = chi(BC) < chi(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 chi parameters.