Instability of the microemulsion channel in block copolymer-homopolymer blends

Abstract

Field theoretic simulations are used to predict the equilibrium phase diagram of symmetric blends of AB diblock copolymer with A- and B-type homopolymers. Experiments generally observe a channel of bicontinuous microemulsion (BmE) separating the ordered lamellar (LAM) phase from coexisting homopolymer-rich (A+B) phases. However, our simulations find that the channel is unstable with respect to macrophase separation, in particular, A+B+BmE coexistence at high T and A+B+LAM coexistence at low T. The preference for 3-phase coexistence is attributed to a weak attractive interaction between diblock monolayers