Fluctuation stabilization of the Fddd network phase in diblock, triblock, and starblock copolymer melts

Abstract

Self-consistent field theory has demonstrated that the homologous series of (AB)_M starblock copolymers are promising architectures for the complex network Fddd phase. Nevertheless, it remains to be seen if the level of segregation will be sufficient to survive the fluctuations inevitably present in experiments. Here, we study the effect of fluctuations using field-theoretic simulations, which are uniquely capable of evaluating order-order phase transitions. This facilitates the calculation of complete fluctuation-corrected diagrams for the diblock (M=1), symmetric triblock (M=2), and 9-arm starblock (M=9) architectures. Although fluctuations disorder the Fddd phase at weak segregations, they also stabilize the Fddd phase with respect to its ordered neighbors, which extends the Fddd region to higher segregation. Our results provide strong evidence that Fddd will remain stable in experiments on the side of the phase diagram where the outer A blocks of the star form the network domain. However, it is doubtful that Fddd will survive fluctuations on the other side where they form the matrix domain.