Characterizing the structure of the disordered micellar regime of asymmetric diblock copolymers using simulations

Experiments on highly asymmetric diblock copolymers have revealed that disordered micelles exist above the order-disorder transition temperature. Self-consistent field theory is incapable of describing this disordered micellar state. In this work, we perform molecular dynamics simulations of a coarse-grained model to study the disordered micellar state of asymmetric diblock copolymers with a minority block volume fraction of 0.125. We characterize the structure of these disordered micelles in reciprocal space by measuring the structure factor and in real space by identifying clusters rich in the minority block type. Near the order-disorder transition, the structure factor exhibits a secondary shoulder at high wave numbers similar to that seen in experiments, which has been interpreted as arising from correlations in the positions of disordered micelles. Direct analysis of configurations shows the existence of micelle-like clusters at segregation strengths well below those at which they become apparent from the appearance of this feature in the structure factor.