Effect of polydispersity on the dynamics, structure, and topology of entangled lamellae forming block copolymers

While essentially all previous simulations of diblock copolymers have studied uniform chain lengths, experimentally, the polymer synthesis always result in a distribution of molecular weights. Here we present molecular dynamics simulations comparing the structure and dynamics of uniform diblock copolymers with those with dispersity in the chain length of one or both blocks. We vary the dispersity in molecular weight near that available experimentally, M_w/M_n = 1.02-1.08. As the dispersity increases, the interfacial width broadens and the average diffusion of the chains parallel to the increases as the increased mobility of the short chains outweighs the decrease in the long chains. A primitive path analysis is used to identify the spatial distribution of entanglements. As the chemical incompatibility between the blocks decreases towards the order disorder transition, the interfacial width is further increased and the spatial distribution of the entanglements changes.