Effect of polydispersity on the self-assembly structure of diblock copolymers under various confined states: A Monte Carlo study

We studied the self-assembly of polydisperse diblock copolymers under various confined states by Monte Carlo simulation. When the copolymers were confined within two parallel walls, it was found that the ordered strip structures appeared alternately with the increase in wall width. Moreover, the wall width at which the ordered structure appeared tended to increase with an increase in the polydispersity index (PDI). On the other hand, the simulation results showed that the copolymers were likely to form ordered concentric strip structures when they were confined within a circle wall. An increase in the PDI led to a change in structure from an ordered concentric strip structure to a newly ordered concentric strip structure. It is interesting to note that one strip was lost while the center was replaced by the other component as the PDI increased. Similar results were obtained in the case of three dimensions. That is, the copolymers were confined in a spherical or cylindrical space. Further along, one layer was lost, and the core was occupied by the other component with the increase in the PDI. We illustrated these phenomena in terms of the frustration between the bulk lamellar repeat period and the confined spacing.