Brownian molecular dynamics simulation on self-assembly behavior of diblock copolymers: influence of chain conformation.

Brownian molecular dynamic simulations are applied on the self-assembly behavior of AB-type diblock copolymers. The influence of chain conformation of core-forming A-block changing from rigid to flexible on the aggregation structure formed by AB copolymers is investigated. It is found that at a high rigid fraction f(R) of A-block, a disk structure can be formed at a high aggregation interaction epsilon(AA) of A-bead pairs because of the tendency of orientational packing of rigid portion within the aggregate core. Transitions of aggregation structure from disk to string, further to small aggregates, and to unimers are observed with decreasing epsilon(AA). The packing of A-blocks becomes more random at relatively lower values of f(R), resulting in the formation of spherical structure. The region of string becomes narrower while the regions of the small aggregates and sphere become wider as decreasing f(R). Meanwhile, the onsets of string, disk, and sphere formation move to higher epsilon(AA). The phase diagrams for the influences of rigid potion location within the A-block and the chain rigidity of the A-block are mapped. The comparison of simulation results with existing experimental observations is also presented. Our simulation results tend to bridge a gap of different micellization behaviors between rod-coil block copolymers and coil-coil block copolymers and extend to investigate chain conformation influence on phase diagram.