Monte Carlo simulation of the aggregation of rod-flexible triblock copolymers in a thin film

The aggregation of rod-flexible ABA and BAB triblock (A was rod block and repulsive with block B) copolymers in a thin film was studied as a function of varying the rigidity (η) and the length of the rod block by Monte Carlo simulation. The rigidity of block A was defined as η = Rc/Rmax in this study. Rc was the end-to-end distance below which the conformation of the block was not allowed, whereas Rmax was the longest end-to-end distance that the block could be. If η = 0 the block was flexible, whereas if η = 1 the block was a straight rod. The simulation results showed that the ABA triblock copolymer film were likely to form lamella structure with increasing the rigidity (η) of block A. The lamellas were parallel each other and perpendicular to the film surface. However, the aggregation of BAB triblock copolymers tended to change from lamella to cylinder structure with increasing the rigidity (η) of block A. Typical lamella and cylinder co-exist structure was obtained at η = 0.504 for the BAB copolymer film. On the other hand, the simulation results indicated that the film changed from disorder to order, then to disorder structure with increasing the relative length of B block for both ABA and BAB copolymer films. Well ordered lamella for ABA copolymer and well ordered cylinder for BAB copolymer structures could be obtained when the composition of block B is around 50%.