Sensitivity of Block Copolymer Self-Assembly to the Modification of a Single Monomer

Abstract

In this project, the sensitivity of the phase behaviour of AB diblock copolymers to the addition a single C-monomer is investigated using self-consistent mean-field theory. The reference diblock copolymers are composed of the minority A block with N_A = 12 monomers and the majority B block with N_B monomers. The blocks are mutually repulsive and their interaction is characterised by χ_{ij} and acts over range σ_{ij}, where i and j represent the monomer species. When a C-monomer is added to the junction of the diblock copolymers, we observe a notable shift of the phase boundaries to the larger NB and smaller χ_{AB}. The shift to larger NB is due to an increased polymer stretching. When the C-monomers is nearly-neutral, the shift does not strongly depend on the interaction strength. Similarly, the shift is not visibly affected by changing σ_{AC} and σ_{BC}. However, when the the strength of the interaction is selective such that χ_{AC} = χ_{AB} + α and χ_{BC} = χ_{AB} − α, the shift size decreases with increasing α. Conversely, when the selective C-monomer is added to the majority end, the phase boundaries are shifted to the smaller N_B, with the smallest α giving the largest shift. The shifts can be generically understood to be cause by the interplay between the changes in the interfacial tension and polymer stretching due to the C-monomer. These results demonstrate sensitivity of phase behaviour of AB diblock copolymers to the addition of a C-monomer and may provide a useful link between experiment and theory.