Rational Design of Versatile Self-Assembly Morphology of Rod-Coil Block Copolymer

Controlling the nonlamellar and bicontinuous nanostructures through changing volume fraction is a well-developed technique for coil-coil block copolymer, but it is not always effective for rod-coil block copolymer due to strong rod-rod interaction. Versatile self-assembly morphology of rod-coil copolymer can be achieved by simultaneously adjusting the rod-rod interaction, rod-coil interaction, and conformational asymmetry. This approach has been investigated by using poly(3-alkylthiophene)-b-poly(methyl methacrylate) as a model. By altering the alkyl side chain of polythiophene from linear hexyl to longer dodecyl and to branch 2-ethylhexyl, both rod-coil and rod-rod interaction are decreased with increasing spatial occupation of alkyl side chain which have been quantitatively determined for this type of rod-coil copolymer. With tunable conformational asymmetry, competition between rod-rod and rod-coil interactions, and crystallization driven force, the presence of versatile morphology, i.e, lamellar and hexagonal structures, cylinder-to-gyroid phase transition, and disordered phase, can be observed for long sought composition at approximately f(rod) = 0.5. The finding described here can provide new insights into the self assembly behaviors of rod-coil block copolymer for scientists to manipulate and obtain the desired order morphology in high performance optoelectronic applications.