Microphase transitions of block copolymer/nanorod composites under shear flow

Abstract

The shear-induced reorientations and phase transitions of symmetric diblock copolymer/nanorod nanocomposites subjected to steady shear flow, are systematically investigated via dissipative particle dynamics (DPD) simulation method. Both selective and nonselective nanorods (NRs) are considered, with low and high NRs concentrations. To preserve lamellar morphology in the nanocomposites, the NRs concentration is controlled below 15%. The final morphologies of nanocomposites depend on the interplay between NRs and diblock copolymers (DBCPs) under shear flow. The cooperatively induced microphase structures include lamellar (parallel, diagonal and perpendicular alignment), ribbon and cylindrical phases. The presence of anisotropic NRs not only delays or advances the shear-induced transition in lamellae orientation, but also induces the phase transitions by changing the effective composition of the copolymers (f_eff) in nanocomposites. Meanwhile, the low viscosity in the perpendicular lamellae of DBCPs provides an energetic reason for the lamellae changing into perpendicular orientation, with the shear thinning. The shear thinning corresponds to the reorientation of the lamellae, while the shear thickening corresponds to the phase transition from lamellar to ribbon, and to cylindrical structure.