Morphological Transitions and Chain Conformations in AB2 Miktoarm Star Block Copolymers: A Molecular Dynamics Study

Abstract

This study investigates the role of chain architecture and block asymmetry on the morphology of AB₂ miktoarm star block copolymers (AB₂ BCPs) in the strongly segregated regime using molecular dynamics simulations. Notably, the cylindrical morphology in AB₂ BCPs persists across a broad compositional range, extending close to f_A ≈ 0.5, in agreement with both theoretical and experimental findings. The lamellar morphology observed up to f_A ≈ 0.8 matches predictions; however, beyond this point, AB₂ BCPs continue to exhibit lamellar structures (disk-like micelles), deviating from the expected transitions to cylindrical or spherical morphologies. This behavior, corroborated by dissipative particle dynamics simulations, is attributed to the B arms’ preference to occupying the outer regions of curved interfaces, which hinders the formation of cylindrical or spherical morphologies. Furthermore, domain spacing results exhibit remarkable agreement with strong-stretching theory (SST) across different morphologies, reinforcing the predictive power of SST. Finally, shape parameter analysis, including metrics like asphericity and acylindricity, underscores the significant impact of chain architecture on these morphological transitions. These findings provide molecular-level insights into how chain architecture and block asymmetry dictate phase behavior and morphological stability in linear and miktoarm BCPs.