Block copolymer self-assembly is a classic topic in polymer physics. However, over decades, there has been a huge gap between the simple patterns commonly formed by block copolymers and the patterns required for many nanoscale applications. For example, it has been a long-standing problem to fabricate single- or multilayered mesh structures, and all current techniques require tedious layer-by-layer overlays of grating patterns and aligning steps. In this work, we use triblock Janus bottlebrush copolymers (TJBBCPs) as a platform to achieve this goal with a far simpler fabrication process. Their hierarchical self-assembly leads to micro-phase separation along two orthogonal directions: one along backbones forming a lamellar superstructure, and the other normal to backbones forming a nanoconfined substructure within each lamella. With a suitable composition, the substructure gave an unprecedented M15 morphology, which is a mesh-like network structure with a 53° included angle. The M15 substructure is stable only when nanoconfinement is present; otherwise, a gyroid morphology would form instead when the constraint of the lamellar superstructure is removed. Dissipative particle dynamics simulation was carried out to further understand the polymer physics behind the phenomenon, indicating the spatial constraints exerted on the backbone geometry leads to the disappearance of gyroid accompanied by the emergence of M15 in the phase diagram of TJBBCPs.

Emergence of mesh-like network morphologies by nanoconfined hierarchical self-assembly

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