In Situ Control of Self-Assembled Morphology and Photonic Properties via In-Film Polymerization

Bottlebrush block copolymers (BBCPs) are promising materials for the fabrication of photonic crystals because of their tunable composition and rapid self-assembly into large-period nanostructures. However, it is currently difficult to achieve spatially resolved control over nanostructure and photonic response, because these nanostructures are usually fixed upon fabrication. Here, we demonstrate that in-film polymerization within a BBCP photonic film provides a composition-directing route to alter its morphology and structural color based on the effective volume fraction of the two blocks. Monomer vapor swells photoinitiator-containing BBCP films and undergoes UV-triggered photopolymerization, generating a homopolymer in situ within the BBCP matrix. Reflectance spectroscopy monitored the color evolution, while SEM visualized the accompanying morphology changes, which were driven by the shift in film composition from the resulting homopolymer. Masked irradiation further provides a proof-of-concept route to localize the polymerization and resulting optical response within a single film.