Magnetoresponsive Cellulose Nanofiber Hydrogels: Dynamic Structuring, Selective Light Transmission, and Information Encoding

Angle-dependent light reflection is a common phenomenon in nature, typically arising from the spatial arrangement of biological or mineral structures. Various strategies have been developed to replicate these assemblies, particularly to achieve structural color through bottom-up self- and directed assembly. However, dynamic control of light reflection remains a significant challenge. In this study, we present TEMPO-oxidized cellulose nanofibers modified with magnetic nanoparticles (approximately 10 nm in size) that exhibit rapid, directional alignment in aqueous media under magnetic fields, resulting in angle-dependent light reflection. By combining magnetic field manipulation with gas-phase hydrogelation, we were able to arrest the hydrogel structure, preserving the nanofibers' spatial and temporal orientation. This system enables the creation of on-demand optical patterns, which we demonstrate through selective light transmission and reflection, offering potential for applications in information coding, storage, and encryption.