Dynamic Tuning of Optical Transmittance of 1D Colloidal Assemblies of Magnetic Nanostructures

Smart materials with switchable optical properties may find interesting applications in designing advanced intelligent systems. Herein, the dynamic tuning of optical transmission is reported by controlling the orientation of 1D colloidal assemblies of magnetic nanostructures. Colloidal magnetic nanostructures of Fe3O4, including nanospheres, nanorods, and nanodiscs, are assembled into 1D chains under external magnetic fields. Magnetic tuning of the orientation of the nanochains results in a pronounced contrast in optical transmittance, which is strongly dependent on the size and shape of the primary nanostructures. Contrary to the intuitive expectation, the 1D chains of the nanospheres and nanorods exhibit lower transmittance when they are oriented parallel rather than perpendicular to the incident light, whereas the nanodisc counterpart responds oppositely due to the unique “edge‐to‐edge” assembly mode of the nanodiscs. The dynamic tuning of the optical transmittance through magnetic means is believed to have broad applications in the design of novel switchable optical devices. As an example, the incorporation of orientation‐dependent optical properties of 1D chains into the construction of intelligent polymer films with their transparency sensitive to rotation and bending is demonstrated.