Ultraviolet-magnetic response multicolored janus colloidal photonic crystal beads for information coding

We report a new kind of ultraviolet (UV)-magnetic response Janus colloidal photonic crystal (CPC) beads for information coding. The Janus beads made up of fluorescent CPCs and Fe3O4 nanoparticles show different colors under visible light, UV light and magnetic stimulation. In the concrete scheme, monodisperse colloidal particles with and without fluorescent molecule SPMA were prepared by semi-continuous emulsion polymerization. Then colloidal particles and Fe3O4 nanoparticles were paired as precursors to prepare Janus beads by the droplet template method. During the slow self-assembly process, Fe3O4 nanoparticles were deposited on the bottom and colloidal particles filled the other parts of the beads so that a Janus structure formed. Therefore, the upper surface of Janus beads appears structural color and the lower surface appears black. The variation of Fe content in different hemispheres allows the controllable magnetic response to reverse the beads. The presence of fluorescent molecule SPMA makes fluorescent Janus beads (FJBs) emit fluorescence under UV light. According to design, an array in a particular arrangement of Janus beads can realize reversible changes between three different optical information. Furthermore, the binary cipher was combined with Janus beads to design and fabricate an optical encoding array, revealing an important application in information coding.