Nature creates beautiful structural colors, and some of these colors are produced by nanostructural arrays of melanin. Polydopamine (PDA), an artificial black polymer produced by self-oxidative polymerization of dopamine, has attracted extensive attention because of its unique properties. PDA is a melanin-like material, and recent studies have reported that photonic materials based on PDA particles showed structural colors by enhancing color saturation through the absorption of scattered light. Herein, we describe the preparation of three-dimensional (3D) colloidal photonic materials, such as structural color balls and fibers, from biomimetic core-shell particles with melanin-like PDA shell layers. Structural color balls were prepared through the combined use of membrane emulsion and heating. We also demonstrated the use of microfluidic emulsification and solvent diffusion for the fabrication of structural color fibers. The obtained 3D colloidal materials, i.e., balls and fibers, exhibited angle-independent structural colors due to the amorphous assembly of PDA-containing particles. These findings provide new insight for the development of dye-free technology for the coloration of various 3D colloidal architectures.
Holmium (Ho), one of the lanthanide elements, shows a high magnetic moment. Here we present a simple, yet highly potential approach for preparing polymer-based magnetic materials from a three-dimensional polymer network composed with poly(acrylic acid) and Ho showing trivalent nature. We have successfully prepared a magnetic polymer network that reacts directly to a magnet by three-dimensionally immobilizing Ho in the polymer matrix. The present method allowed a preparation of wide range of magnetic materials using polymeric scaffolds, e.g., polymer-grafted particles and cross-linked polymer gels. As a result of the high Ho content, these materials responded quickly to the magnet. The discovery of a method to prepare magnetic materials will provide flexibility in materials design and greatly expand the scope of application of magnetic materials.
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