Nacre-like composite films based on mussel-inspired 'glue' and nanoclay

Inspired by the brick-and-mortar structure of nacre and catechol-ferric ion complexes in marine mussel adhesive fibers, we utilized polydopamine (PDA) as super glue and clay nanosheets as bricks to fabricate nacre-like polydopamine-coated clay (D-clay) films using a simple vacuum filtration-assisted assembly method. The D-clay films were subsequently immersed in an aqueous solution of Fe³⁺ ions, allowing Fe³⁺ ions to diffuse in and cross-link the nanosheets. The morphologies and structures of D-clay and D-clay/Fe³⁺ films were characterized using field emission scanning electron microscopy, energy dispersive X-ray element mapping and two-dimensional X-ray diffraction. The results show that the diffusion of Fe³⁺ ions into the D-clay films induces morphological rearrangement of the D-clay platelets, leading to improved alignment and denser packing of the platelets in the films. Synergic combination of the improved packing structure and strong cross-linking coordination bonds result in significantly enhanced mechanical properties for the D-clay/Fe³⁺ films. Moreover, the nacre-like nanocomposite films exhibit excellent fire-shielding properties upon exposure to open flame as PDA can be easily carbonized in the combustion process.