fig7

Figure 7. (A) Depictions of the magnet in air-laid paper and the MPD with varying Fe₃O₄ nanoparticle densities, including schematics, optical views of Fe₃O₄'s spiny shape, and surface images of M-2.0 and M-3.0 post-water wetting, with a 4mm scale bar. (B) Visual transformation of Fe₃O₄'s spiny structure during wetting. (C) Water contact angles on the Fe₃O₄ layer before and after the application. (D) Optical images of prepared M-3.0 showcasing its spiny structure, the loss from finger pressure, and restoration via vibration. Reprinted with permission from ref.^[139]. Copyright 2021 John Wiley & Sons.