Rewritable Photonic Paper with Hygroscopic Salt Solution as Ink



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Flexible photonic paper is fabricated through the instant magnetic assembly of Fe3O4@SiO2 colloids, followed by a rapid photopolymerization to fix the photonic structures inside the PEGDA matrix. Solutions of LiCl, MgCl2, or CaCl2 are used as inks to print durable letters and patterns with color contrast based on the local swelling of the polymer matrix. The photonic paper is rewritable and benign to the environment as the ink marks can simply be removed by washing with water.