Soaking based invisible photonic print with a fast response and high resolution

Abstract

A soaking based invisible photonic print is prepared by regionally selective hydrophobization of SiO₂/PEGMA photonic paper under a mask. The patterns on the prints are invisible in a dry state but visible in water, because the nonuniform swelling behavior of the hydrophilic and hydrophobic regions of the paper induces a different lattice expansion and a large color contrast between the pattern and the background. Due to the uncrosslinked characteristic and the superior swelling ability of the current photonic paper, the invisible patterns printed on it can be reversibly shown and hidden in several seconds and its resolution reaches the micrometer scale, both of which favor its application in antifraud labels or in the identification recognition in our daily lives.