Invisible Photonic Prints Shown by Deformation

Invisible photonic prints shown by deformation are prepared by soaking the mechanochromic photonic paper with crosslinker (PEGDA) and subsequently crosslinking part of the paper through a photo lithography process. The key point of this new technique is creating patterns and background with very close photonic structures but different mechanochromic capabilities, so that the invisible photonic patterns in relaxed state can be revealed under deformation due to the nonuniform change in photonic structure. Based on the relationship between crosslinking level and the reflection changes during deformation, one can conclude that a low crosslinking level favors the hiding of invisible patterns and a high crosslinking level favors the showing of patterns. The as-prepared samples can instantly and reversibly show the patterns by deformation and hide them by relaxation for many times, and the encapsulation by PDMS rubber prolongs its life time and enhances its durability in practical usages. The current printing technique is capable of creating invisible photonic prints in both macroscale and microscale range, which makes them potentially useful for security and antifraud applications in daily life.