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.
Invisible photonic prints are patterned photonic materials that can reveal hidden patterns under certain stimuli, which are widely used in anti-counterfeiting, identification marking, encoding, and dynamic displays. Traditionally, such photonic prints can be obtained through patterning photonic hydrogels with different responsive polymers. Yet, the visibility of the revealed prints is still not satisfactory due to the limited contrast between the responsive and non-responsive regions. In this study, we report revealable photonic prints with high visibility by patterning photonic hydrogels with two oppositely pH-responsive polymers comprising weak acidic and weak basic groups. The two distinct pH-responsive polymers can be protonated and deprotonated in the same environment, triggering the variation of colors from the initial state to the opposite directions in the different regions of the photonic prints. Therefore, the contrast of the photonic patterns is greatly improved, increasing the naked-eye detection range of colorimetric sensing. This study provides a new opportunity for designing patterned photonic materials for use in improved visual sensors.
危险品化学品经营许可证（带存储）