Self-healing responsive chiral photonic films for sensing and encoding

Abstract

In this work, self-healing chiral photonic films (SCPFs) fabricated by the co-assembly of cellulose nanocrystals (CNCs) with a boronic ester crosslinked poly(vinyl alcohol)–polyacrylamide hydrogel is described. The reversible covalent bonds of boronic esters enable the self-healing of SCPFs, the convenient formation of patterns/stacked structures, and the incorporation of SCPFs onto rough and porous surfaces, addressing a universal method for constructing photonic structures on various substrates. The double layer structures of SCPFs with bulk hydrogels enable multidimensional sensing via dynamic reflectance spectroscopy. The unique dynamic reflectance spectral patterns, as well as regular changes in reflectance maxima and delay time, demonstrate a sensitive photonic sensor. As a result of the self-healing properties, the robust anti-counterfeiting layers formed by the SCPFs on paper-printed QR codes realize polarization-dependent recognitions by a smartphone. The approach allows the incorporation of chiral photonic crystals onto various substrates with high optical quality, providing flexibility to design chiral photonic structures for sensing and security applications.