Right-Handed Chiral Photonic Cellulose Nanocrystal Films

Chirality transfer across length scales is a fascinating phenomenon that has intrigued researchers across disciplines. This is especially the case with cellulose, where, despite being one of the most exploited materials in our society, such as paper and cotton, it remains elusive when it comes to the transfer of intrinsic chirality at the molecular scale to larger hierarchical structures. Here, we show that in the case of cellulose nanocrystals (CNCs), allomorphic transformation from cellulose I to cellulose II can lead to chirality inversions in chiral nematic suspensions. This phenomenon allows the fabrication of right-handed chiral photonic films using CNCs extracted from standard plant biomass, which is first mercerized and then subjected to sulfuric acid hydrolysis, followed by desulfation. Similar to standard cellulose I-based CNC self-assembly, the twist chirality and aspect ratio of the left-handed CNCs in cellulose II can be significantly modified through crystallite aggregation engineering. In contrast to molecular liquid crystals, chirality inversion has never been presented in colloidal liquid crystals, and our findings present a step toward the development of so far inaccessible cellulose materials beyond the native crystallinity.