Biosynthetic Chiral Nematic Soft Materials with Enhanced Adhesion: Luminescent Adhesives with Universal Adhesions on Hydrophobic and Hydrophilic Surfaces

We present two strategies to achieve excellent adhesive materials based on chiral nematic cellulose nanocrystals (CNC). In the first strategy, we demonstrate crack-free soft monolithic chiral nematic films using the capillary confinement where the increased cohesion is obtained by tailoring hydrogen bonding. To obtain the long-range ordered CNC during a confined drying, we utilized tunicate-inspired hydroxyl group-rich 3,4,5-trihydroxyphenethylamine hydrochloride (TOPA) for hydrogen-bonding. Similarly, physical crosslinking of CNC and polyethylene glycol (PEG) enabled releasing internal stresses at the inner capillary surface. Cross-sectional scanning electron microscopy images revealed that symmetry-breaking occurred with film dried in the capillary tube: transition from the horizontally organized left-handed chiral nematic structure over the wide capillary tube surface to a vertically organized left-handed chiral nematic structure inside of capillary. Overall, we demonstrate a minimal amount of TOPA, 3 wt.%, in the CNC/TOPA/PEG composite enables crack-free monolithic films through enhanced cohesion and adhesion, which improved the mechanical performances, achieved tunable optical bandgap, and enhanced the circular polarization. In the second strategy, chiral nematic CNC and polyelectrolyte complexes enabled universal adhesive properties, including strong adhesion on both hydrophobic and hydrophilic substrates. Furthermore, dynamic and strong photoluminescence with highly asymmetric circularly polarized luminescent is achieved by rare earth europium doping without compromising adhesive strength and original iridescent color. Thus, the unique properties of luminescent soft bio-adhesives with universal adhesion, amplified and switchable photoluminescence, and large and dynamic circularly polarized luminescence can be employed for optical encoding, bio-optical memory, and wearable stickers on human clothes, skins, and gadgets.