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The development of cellulose nanocrystal (CNC)-based responsive optical materials with highly durable structure colors has received growing attention. However, stimuli-responsive optical hydrogels with CNCs in chiral nematic arrangements are insufficient for practical applications, due to factors such as their long assembly time and the agglomeration caused by the high percentage of CNCs. Herein, mechano-thermo-chromic hydrogels with uniform interference colors are fabricated by the directional shearing of tunicate cellulose nanocrystals (TCNCs) and subsequent locking of the aligned TCNCs into poly(N-isopropylacrylamide) (PNIPAM) networks. Due to the higher aspect ratio and crystallinity of the TCNCs, iridescence birefringence appeared at a lower concentration. Shear-oriented TCNCs at a moderate concentration (∼5 wt%) not only endow nanocomposite hydrogels with uniform interference colors, but also improve the mechanical properties of the hydrogels. The oriented TCNC/PNIPAM hydrogels display reversible and distinct responsiveness to tensile force, compression, and temperature. This work offers a new strategy to design TCNC-based sustainable and stretchable responsive optical devices for sensors, environmental monitoring, and anti-counterfeiting labels. [ABSTRACT FROM AUTHOR]

Nanocellulose, with its unique optical and chemical properties, has received increasing attention as feedstock to fabricate sustainable materials. However, achieving a nanocellulose-based solvent-free liquid crystal with good responsiveness still remains a challenge. Herein, for the first time, solvent-free supramolecular liquid crystals were fabricated by attaching long side-arms on the fiber-like nanocellulose derived from tunicate (TCNC) with an average width of 20 nm and 400–3000 nm in length. The side-arms were grafted via surface condensation with a charged organosilane, followed by further functionalization with a counter-ion polyoxyethylene ether. The nanoscale liquid crystals consisted of the stiff TCNC as the core and flexible side-arms as the soft shells, forming the core–shell structure with an average width of 34–36 nm. The resulting solvent-free liquid crystal exhibited transparent and viscous liquid-like fluidity, as well as a bright birefringence between the crossed polarizers at room temperature. In our findings, the stiff core provided crystal-like ordering, whereas the soft shells induced the high mobility of the TCNCs as a result of the increased fractional free volume, as shown by positron annihilation lifetime spectra. The unique flowability enables the possibility of multi-responsiveness to temperature, deformation, and alternating electric fields. In addition, the thermo-responsiveness can be regulated by tailoring the canopy. This work provides a novel strategy for the conversion of solid nanocellulose into a solvent-free nanoscale liquid crystal, which is promising for use as a responsive optical material. [ABSTRACT FROM AUTHOR]