Multidimensional dynamic regulation of cellulose coloration for digital recognition and humidity response

Structural color is an eye-catching phenomenon in nature, which originates from the synergistic effect of cholesteric structure inside living organisms and light. However, biomimetic design and green construction of dynamically tunable structural color materials have been a great challenge in the field of photonic manufacturing. In this work, the new ability of L-lactic acid (LLA) to multi-dimensionally modulate the cholesteric structures constructed from cellulose nanocrystals (CNC) is revealed for the first time. By studying the molecular-scale hydrogen bonding mechanism, a novel strategy that electrostatic repulsion and hydrogen bonding forces jointly drive the uniform arrangement of cholesteric structures is proposed. Due to the flexible tunability and uniform alignment of the CNC cholesteric structure, different encoded messages were developed in the CNC/LLA (CL) pattern. Under different viewing conditions, the recognition information of different digits will continue to reversibly and rapidly switch until the cholesteric structure is destroyed. In addition, the LLA molecules facilitated the more sensitive response of the CL film to the humidity environment, making it exhibit reversible and tunable structural colors under different humidity. These excellent properties provide more possibilities for the application of CL materials in the fields of multi-dimensional display, anti-counterfeiting encryption, and environmental monitoring.