Bio‐Inspired Cholesteric Phase Cellulose Composite with Thermochromic and Circularly Polarized Structural Color for Multilevel Encryption

Abstract

The escalating need for enhanced cryptographic security necessitates the development of advanced materials designed for the secure storage and transmission of information. Drawing inspiration from the unique color‐altering and polarizing capabilities of beetles, this work develops a transparent, thermochromic, and circularly polarized cholesteric phase cellulose composite (CPCC). This is achieved by integrating self‐assembled hydroxypropyl cellulose with cholesteric liquid crystal (CLC) structure in tandem with a crosslinked poly(N‐isopropyl acrylamide) (PNIPAM) network. The crosslinking density impacts the response degree of thermochromism, which can be regulated by modifying the UV exposure time during PNIPAM production. The CLC structure in CPCC uniquely results in reflected right circularly polarized light. When coupled with waveplates, this mechanism inverts the rotation direction of the reflected light, creating orthogonal structural colors of different brightness levels under left and right circularly polarized light. The excellent transparency of CPCC facilitates seamless integration with the environment, offering optimal camouflage. Sophisticated techniques, such as color coding and Morse coding, can further be incorporated within the CPCC to increase encryption security and the complexity of decryption. Collectively, the CPCC's transparency, thermochromism, and chirality present significant potential in the design and development of materials for high‐security information encryption, contributing valuable insights to the field.

Beyond Color Boundaries: Pioneering Developments in Cholesteric Liquid Crystal Photonic Actuators

“…It has been shown that cellulose nanocrystals exhibit left-handedness, selectively reflecting left-handed CPL and transmitting right-handed CPL [ 94 ], and that the resulting color can be altered by the addition of glucose [ 95 ] or sodium chloride [ 96 ] or by applying an electric [ 97 ] or magnetic field [ 98 ] to a suspension of cellulose nanocrystals to induce a change in pitch value. Xiaoxiang Wen et al presented a methodological advancement in the fabrication of a thermochromic and circularly polarized cholesteric phase cellulose composite (CPCC) [ 99 ]. Drawing inspiration from the color-shifting and polarizing attributes observed in beetles, the CPCC is synthesized by combining hydroxypropyl cellulose with a cholesteric liquid crystal structure and a crosslinked PNIPAM network.…”

“…Since a CLCPA, which changes color due to stress–strain stimulation, could be subjected to various forms of deformation such as stretching, bending, and torsion, it could be used for the detection of body and joint movements [ 80 ] ( Figure 23 b). CLCPAs’ vibrant structural colors could be used for a wide range of temperature detection up to 50 °C [ 10 , 99 , 109 ] ( Figure 23 c). Visible shape/color changes could be observed during temperature changes.…”

“… Thermal response CLC photonic actuators. ( a ) The scanning electron microscope (SEM) image depicts the CLC structure of the cholesteric phase cellulose composite (CPCC) [ 99 ]. ( b ) Temperature-responsive structural color photographs showcase the CPCC’s diverse response degrees to temperature variations [ 99 ].…”

“…( a ) The scanning electron microscope (SEM) image depicts the CLC structure of the cholesteric phase cellulose composite (CPCC) [ 99 ]. ( b ) Temperature-responsive structural color photographs showcase the CPCC’s diverse response degrees to temperature variations [ 99 ]. ( c ) The arrangement and adaptive camouflage capabilities of a typical artificial chameleon robot [ 100 ].…”

Stimulus-responsive polymer materials toward multi-mode and multi-level information anti-counterfeiting: recent advances and future challenges

“…In particular, their adjustable optical properties have seen SRPs widely utilized in the field of information storage and anti-counterfeiting, and have aroused great interest. Specifically, when exposed to an external stimulus, such as light, 23,24 temperature, 25,26 ions, 27,28 electricity, 29,30 magnetic, 31,32 mechanical force, 33,34 humidity 35,36 (Fig. 1a), such intelligent systems undergo obvious photophysicochemical characteristics alteration.…”