As a wise and profound teacher, nature provides numerous creatures with rich colors to us. To biomimic structural colors in nature as well as color changes responsive to environmental stimuli, there is a long way to go for the development of free-standing photonic films from natural polymers. Herein, a highly flexible, controllably iridescent, and multistimuli-responsive cellulose nanocrystal (CNC) film is prepared by simply introducing a small molecule as both plasticizer and hygroscopic agent. The presence of the additive does not block the self-assembly of CNC in aqueous solution but results in the enhancement of its mechanical toughness, making it possible to obtain free-standing iridescent CNC films with tunable structural colors. In response to environmental humidity and mechanical compression, such films can change structural colors smoothly by modulating their chiral nematic structures. Notably, the chromism is reversible by alternately changing relative humidity between 16 and 98%, mimicking the longhorn beetle Tmesisternus isabellae. This chromic effect enables various applications of the biofilms in colorimetric sensors, anticounterfeiting technology, and decorative coatings.

No abstract

Biomimetic optical cellulose nanocrystal (CNC) materials have shown great potential for application in colorimetric sensing, anticounterfeiting, and decorative coatings because of simple recognition by the naked eye; however, how to simultaneously solve the inherent brittleness of CNCs as well as achieve multisensing functions is still a big challenge. Here, we propose a new coassembly strategy of CNCs and citric acid (CA) to fabricate freestanding photonic CNC films. The chiral nematic structure and visible structural colors can be adjusted in a wide color range by varying the CA content. Owing to the plasticizing effect, the resulting CNC-CA films display high flexibility and can be folded freely. Notably, such films can sense different external signals, including compression, ethanol and alkali, by changing apparent structural colors. Additionally, for volatile chemicals, the color changes are reversible, ensuring repeating applications. Given the high mechanical performance and multisensing performance, this method represents a simple but effective way to construct highly flexible and multifunctional photonic CNC materials.

Undergraduates commonly suffer from stress and anxiety; therefore, it is imperative to find restorative places on campus. Although blue and green spaces are good for recovery and stress relief, previous studies have failed to determine other types of restorative spaces on campuses. Using a bottom-up participatory smartphone photo survey, this study recruited a sample of 243 students from Sichuan Technology and Business University in China, and the results were as follows: (1) potential restorative spaces on campus were grouped into five categories: green, blue, gray, living, and study space; (2) no significant differences were found in the assessment of the five restorative spaces, all of which showed positive effects; (3) the five restorative spaces were linked with four restorative characteristics in different ways, with green, blue, gray, and living space showing the “being away” characteristic (refuges from the hassles of everyday life, indicate geographical or psychological distance), and gray and study spaces showing the “fascination” characteristic (effortless attention); (4) visit duration played an important role in the environment’s potential to promote recovery. A shorter visit duration owing to a lack of infrastructure and interest points may contribute to reduced benefits. This study has important implications for the design and management of restorative environments on college campuses.