Fig. 9: Cellulose-based representative photonic structures and the corresponding stimulus responsiveness.

a Schematics (top rows) and images (bottom rows) of representative photonic architectures^{163,170,171,172}. Images reproduced with permissions: 1D-helicoidal structure¹⁶³, Wiley-VCH; 2D-grating structure¹⁷⁰, Springer Nature: Nature Photonics; Hierarchical chiral nematic structure: left¹⁷¹, Elsevier; right¹⁷², Wiley-VCH. b Structure and structural color changes of CNCs under chemical and humidity stimulations^155,175. Adapted with permission from ref. ¹⁵⁵. Copyright 2020 American Chemical Society. Reproduced from ref. ¹⁷⁵, with permission from Wiley-VCH. c Schematics and photographs showing the color changes of the CNC-elastomer composite under stretching¹⁸³. Reproduced from ref. ¹⁸³, with permission from Springer Nature: Nature Communications. d Temperature-responsive behavior and polarized optical microscopy images of patchy PNIPAM-grafted CNCs and “brush” PNIPAM-modified CNCs¹⁹². Reproduced from ref. ¹⁹², with permission from Wiley-VCH