Fig. 12: Water/humidity responsive structural color actuators based on CNCs.

a Chemical structure of CNCs. b A sandwiched structure with PA-6 embedded between two CNCs/PEGDA layers showing reversible bending and twisting as well as reflective color change when exposed to a humid environment. Reproduced with permission⁷⁵. Copyright 2016, Royal Society of Chemistry. c A CNC/ PF resin composite bilayer with different helical pitch showing curling and color change when exposed to water. Reproduced with permission⁴⁸. Copyright 2014, Wiley-VCH. d PF resin/GO-containing CNCs films showing reversible unbending and color change when dipped in water and drying. e PF resin/GO-containing CNCs film with predetermined shapes treated with formaldehyde at selective regions and their responses toward a wetting–drying cycle. Reproduced with permission⁴⁷. Copyright 2019, Royal Society of Chemistry