Direct Ink Writing of 4D Structural Colors

摘要

Additive manufacturing with stimuli-responsive materials—4D printing—isa rapidly growing field, with direct ink writing allowing deposition of awide variety of materials. The synthesis of a humidity-sensitive cholestericliquid crystal oligomer ink is reported. With the responsive cholesteric ink,demonstrator devices exhibiting the ink’s “four dimensionality” are printedin disparate fashions: as a structural color change or as a preprogrammeddeformation mode. After printing, the photonic ink changes color in responseto atmospheric humidity, demonstrated as a hydrochromic coating preciselydeposited atop a 3D-printed beetle. After activation in aqueous acid, thebeetle exhibits vibrant color shifts across the visible spectrum. Alternatively, ascallop-inspired actuator with a 3D-programmed structural color is selectivelytreated with acid, to allow reversible “opening” and “closing” when exposedto humid and dry air, respectively. The ink enables additive manufacturingof both monolithic and multimaterial stimuli-responsive, shape-changing,structurally colored objects, toward broad application of cholesterics in future“smart,” 4D structurally colored devices.