Stretchable Laminates with Tunable Structural Colors from Layered Stacks of Elastomeric, Ionic, and Natural Polymers.

Natural polymers such as plant-derived cellulose nanocrystals (CNCs) are renowned for color iridescence due to their internal helical organization, but they show modest stretchability and bending abilities, because of the brittle nature of highly crystalline needlelike nanocrystals. Herein, we report the highly stretchable composite materials built from these nanocrystals and branched ionic polymers (bIPs) with terminal amine-terminated poly(-isopropylacrylamide) (PNIPAM) stacked between elastomeric layers. These layered elastomeric composites preserve the high mechanical stretchability of polyurethane outer layers up to 150%. Furthermore, the toughness increased manyfold, due to the sequential initiation and arresting of concurrent transversal cracks within the reinforcing central nanocomposite layer. Moreover, vivid structural colors of CNC helical organization preserved within these laminated composites show the ability to respond to humidity and temperature. We suggest that these elastomeric composite laminates with preserved structural colors of helical nanocellulose organization can be considered to be promising candidates for demanding applications such as robust wearable sensors, flexible optical labels, and photonic devices.