A multi-stimulus responsive nanogel actuator with the π-π stacking interaction self-assembly and application for bioinspired smart skin with light, heat and humidity responses and superb UV resistance

The fabrication and development of assemblies of bionic smart skin with multi-stimulus response and multi-color tunable properties is a major challenge in the field of advanced materials and smart wearable devices. In this work, an amphiphilic functional nanogel switch connected by long polyether chain segments containing bis-spiropyran with the π-π stacking interactions was designed. A multi-stimulus responsive color-changing nanogel actuator (SP-PEG-NA) was constructed using ionic liquid-assisted self-assembly. A composite bionic smart skin (WPU/SP-PEG@CF) was prepared by compositing SP-PEG-NA, waterborne polyurethane (WPU) and flexible cotton fabric based on physical cross-linking. The smart skin possesses multiple color-changing properties in response to light, heat and humidity. Even under ultra-low UV intensity (0.025 mW/cm 2 ), WPU/SP-PEG@CF also exhibits significant photochromic properties. Surprising, the smart composite constructed with the nanogels possessed extremely high UV shielding performance (UPF 628.68) and photocontrolled hydrophobic-hydrophilic transition properties. The self-assembled nanogel actuators greatly improved the stimulus–response sensitivity. The multiple supramolecular noncovalent interactions of the nanogel actuator such as hydrophilic long polyether structures hydrogen-bonding and π-π stacking interactions endowed nanogel highly self-assembly properties. They showed excellent multi-stimulus response in color-changing, versatility and reversibility. The multi-stimulus responsive and multifunctional smart composites prepared using self-assembled nanogel has potential applications in smart wearable materials, sensors and information display.