Surface-Engineered Main-Chain Azobenzene-Containing Polyurethanes: toward Stimuli-Responsive Microstructure and Color Regulation

Abstract

Endowing material surfaces with on-demand, multistimulus responsiveness holds great promise for surface and interface engineering, but remains challenging. Herein, we report a versatile surface-engineering strategy to construct functional surfaces with tailorable microstructures and stimuli-responsive chromic properties using a main-chain azobenzene-containing thermoplastic polyurethane (Azo-TPU). The photoresponsive behavior and acid–base chromic mechanism of the synthesized Azo-TPU are systematically investigated. Specifically, by integrating a surface-wrinkling system, dynamic regulation of surface wrinkle microstructures is achieved via stimulus-induced stress relaxation and the generation of anisotropic stress fields. Meanwhile, acid–base-induced protonation/deprotonation of the azobenzene moieties enables reversible visual color switching between yellow and orange red. As a proof-of-concept application, a variety of sophisticated wrinkle patterns with tunable microstructures are facilely fabricated via a selective light-exposure strategy. Furthermore, various elegant patterns on the Azo-TPU modified functional fabrics can be acid-printed and base-erased within 30 s for multiple cycles, remaining legible for over 2 h under ambient conditions. Notably, the dual-stimulus responsiveness of the Azo-TPU enables independent of-demand control of surface microstructures and coloration, thereby offering great potential for applications in rewritable information storage, as well as the fabrication of microstructured arrays, photonic devices, and other multifunctional devices.