A bioinspired multilayer film with angle dependent and humidity responsive color-changing performances based on its crosslink networks

Color changing can immediately activate system of vision, which bring corresponding monitoring function without delay. Traditional color-changing sensor is not competent for the detection of large area, low-cost and easy preparing. Inspired by adaptive coloring strategies of beetle elytra, angle dependent and humidity responsive color-changing films are achieved with large area through convenient and low-cost technics of spin-coating and self-leveling. When observed at different angles, L 2B , L 2P and L 3G acquired with NPAM and HEMA-co-MMA layers can bring color-changing expect L 3P . And L 3G also conducts humidity responsive color-changing with stability from green to purple in variation from 46%rh to 84%rh and reversibly changing from purple to green while from high to low humidity, which ascribed to transformation between dehydration and hydration of NPAM layer with hydrophilic groups. To characterize the durability and stability in microscale, nano-indentation technology was used to reveal the nanomechanical properties of cross-link networks for NPAM and HEMA-co-MMA films. It was found out that the hydrophilic groups of networks can carry hydrogen bonds to enhance cross-link characteristic and low separation performance. This research provides insights into the simple and efficient technology for preparing functional material that displays potential applications in industrial, agricultural and military fields. Graphical Abstract