Feather-inspired multi-stimulus-chromic multilayer composite films with selective modulation of solar spectrum and efficient thermal management for windows

Ordinary windows, as the least energy-efficient components in building energy consumption, cause significant heat loss/gain. Facing this challenge, smart windows are regarded as a key technology for reducing building energy consumption through their dynamic photothermal modulation capabilities. With the technological advancement, the trend toward multifunctionality and high performance in smart windows is inevitable, giving rise to multi-stimulus responsive light-modulating smart windows. Inspired by the unique multilayer structure and structural-pigmentary color synergy of non-iridescent bird feathers, this study proposes a multilayer film for smart windows. This film integrates a polydimethylsiloxane (PDMS)/SiO₂ mechano-solvatochromic layer with a PDMS/thermochromic microcapsule thermochromic layer. It can respond to strain, solvent and thermal stimuli through three unique mechanisms, regulating the structural/pigmentary color of each layer to achieve selective modulation of the solar spectrum. Based on the individual/coupled effects of different stimulus response, the film exhibits five modes. It not only achieves an outstanding 37.92% solar modulation efficiency and 48.25% luminous transmittance difference at 40% strain and 55°C, but also meets user preferences and emergencies. A Field test conducted in Shanghai in May shows that it can reduce the blackbody temperature in a model house by 16.3°C. A computational simulation for a building demonstrates that compared to ordinary window, the novel smart window can reduce the energy consumption of apartment heating, ventilation, and air conditioning by 51.62% and CO ₂ emissions by 46.31%, contributing to the achievement of carbon neutrality goals. This work provides a new solution for the high-performance and multifunctional development of smart windows.