Bio‐Inspired Multifunctional Smart Windows: Surface Wrinkle‐Crack for Dynamic Optical and Wettability Modulations

Smart windows are promising to promote building energy efficiency. Bio-inspired smart windows are expected to fulfill the independent energy-saving and on-demand privacy modes simultaneously, while further improvement is necessary. Here, an improved composite based on tungsten-doped vanadium dioxides (W-VO2), silica (SiO2) nanospheres, and polydimethylsiloxane (PDMS) elastomers is reported. It is found that the composite can simultaneously fulfill the on-demand privacy and energy-saving modes under a low temperature of ≈45 °C. More importantly, the surface morphology effects are investigated on optical and wettability modulation and provide insight into the SiO2-based wrinkle formation mechanisms. It is demonstrated that surface wrinkles are more effective than cracks in achieving privacy mode, indicated by the diffraction patterns. Increasing the surface wrinkles and cracks also causes a change from hydrophilic to hydrophobic properties accompanied by the contact angle change from 19° to 115°, suggesting the potential for self-cleaning functionality. It is also demonstrated that SiO₂ spheres are essential in forming wrinkles: small gaps between nearby SiO₂ spheres promote localized strain and increase the overall Young's modulus, resulting in larger wrinkle amplitude. Combining the improved method and insight understanding, this work is expected to support future developments in mechano-/thermos-chromic materials, smart windows, and bioinspired optical materials designs.