Tough asymmetric thermochromic ionogels via dynamic in situ phase separation for passive/active smart optical switching

Despite significant advances in thermochromic materials (TCMs) for smart optical switching, achieving simultaneous optimization of optical switching, mechanical robustness, and environmental tolerance remains a critical challenge for their real-world implementation. Herein, inspired by the Janus architecture of beetle carapaces, we present tough asymmetric thermochromic ionogels (ATIs) fabricated via dynamic in situ phase separation. The ATIs integrate a thermoresponsive light-scattering layer (LCST: 28°C to 41°C) and a mechanically reinforced supporting layer through sequential free-radical polymerization. The resulting material exhibits high transparency (>85% at 20°C), ultralow-temperature resistance (transparent at −70°C, even at −196°C), and exceptional toughness (tensile strength >5 MPa, toughness >17 MJ m-3). Leveraging hydrophobic ionic liquid as solvent, the ATIs achieve reversible optical switching (transmittance <10% at 40°C) without encapsulation, with autonomous adhesion (>400 N m-1 peel strength on glass). Applied to smart cooling windows, ATIs reduce solar radiation by 56.8% while enabling aesthetic customization. Combined with indirect/direct Joule heating technology, ATIs enable active optical switching and even dynamic projection display, offering a scalable platform for all-weather adaptive optical systems.