Keeping the indoor cooler without power consumption
Hydrogel Smart Window
consists of a scalable hydrogel-inorganic material for passive thermal control. A water-retentive thermochromic hydrogel and low-emissivity polymer film regulate solar radiation without power for cooling indoor temperature which saves up to 34% of energy.
Key Features & Advantages
Novel maintenance-free polymer composite helps cool the indoor temperature by a maximum of 9°C
Transparent coating blocking 90% solar thermal energy, while keeping >70% light to the room
Zero energy consumption and can save 20-40% energy for cooling
Mass production ready: Large-area roll-to-roll coating
This invention presents a scalable hydrogel-ITO smart window designed for passive solar and thermal regulation in buildings, addressing the urgent need for energy-efficient glazing in hot climates.
The smart window integrates a water-retentive thermochromic hydrogel (PCA-Na/PNIPAM) with a low-emissivity ITO-PET film, enabling simultaneous modulation of visible, near-infrared (NIR), and long-wave infrared (LWIR) radiation. The hydrogel dynamically switches between transparent and opaque states near room temperature (15.5-25.7°C), regulating solar heat gain without external power. Meanwhile, the ITO layer provides ultra-low thermal radiation which in turn enhances thermal insulation.
Compared with conventional smart windows, this chemical and structural design offers three key advantages:
Enhanced durability, achieved by PCA-Na-induced water retention that prolongs hydrogel service life;
Efficient thermal management, combining high solar modulation (>60%) with low LWIR emissivity (~0.32);
Practical scalability, enabled by simple lamination and low-cost materials suitable for large-area fabrication.
Outdoor field tests demonstrated a maximum indoor temperature reduction of nearly 9°C under direct sunlight compared with a glass-based window, through which the air temperature inside rapidly increased to 45°C. Building energy simulations further predict annual cooling energy savings of up to 34% in representative hot regions, including Abu Dhabi, Hong Kong, and Phoenix. This invention provides a power-free, cost-effective, and scalable solution for next-generation smart windows, offering strong potential for applications in sustainable and energy-efficient envelopes for commercial buildings, greenhouses, and vehicles.
Left: Temperature lower than the critical temperature; Right: Temperature higher than the critical temperature
