Ultra-strong anti-freezing hydrogel-based smart window with wide geographical adaptability

Smart windows, capable of dynamically regulating indoor heat, offer a promising avenue for effectively reducing energy consumption. Hydrogel-based smart windows are excellent at thermal modulation and daylighting, but they are difficult to commercialize globally due to problems like winter ice formation, which can affect thermal insulation, daylighting, and structural integrity, as well as an impractical cloud point temperature (t_cp). To solve these issues, a ternary anti-freezing system consisting of ethylene glycol (EG), glycerol, and water is proposed. With the t_cp regulated at 31.6°C, the system strikes a balance between outstanding daylighting (91.89%) and solar modulation ability (78.32%). Furthermore, the system shows resilience even below −30.0°C and long-term stability, which qualifies it for use in densely populated regions even with severely cold weather. To further illustrate the distinct impacts of EG and glycerol, the optical characteristics and t_cp of binary systems containing EG and water as well as glycerol and water were examined. The durability test includes severely cold temperature of −30.0°C and solar exposure temperature of 60.0°C. This work would offer insights to advance the field’s understanding of anti-freezing capability modification in smart windows and advance the development of environmentally and energy-efficiently designed buildings.