Thermochromic Hydrogels with Dynamic Solar Modulation and Regulatable Critical Response Temperature for Energy-Saving Smart Windows

Conventional buildings consume about 40% of global energy, smart window technologies have been developed for sunlight modulation and energy management. Most current smart windows change from transparent to opaque as the temperature rises, which is detrimental to indoor lighting at daytime or privacy protection at night. In this work, a versatile thermochromic hydrogel system by introducing sodium dodecyl sulfate (SDS) micelles into a crosslinked copolymer of hydrophilic acrylamide and hydrophobic stearyl methacrylate (C-18) is developed. The liquid precursor solution can be encapsulated within two glass panels and in situ gelated to prepared smart windows, which showed excellent solar modulation ability (T-lum = 99.05%, DTsolar = 33.42%), dual responsiveness (thermal and pH) and tunable phase transition temperature (20-50 degrees C). Moreover, this design selectively blocks infrared light, while allowing ultraviolet and visible light through at daytime, which is beneficial for indoor illumination and heat insulation. When temperature drops at night, C-18 units aggregate within SDS micelles to increase their dimensions, causing enhanced light blocking properties (opaque) to protect the customers' privacy. The as-prepared hydrogel-based smart windows present a facile strategy to meet the stringent requirements of high transparency, excellent solar modulation ability, easy to fabricate and mechanical flexibility, holding great promise for the next-generation energy-saving buildings.