Advances in thermoresponsive hydrogel-based smart windows for building energy saving

Smart windows offer a means to dynamically regulate sunlight and significantly reduce energy consumption in buildings. In recent years, thermochromic hydrogels have attracted considerable attention due to their high solar modulation capability and their operation without energy input. This paper presents the development of poly(N-isopropylacrylamide) (PNIPAm)-based thermochromic hydrogel materials, along with other emerging thermochromic hydrogel materials, including cellulose ethers, pillar[n]arenes, and poly(N-vinylcaprolactam) (PNVCL). The discussion encompasses the optical properties, energy-saving capabilities, and cold and thermal cycling characteristics of each thermochromic hydrogel material. Furthermore, the paper outlines general development strategies for thermochromic hydrogel smart windows, addressing aspects such as color regulation, photo-thermochromic mechanisms, electrothermal technology, enhanced freeze resistance, and energy savings and privacy protection. Finally, the paper discusses the future opportunities and challenges associated with thermochromic hydrogel smart windows. • Thermochromic hydrogel smart windows enable building energy savings via PNIPAm and cellulose ether materials, optimized by photothermal/electrothermal strategies. • A comprehensive review of thermochromic hydrogels from traditional to emerging materials for smart windows, highlighting multifunctional integration. • A systematic review on the design, optimization, and application of thermochromic hydrogel smart windows.