Thermotropic phase-change hydrogels with precise temperature adjustability as smart curtains for building energy-saving

Many studies have shown that buildings account for 30–40 % of total energy consumption worldwide. Due to the high thermal diffusion coefficient of ordinary windows, energy consumption of traditional buildings is relatively high. Therefore, it is very important and necessary to develop building energy-saving technologies to solve these problems. In this work, an anionic surfactant (sodium dodecyl sulfate) with adjustable critical solution temperature is introduced into polyvinyl alcohol (PVA)-based hydrogels to render the hydrogels phase-transition ability. By adding binary solvents of water and glycerol (GL), the prepared hydrogels show outstanding anti-freezing and anti-drying properties as well as high transparency. In addition, the hydrogels have excellent mechanical and flame-retardant properties. As smart curtains, the hydrogel reported in this work can protect privacy at night, allowing the sunlight to pass through during the day (without consuming additional energy) and effectively reducing indoor temperatures (up to 4.9 °C). This hydrogel not only reduces indoor temperature and saves energy, but also has the potential for large-scale industrialization because of the simple preparation process and the use of cost-effective raw materials. This allows the hydrogel to be used in applications such as building facades, energy saving, and privacy protection.