Precise control over tunable translucency and hysteresis of thermo-responsive hydrogel for customized smart windows

In view of global warming and following fossil energy consumption caused by the using of heavy-loaded air conditioners, smart windows, which can intelligently regulate solar radiation, became a highly anticipated strategy to slow down the pressure. As most of the traditional hydrogel-based smart windows abruptly switch between transparent and opaque making a sudden change in temperature and light, we established a poly-N-isopropylacrylamide (PNIPAM) thermo-responsive hydrogel system with additional cross-linking of chitosan and Al3+, which exhibited a smooth thermo-response during heating and a novel recovery hysteresis during cooling. By enabling additional gentle transition in translucency, we are able to retain a comfortable indoor temperature/lightness balance during an increase in outdoor temperature, in avoidance of sudden indoor darkness at elevated temperature. By enabling additional control in the thermo-response hysteresis, this methodology provides a solution to continuously shield the dazzling afternoon sunshine until a comfortable outdoor temperature is reached. And the response degree and response temperature can be adjusted by the contents of chitosan and Al3+, respectively, so that the material can be customized personally. Moreover, we discovered that the hydrogel-based smart window system constructed by this methodology bears notably enhanced strength, toughness and conductivity, making it a comprehensively promising candidate for customizable smart windows.