A novel smart window based on co-crosslinked hydrogel with temperature self-adaptability and anti-freezing functions for building energy saving

Thermochromic smart windows based on hydrogels with adaptive regulation of solar radiation have attracted an increasing attention due to their potential in temperature management. However, hydrogels with extremely high water content may freeze, leading to the risk of transparency reduction and even window breakage in cold environment. In this study, co-crosslinked P(NIPAM-co-AM)@GLY@PVA hydrogel with excellent solar radiation regulation and anti-freezing performance was prepared by introducing antifreeze glycerol (GLY) and polymer polyvinyl alcohol (PVA). By adjusting the amount of GLY, PVA and hydrophilic AM, P(NIPAM-co-AM)@GLY@PVA hydrogel showed a satisfactory thermochromic performance, with a luminous transmittance (T_lum) of 68.05 %, a solar modulation ability (ΔT_sol) of 62.11 %, a lower critical solution temperature (LCST) of ∼24 °C and an antifreeze temperature of −15 °C. The thermal management experiments proved that the thermochromic@anti-freezing (TCA) smart window assembled based on P(NIPAM-co-AM)@GLY@PVA hydrogel had an excellent performance in managing indoor temperature and cyclic stability. This work may open a new avenue to solve problems in the application field of hydrogel-based smart windows.