Low-cost and fast-thermal-response Mo–PVA/PNIPAM hydrogel-based smart windows for monitoring indoor temperature under hot environments

Abstract

In recent years, global warming has posed a series of challenges to comfortable human living. While some techniques can offer mitigation, their energy-intensive nature renders them unsuitable for widespread adoption in underdeveloped regions. To address these shortcomings, a cost-effective smart window with indoor-temperature regulation was developed. It was fabricated by integrating {Mo₁₅₄} with a blend of the polyvinyl alcohol/poly(N-isopropyl acrylamide) (PVA/PNIPAM) hydrogel. Based on the temperature-induced phase transformation ability of PNIPAM, the composite hydrogel could be used to regulate the indoor temperature. Concurrently, PVA can mitigate the problem of volume shrinkage from PNIPAM phase transition. More importantly, {Mo₁₅₄} can reduce the lower critical solution temperature (LCST) of the Mo–PVA/PNIPAM hydrogel as well as provide photothermal properties for intelligently sensing the outside temperature. The smart window could display a favorable sunlight modulation property (ΔT_sol = 80.8%) and a rapid heating rate response upon light exposure. Due to the presence of {Mo₁₅₄}, the smart window became opaque to block sunlight when the indoor temperature exceeded 28.9 °C. This feature could maintain indoor cooling in the hot summer without any energy consumption. Moreover, the Mo–PVA/PNIPAM-based smart window demonstrated favorable durability, maintaining its functionality after 100 heating (40 °C)-cooling (20 °C) cycles, indicating its reliability for long-time usage and suitability for the underdeveloped areas with limited electric energy.