KCA/Na₂SiO₃/PNIPAm hydrogel with highly robust and strong solar modulation capability for thermochromic smart window

Thermochromic smart windows have strong competitive advantages in the realm of building energy conservation. However, achieving thermochromic smart window with a lower critical solution temperature (LCST), high solar modulation (Delta T-sol), and excellent visible light transmittance (T-lum) remains a great challenge. Here, a novel composite hydrogel based on polydiisopropylacrylamide (PNIPAm) doped with carrageenan (KCA) and Na2SiO3 was developed for high-performance smart window. The lower LCST of PNIPAm was precisely tuned in a range from 25 degree celsius to 28 degree celsius by controlling the content of added Na2SiO3. The inclusion of KCA diminishes agglomeration within the gel system and enhances both T-lum and Delta T-sol. As a result, the KCA/Na2SiO3/PNIPAm exhibits a high T-lum (87.37 %), Delta T-sol (69.65 %), a lower LCST (27.2 degree celsius), and a high atmospheric window emissivity (0.962). The smart window achieves temperature drop of 12.3 degree celsius under direct sunlight, and keeps highly stable even after 100 cycle tests high and low-temperature durability due to its robust solar modulation capability. This work offers valuable insights for developing high-performance and robust thermochromic smart windows and holds promising applications in building energy conservation.