Temperature-responsive hydrogel with ultra-large solar modulation and high luminous transmission for “smart window” applications

Abstract

The application of a thin film of poly(N-isopropylacrylmide) hydrogel to thermochromic smart windows has been investigated. As the thickness of the hydrogel increased from 26 to 200 μm and the testing temperature increased from 20 to 60 °C, the solar modulating ability (ΔT_sol) increased and the luminous transmittance (T_lum) decreased. Compared with the best reported results for the most studied inorganic VO₂ thermochromic coatings, an unprecedented good combination of near-doubled average T_lum (70.7% vs. 42.8%), higher ΔT_sol (25.5% vs. 22.3%) and lower transition temperature (∼32 °C vs. ∼68 °C) could be achieved by hydrogels with an optimized thickness. Good durability and reversibility were established with the correct sealing of the sandwich structure.