The thermochromic smart window and thermo-electrochromic device(T-ECD) based on PNIPAm/Ppy composite hydrogel for fast phase transition

Thermochromic smart windows possess great application potential in terms of building energy conservation. Herein, a novel smart window is designed by combining thermochromic poly(N-isopropylacrylamide) (PNIPAm) and polypyrrole (Ppy). The photothermal conversion effect of Ppy could effectively accelerate the phase transition of PNIPAm. The Ppy could provide extra heat for PNIPAm hydrogel, the phase transition time of PNIPAm/Ppy would be reduced to 3 min(12 min for pure PNIPAm hydrogel). The smart window exhibits excellent solar modulation efficiency(53.7 %). Different concentrations of KCl could regulate phase transition temperature of PNIPAm between 20 and 32 °C. Under irradiation of simulated light for 20 min, the water temperature of test tube covered by PNIPAm/Ppy smart window is 3.5 °C lower than that of blank glass. Moreover, T-ECD based on PNIPAm/Ppy could reduce phase transition time to 90 s. The electrochromic property of Ppy could endow T-ECD with more colours, and The T-ECD exhibits high solar modulation efficiency(63.0 %) which could decline transmittance to 0.2 %. PNIPAm/Ppy composite hydrogel provides new ideas for the design of thermochromic smart windows and thermo-electrochromic dual-response devices.