Energy-efficient smart window based on a thermochromic microgel with ultrahigh visible transparency and infrared transmittance modulation

Both high visible transparency and strong solar modulating ability are highly required for energy-saving smart windows, but conventional responsive materials usually have low transparency and a narrow solar transmittance range. Herein, we report a significant advance toward the design and fabrication of responsive smart windows by trapping a novel V0.8W0.2O2@SiO2-doped poly(N-isopropyl acrylamide) (PNIPAm) thermochromic microgel within two glass panels. The smart window is highly transparent to allow solar transmittance at low temperatures, while it turns opaque automatically to cut off the solar energy gain when exposed to sunlight. With a remarkably low content (1.0 wt parts per thousand) of dopant, the V0.8W0.2O2@SiO2/PNIPAm (VSP) microgels exhibited an ultrahigh luminous transmittance T-lum of 92.48% and solar modulation Delta T-sol of 77.20%. This superior performance was mainly attributed to the V0.8W0.2O2@SiO2 doping inducing a reduction in the PNIPAm particle size and a change in the internal structure. Also, W-doping decreased the phase-transition temperature (T-c) of VO2 from 68 degrees C to similar to 30 degrees C (close to the T-c of PNIPAm), contributing to infrared transmittance modulation. In particular, the smart window showed excellent energy saving during daytime outdoor demonstrations, where the practically achievable cooling temperature reached up to 15.1 degrees C. This new type of thermochromic microgel offering unique advantages of shape-independence and scalability together with soundproof functionality has potential applications in energy-saving buildings and greenhouses.

Automated summary

The innovative V0.8W0.2O2@SiO2/PNIPAm (VSP) microgels embedded in the smart window exhibit high transparency and solar modulation abilities. The doping of V0.8W0.2O2@SiO2 helps reduce particle size and improve internal structure, while W-doping decreases the phase-transition temperature of VO2 for infrared transmittance modulation. The smart window shows significant energy-saving capabilities and potential applications in buildings and greenhouses.