Phase-Changing Polymer Film for Smart Windows with Highly Adaptive Solar Modulation

Area of Science:

• Materials Science
• Nanotechnology
• Energy Efficiency

Background:

• Efficient energy-saving applications require control over sunlight and thermal radiation through windows.
• Smart windows aim for high solar modulation (ΔTsol) and high luminous transmittance (Tlum).
• Conventional poly-N-iso-propylacrylamide (PNIPAm) hydrogels have limited applications due to volume contraction during phase transitions.

Purpose of the Study:

• To develop a novel composite hydrogel film for smart window applications.
• To enhance the performance of PNIPAm hydrogels by combining them with hydroxypropyl cellulose (HPC).
• To achieve high luminous transmittance and solar modulation in a durable smart window design.

Main Methods:

• Fabrication of composite hydrogel films using hydroxypropyl cellulose (HPC), W-doped VO2, and poly-N-iso-propylacrylamide (PNIPAm).
• Construction of a smart window prototype using a sandwich structure with the developed hydrogel film.
• Characterization of the smart window's optical properties (Tlum), solar modulation (ΔTsol), and thermal responsiveness (LCST).

Main Results:

• The smart window achieved a high luminous transmittance (Tlum) of 87.16% and a solar modulation (ΔTsol) of 65.71%.
• The composite hydrogel exhibited a lower critical solution temperature (LCST) of 29 °C and a volume shrinkage rate of 8.5%.
• The smart window maintained high solar modulation capability after 100 cycles of high- and low-temperature testing.

Conclusions:

• Combining HPC with PNIPAm effectively addresses the volume contraction issue in thermo-responsive hydrogels.
• The developed composite hydrogel smart window demonstrates excellent optical and energy-regulating properties.
• The material shows promising durability for practical applications in energy-efficient windows.