Articulating the phase-separated microstructure of stearyl acrylate-based thermochromic polymers for application in smart windows

Smart windows that are based on thermoresponsive materials are becoming a strong competitive candidate in smart window research since they can dynamically respond to the environmental temperature, granting us comfort and privacy without increasing building energy expenditure. The focus of this study is a thermochromic phase-changing polymer material that can switch between an opaque crystalline phase and a transparent amorphous phase. The two major constituents of the polymer film are stearyl acrylate and ethoxylated trimethylolpropane triacrylate, both acrylate compounds. At room temperature, the polymer film possesses a semi-crystalline structure that scatters visible light and infrared efficiently. Above the transition temperature, the film undergoes order-to-disorder structural transition thus becomes light-transmitting. The fabricated film in this study presented 71.4% transmission modulation over the whole solar spectrum, 70.9% for the visible light modulation, and 68.5% for the infrared modulation. The thermoresponsive polymer layer in this study is equipped with a polyurethane acrylate-based, transparent heater embedded with silver nanowires that heats the polymer film through joule heating until it reaches the transition temperature. The fabricated composite transparent heater is also capable of achieving fast heating speed while maintaining high visible transparency and long-term thermal stability. A smart window device was assembled by sandwiching the thermochromic layer (150 μm) between the transparent heater layer (90 μm) and pure polyurethane acrylate protection layer (90 μm). By switching on and off the DC power source, the device can switch freely between opaque and transparent states according to personal needs