Scalable Thermochromic Polymer Blends Based on Leuco Dye-Doped Polycaprolactone for Solar Reflectance Modulation

Thermochromic systems based on leuco dye/developer/cosolvent ternary mixtures exhibit reversible color changes. However, to apply these mixtures as self-supporting materials, microencapsulation is generally required, which complicates fabrication and limits scalability. In this study, scalable thermochromic polymer materials suitable for large-area applications, including smart roofs, were fabricated via a simple physical blending process using semicrystalline polycaprolactone (PCL) as a cosolvent. In this system, 2′-anilino-6′-(dibutylamino)-3′-methylfluoran and dodecyl gallate were employed as the leuco dye and the developer, respectively. Upon the phase transition of PCL, the ternary mixtures demonstrated reversible color-change behavior with a transmittance change from 5.0% to 66.2%. The optical properties of the thermochromic polymer blends containing leuco dye-doped PCL were dominated by the refractive index difference between the continuous and dispersed phases. Polystyrene and blends of poly(lactic acid)/poly(methyl methacrylate) were investigated as continuous phases for refractive index-mismatched and -matched polymer blends, respectively. The refractive index-mismatched blend transitioned from light absorption to light scattering upon heating, resulting in temperature-adaptive reflectance regulation suitable for smart roof applications. The refractive index-matched blend showed high transmittance at elevated temperatures and achieved temperature-responsive reflectance by laminating an Ag mirror onto the blend. Their potential for smart roof applications was evaluated by comparing the temperature dependence of reflectance spectra with the solar irradiance spectrum, and the results indicated that the refractive index-matched blend with an Ag mirror layer enables more efficient solar reflectance regulation by up to 20%.