Design and characterization of a SiO2-TiO2 coating containing organic and inorganic thermochromic pigments and optimized with TiO2-P25 for improved long-term performance in energy-efficient roofing

This experimental study focuses on developing and characterizing thermochromic roof coatings contributing to energy-efficient building solutions. It addresses two key challenges: the limited durability of organic thermochromic pigments and the lack of research on applying thermochromic materials to opaque surfaces, especially inorganic pigments. Two coatings were developed: whereas the first contained a microencapsulated organic pigment (TC), the second used inorganic vanadium dioxide-based particles (VO 2 -W). Both were applied to ceramic and fiber cement tiles with a formulation that combined a binder (colloidal silica, SiO 2 ) and titanium dioxide (TiO 2 ) to improve durability. The novelty of the paper was the addition of a TiO 2 -P25 protective layer that retarded photodegradation and improved the long-term stability of the TC pigment. Coating components were evaluated using differential scanning calorimetry, solar reflectance, scanning electron microscopy, infrared spectroscopy, and X-ray diffraction. Coating performance was assessed regarding solar reflectance, thermal emissivity, and hydrophobicity. The results showed that the TC coating responded dynamically to temperature changes, indicating potential for improving buildings' thermal comfort and energy efficiency. On the other hand, the VO 2 -W coating showed limited performance in the infrared. In particular, TC coatings with TiO 2 -P25 exhibited 57 % less degradation below the transition temperature and 37 % less when heated. The main finding of this study demonstrated that TiO 2 -P25 significantly improved the durability of organic thermochromic coatings, offering a promising strategy to reduce the need for artificial cooling, reduce CO 2 emissions, and mitigate the urban heat-island effect. The results also addressed critical gaps in the durability of organic thermochromic pigments and the application of inorganic pigments to opaque surfaces. • Thermochromic coatings are applied to ceramic and fiber cement roof substrates. • A TiO 2 -P25/SiO 2 layer enhance pigment stability and overall coating durability. • TiO 2 -P25 layers reduce the solar reflectance loss of the organic thermochromic coating. • The results address critical gaps in the durability of organic thermochromic pigments.