TiO2-P25 Enhanced Thermochromic Coatings for Energy Efficient Roofing: Evaluating Long-Term Performance through Accelerated Aging Tests

Author(s)

Hidalgo-Araujo, Ana Carolina ; Salomao, Rafael ; Berardi, Umberto ; Dornelles, Kelen Almeida

• Document type: Journal article
• Source: BUILDING AND ENVIRONMENT; v. 281, p. 13-pg., 2025-08-01.

Abstract

As global warming intensifies, passive cooling strategies are critical in reducing energy consumption, mitigating the urban heat island effect, and reducing greenhouse gas emissions. This study investigates the energy performance and durability of thermochromic coatings applied to ceramic and fiber cement roof tiles in two climatically different Brazilian cities: Manaus (humid equatorial) and Curitiba (subtropical). The coatings of microencapsulated organic pigments combined with rutile TiO2 were enhanced with colloidal silica (SiO2) and anatase TiO2-P25 nanoparticles to improve long-term stability. Accelerated aging tests were performed according to ASTM D7897, and solar reflectance was measured according to ASTM E903 and G173. This data was incorporated into EnergyPlus simulations under projected climate conditions for 2050. Simulation results showed that lowering the pigment's transition temperature (TT) to 20 degrees C significantly improved energy performance in subtropical climates. In Curitiba, thermochromic roof coatings reduced energy consumption by up to 7.3% in unaged and 5.2% in aged samples compared to the ceramic roof reference. However, savings could reach 11.3% with improved optical contrast between the two-color states of the pigment. Adding a TiO2-P25 protective layer effectively reduced pigment degradation, as evidenced by solar reflectance losses that were approximately 50.4% lower below the TT and 33.3% lower above the TT, compared to unprotected samples. These results highlight the potential of thermochromic coatings to improve the energy efficiency of buildings in climates with significant temperature variations and underscore the need for tailored formulations. The study also calls for region-specific accelerated aging protocols, natural weathering testing, and further research to enhance color contrast and reduce photodegradation to improve the durability and reliability of thermochromic pigments. (AU)

• FAPESP's process: 24/00850-9 - Characterization and thermo-energetic simulation of multifunctional tiles
• Grantee: Ana Carolina Hidalgo Araujo
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• FAPESP's process: 22/03655-7 - Reducing energy losses in industrial processes with high-efficiency thermal insulation of microporous castable calcium silicate produced from elements of biomass: eggshells and rice husk ash
• Grantee: Rafael Salomão
• Support Opportunities: Program for Research on Bioenergy (BIOEN) - Regular Program Grants
• FAPESP's process: 24/10060-5 - COATINGS FOR THE BUILDING ENVELOPE AND THE AGING ASSESSMENT OF ABSORPTANCE TO SOLAR RADIATION: proposition of a national method for accelerated aging practice
• Grantee: Kelen Almeida Dornelles
• Support Opportunities: Regular Research Grants
• FAPESP's process: 22/14074-5 - Thermochromic and self-cleaning tiles: an adaptive and resilient roof
• Grantee: Ana Carolina Hidalgo Araujo
• Support Opportunities: Scholarships in Brazil - Doctorate