Unravelling the role of TiO2 nanoparticles on the optical performance of dark colourants for coatings

The growing concern on energy savings in buildings, particularly related with cooling needs, has led to the search of new constructive solutions. Frequently, darker colour coatings are used in buildings for aesthetics purposes. However, such coatings have low reflectance, absorbing a large portion of the solar radiation. The associated heat gains enhance the building cooling demand and may reduce the service life of renderings owing to the increased thermal stresses in comparison to light colour coatings. The aim of this study was to assess the influence of size (30-5000 nm), optical band gap energy and concentration (0-20%) of TiO2 nanoparticles in a conventional black colourant for building applications. We confirm that the use of TiO2 nanoparticles increases the reflectance of the colourant and demonstrate that 50 nm is the most adequate nanoparticle size for reflectance enhancement. Furthermore, the colourimetric parameters are also affected by TiO2 incorporation, with the colour difference becoming increasingly noticeable to the human eye with increasing TiO2 concentration. Such results can lead to new formulations of solar reflective coatings are able to reduce the overall cooling load, particularly in warm climates with high cooling demands.