Development and characterization of retro-reflective colored tiles for advanced building skins

Three types of microspheres were tested: i) clear barium titanate glass microspheres; ii) hemispherically aluminum coated barium titanate glass microspheres; iii) hemispherically aluminum coated barium titanate glass microspheres with an additional fluoropolymer coating. The obtained tiles were investigated with a spectrophotometric analysis, a study of the spatial distribution of the reflected radiation, a colorimetric analysis to evaluate changes in tiles' original color. Reflectance is increased by clear barium titanate glass microspheres, while is almost halved by aluminum-coated spheres. All the three types of microspheres provide strong RR behavior for incident light directions from 0° to 60° with respect to the surface normal. Nevertheless, the aluminum-coated microspheres change completely the tiles' original color, making the application of the aluminum RR tiles very limited. Clear barium microspheres instead improve the optic properties of the original tiles, with negligible effects on the color.