Boosting the NIR reflective properties of perylene organic coatings with thermoplastic hollow microspheres: Optical and structural properties by a multi-technique approach

This study reports for the first time the use of thermoplastic hollow microspheres (THM) in combination with a perylene bisimide pigment (Paliogen® Black L0086 (P-black)) for the preparation of acrylic coatings with near-infrared (NIR) reflecting and cooling characteristics. VIS-NIR spectra showed that P-black solid dispersions provide reflectance values in agreement with the P-black content and its crystalline nature. The introduction of THM with average diameter of 25 ± 5 μm with the same weight content of P-black did not substantially affect the crystalline nature of the pigment within the organic coating even if a decreasing of the long range order in the molecular packing of the perylene chromophores emerged from XRD and solid-state NMR investigations. Noteworthy, the addition of the THM successfully contributed in the exponential raising of the solar reflectance (SR) of coated black substrates, i.e. reaching up to the 22% at the highest organic layer thickness of 255 μm. The effective combination between THM and P-black was well reflected on the temperature of the back side of the coated surface after irradiation with a solar simulator, i.e. with a maximum cooling effect of about 6 °C.