• "cool" paints
• nanoparticles
• reflectance
• synthesis
• thermal management
• thermoplastic hollow microspheres

Recently, a growing interest has been shown in the use of near infrared (NIR) reflective pigments for the development of cool coatings for different surfaces. This proved necessary because, when the sunlight hits an object part of the radiation is absorbed, consequently leading to a heating of its surface. This phenomenon is due to the near infrared (NIR) component of the electromagnetic spectrum of light (700-2500 nm): the NIR radiation, in fact, has the necessary energy to activate the vibration of chemical bonds, consequently triggering a rise in the temperature on the surface. The heat is then conveyed into the material by conduction, raising the temperature of the internal side by convection. In this work, we investigated the NIR reflective properties of coatings containing Expancel® 461 WE20d36, thermoplastic hollow microspheres (THM) that, thanks to the great difference in refractive index between the wall and the void, diffuse Vis-NIR radiation very well, helping the scattering of these wavelenghts on the external surface of the microsphere. Furthermore we tried to enhance the reflective power of the film integrating indium oxide nanoparticles (In2O3) into this resin-microspheres system, aiming at testing their ability to block NIR radiation when incorporated in polymeric matrices. In2O3 NPs were synthesized by thermal decomposition of organometallic precursors and characterized by transmission electron microscopy (TEM) and powder x-ray diffraction (XRD) techniques to determine their morphological and structural characteristics. The optical properties of the colloidal dispersions and of the derived coatings based on polymeric nanocomposites have been studied by UV-VIS-NIR spectroscopy to assess their ability to reflect NIR radiation. The reflective properties were evaluated by total solar reflectance analysis (TSR) while the "Cooling Effect" provided by the prepared coatings was determined using an ORIELs LCS-100 solar simulator as a source. In the end, preliminary studies on the plasmonic absorption of indium tin oxide (ITO) NPs in the IR range were conducted, in order to harness the absorbed heat for a possible water heating in solar thermal systems, creating in this way new devices to generate thermal energy from the solar one.