Your best bet against skin cancer is sunscreen, which works by absorbing ultraviolet light and reflecting visible and near-infrared (NIR) light to protect your skin cells from the damaging rays of the sun. As one of the safest and most effective sun-blocking pigments, titanium dioxide (TiO2) is used in many brands of sunscreen—as well as in coatings designed to reflect sunlight off surfaces in a bid to lower cooling costs. Such coatings play an important role in keeping buildings cool in the face of climate change.
Although TiO2 pigments can reflect visible light well, they may not be as effective in reflecting NIR light. However, NIR reflectance is a key factor in a coating’s overall ability to reflect sunlight, or total solar reflectance (TSR), which is directly related to cooling performance.
One way to improve reflectance is by increasing the distance between TiO2 particles, which tend to clump in a coating film, particularly at high concentrations. To physically separate the particles, a team of researchers from A*STAR’s Institute of Chemical and Engineering Sciences (ICES) coated them with different shell materials and assessed their effectiveness.
“For cool coatings, we have to take cost into account so we used relatively cheap materials like poly(methyl methacrylate) and polystyrene to encapsulate TiO2,” explained study co-corresponding author Satyasankar Jana, a Senior Scientist at ICES.
When compared with bare TiO2, encapsulated TiO2 particles were more evenly spaced in the coating. Furthermore, just as light bends when it moves from air to water, the need for light to travel through materials with different refractive indexes improved the scattering of light, ultimately improving TSR by up to 7-10 percent and enhancing the cooling effect.
“In the lab, we observed a difference of 8°C under NIR irradiation. Under actual sunlight we observed a difference of close to 3°C for a small test panel,” said Alexander van Herk, a co-corresponding author on the study and a Principal Scientist at ICES. “This is considerable as we are comparing equal amounts of TiO2 and other components in the two samples, so this temperature difference is simply due to the encapsulation.”
Apart from coatings on urban surfaces, polymer-encapsulated TiO2 could also be used in high-end applications such as automotive coatings, Jana added. Building on their findings, the researchers are now studying if their pigment encapsulation approach can be used to improve NIR reflectivity in road markings and car coatings for better visibility in autonomous driving environments. “We are currently investigating this line of research with a project supported by an Industry Alignment Fund grant,” he said.
The A*STAR-affiliated researchers contributing to this study are from the Institute of Chemical and Engineering Sciences (ICES).