Authors: J. Mandal,† Y. Chen,† C. Tsai, S. Shrestha, N. Yu, Y. Yang.
Journal Link: Science Advances, 6 (17), eaaz5413 (2020).
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Summary: This work shows that paints can be carefully engineered to absorb visible colors complementary to the one desired (e.g. yellow, if you desire blue), and at the same time, transmit invisible solar heat. When a thin layer of such a paint is painted above a highly reflective coating (say a white paint, or some of the designs below), it can reflect solar heat much better than traditional single layer designs. This enables bi-layers (color paints on white coatings) to stay much cooler (e.g. by 5ºC) than traditional coatings of the same color, while using less colorants.
Note: Bilayer designs have previously been explored by Ronnen Levinson et. al. at the Heat Island Group in Lawrence Berkeley National Laboratory. This work adds to those by providing physical justifications for the bilayer design, and proposing that a near-infrared (NIR) transparent top layer may be generally better than one that scatters NIR.