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A method for generating a solar reflective blue-grey paint coating with yellow-green luminescence that is cost-effective, industrially scalable, widely applicable, easily repairable, super-non-wetting, self-cleaning, and solar reflective, is introduced. The coating can be manufactured using as-received commercially available materials and following a simple industrial procedure. Grinding the coating surfaces using emery papers with appropriate grit numbers can readily yield appropriate surface roughness, generate suitable micro-grooves and expose micro- and nano-particles on the coating surfaces, thus endowing the coating surfaces with super-non-wettability and self-cleaning property. The surface free energy of the coating only depends on the dispersive component and both the Lewis acid component and the Lewis base component are 0 mN/m. The solar reflective blue-grey coating with solar reflectance of 0.808 can yield a cooling effect of 22.6 °C relative to a flat or low-sloped concrete roof on a typical clear summer sunny day. It emits yellow-green luminescence during the night, thus decorating the buildings to some extent when applied to the external walls of buildings. Although the super-non-wettability of the coating surfaces might be destroyed mainly by the periodic spraying of water (simulated by 400 h of artificial accelerated weathering tests), the super-non-wettability and the self-cleaning property can be completely re-established after roughening the weathered coating surfaces using emery papers with appropriate grit numbers. In terms of optical properties, the solar reflective blue-grey coating with yellow-green luminescence has good resistance to artificial accelerated weathering.

The conventional way to fabricate current sub-ambient daytime radiative cooling (SDRC) systems is to maximally suppress the cooler's solar absorption and substantially improve its selective emissivity only in the atmospheric transparency window. This greatly limits the selection of materials and their practical applications. In this paper, an alternative method, which combines sunlight-triggered fluorescent cooling, particle scattering, and broadband infrared radiation, was presented for creating serial eco-friendly coatings with the SDRC effect with conventional cost-effective building materials. The presence of conventional fluorescent pigments in the coating composition increased the effective direct-normal solar reflectance via sunlight-excited fluorescent emissions to the level required for SDRC. When applied to various substrates, the serial coatings exhibited distinct SDRC effects under direct and strong sunlight in typical temperate monsoon climate regions such as Beijing. The observed sub-ambient temperature reduction of the coating with yellow–green fluorescence over an aluminium plate was 3.5 °C under a peak solar intensity of 996 W/m2, yielding a cooling power of 45.7 W/m2 under a peak solar intensity of 981 W/m2. Compared with the conventional cool white coatings, the large-scale application of the coating to urban surfaces is predicted to reduce a city's air temperature by approximately 1 °C and thereby decrease the Heat Island Intensity. Additionally, the method proposed in this paper was generic and expanded the SDRC design paradigm, thereby promoting SDRC as a viable energy-efficient technology.

The method to create cool gray coatings colored with mixtures of black and white pigments was described in a companion paper. In the current article, the method to prepare colorful cool gray coatings by mixing pairs of pigments of complementary colors and titanium dioxide rutile is introduced. The qualified cool light blue–gray and orange–gray coatings are created by mixing complementary cobalt aluminate blue and cromophtal yellow paste with the white coatings in appropriate proportions. The cool light to moderate yellow–gray and violet–gray coatings are formulated by blending complementary nickel titanate yellow and dioxazine purple paste and the white coatings in suitable proportions. The eligible cool light green–gray and red–gray coatings are colored with mixtures of complementary cobalt titanate green and irgazin red paste and the white coatings in appropriate proportions.

The particle size distributions of three commercially available titanium dioxide pigments were measured, and their effects on the optical properties of the pigments were investigated. The Altiris 550 and 800 pigments possess larger median particle size and wider size distributions than those of the conventional titanium dioxide rutile. The visible (VIS) reflectance, the solar reflectance and the lightness of the films and coatings singly pigmented with any of these three pigments decrease as the pigment particle size increases. The VIS transmittance and near-infrared (NIR) reflectance both increase as the pigment particle size increases. The main reflection band of the coatings shifts farther into the NIR region with increasing pigment particle size. The partially VIS-transmitting Altiris pigments enable the NIR and the solar reflectance of cool non-white coatings to be improved, thereby yielding metameric matches to the desired colors.

We describe the method for creating nominally cool gray coatings by mixing titanium dioxide rutile and black pigments that include chromite iron nickel black, manganese ferrite black spinel, perylene black and dioxazine purple. Although the solar reflectance of the gray coatings prepared by adding chromite iron nickel black and manganese ferrite black spinel pastes separately into a white coating are higher than that of the standard gray coating of colors of similarly lightness with the mixtures of carbon black and titanium dioxide rutile, they are actually not qualified cool gray coatings. The light gray coatings colored with a mixture of perylene black and titanium dioxide rutile are eligible cool gray coatings with a green shade. The gray coatings produced by mixing titanium dioxide rutile and dioxazine purple and chrome titanium yellow are also real cool coatings with a violet shade.

The factors affecting the optical properties of a cool, brown coating were systematically investigated using a UV/Vis/NIR spectrophotometer to optimize its solar reflectance. Zinc iron chromite brown is a partially near infrared (NIR) transmitting colorant. Over bare substrates, the NIR and solar reflectances of the coatings generally but not always increase when the reflectance of the substrates increases; the roughness of the substrate surface lowers both values. When applied over reflective white basecoats, the NIR and solar reflectances of the coatings increase as the basecoats thicken and saturate above a threshold value. The NIR reflectance and solar reflectance of the cool brown coating system also decrease as the topcoat thickness and the pigment concentration increase. The computed absorptance of the films containing only an acrylic emulsion and zinc iron chromite brown increases as the pigment concentration and film thickness increase.

The effects of manufacturing processes and artificial accelerated weathering on the solar reflectance and cooling effect of cool roof coatings were investigated using UV/vis/NIR spectrophotometry, laser diffraction spectrometry, optical microscopy and scanning electron microscopy. The solar reflectance and the cooling effect of the coatings were found to correlate positively with the grinding speed (over a constant grinding time) and grinding time (at a constant grinding speed) due to an improved dispersion effect of TiO2 particles. Artificial accelerated weathering slightly reduces the solar reflectance of cool roof coatings, and its influences on the cooling effect of cool roof coatings are negligible within the experimental error.

The physicochemical properties of two newly developed dirt-resistant cool white coatings were systematically measured in light of the relevant standard testing methods, and the influences of dirt accumulation and washing on the long-term cooling performance of cool coatings were investigated and discussed. Both cool white coatings owe their outstanding physicochemical properties to the optimized formulations, high glass transition temperature and minimum film formation temperature of selected aqueous self-curing acrylic emulsions. The high solid content was also influential. Dirt accumulation leads to a decline in the cooling performance of coatings, which may be almost fully restored by simply washing the coatings with a mild soap solution.