Subambient Passive Radiative Cooling with Reflective Paints (MgO-PMMA)

Abstract

This study investigates the development and performance of a passive radiative cooling paint formulated with magnesium oxide as the reflective pigment and PMMA combined with polyurethane as binders, using DMF and distilled water as solvents. The paint is designed to lower surface and indoor temperatures by improving solar reflectivity and thermal emissivity, offering a practical solution to reduce energy consumption in hot and humid climates. Material characterization using SEM and EDX confirmed that the MgO particles have a crystalline structure and wide size distribution, which enhance sunlight scattering, while PMMA provides good film formation and weather resistance, with both materials present at the micrometer scale. Preliminary tests comparing different pigment concentrations and solvents showed that using DMF with a 70% pigment volume concentration resulted in the lowest surface temperatures and the highest quality coating, producing a smooth and dense layer with strong adhesion to the surface. Field tests on miniature houses with various roof materials further demonstrated that the MgO-PMMA paint consistently achieved lower surface and interior temperatures than the surrounding air and a commercial white paint, with the curved zinc sheet roof delivering the best performance due to its reflective shape and improved airflow. Although the DMF based paint performed well, it also presented practical challenges such as a thick and slightly slimy texture, fast hardening time, and higher cost and handling concerns related to DMF’s properties. Overall, the results confirm that the MgO-PMMA paint has strong potential as a passive cooling solution for buildings, helping to reduce energy use and mitigate urban heat in warm climates. Further improvements in formulation, application methods, and the adoption of safer, more cost effective materials will be necessary to support wider practical implementation.