Electroless plating of copper layer on surfaces of urea–formaldehyde microcapsule particles containing paraffin for low infrared emissivity

Abstract A copper coating was deposited by electroless plating on the surfaces of urea–formaldehyde microcapsules containing paraffin (UFP) particles. This composite microcapsule structure had low infrared (IR) emissivity and maintained a constant temperature, and could be used in IR stealth applications. The electroless copper layer formation and its micro-appearance, and the effect of the copper layer on the IR emissivity and thermal properties of the composite microcapsules were investigated. The IR emissivity of the composite microcapsules at wavelengths of 1–14 μm gradually decreased with increasing copper mass on the surface. After formation of an integrated copper layer, the rate of IR emissivity decrease was lower. This is because the copper coating improves the surface conductivity of the UFP; a high conductivity results in high reflectivity, which leads to a decrease in IR emissivity. The lowest IR emissivity achieved was 0.68. The phase-change enthalpy of the composite microcapsules decreased with increasing amount of copper coated on the surface because of the high density of copper. When the mass increase of the UFP after electroless copper plating was about 300%, the composite microcapsules had low IR emissivity (about 0.8) and a high phase-change enthalpy (80 J/g).