Novel metal coated nanocapsules of ethyl esters fatty acid eutectic mixture as phase change material with enhanced thermal conductivity for energy storage applications

In the present study, metal coated nanocapsules of ethyl stearate-ethyl palmitate eutectic phase change material (PCM) with high thermal conductivity were synthesized by in-situ emulsion polymerization followed by trisodium citrate reduction method. HRTEM analysis reveals the formation of core-shell structure with uniform spherical morphology and EDX results showed the presence of metal coating over silica shell. Phase change property of the eutectic mixture and nanocapsules were measured using DSC. Metal coated nanocapsules exhibited better thermal stability, conductivity and reliability determined by TGA, laser flash and thermal cycling analysis. Nanocapsules can persist constant phase change properties even after 1000 melting/freezing thermal cycles. Most significantly, the thermal conductivity of metal coated nanocapsules increases from 0.257 +/- 0.007 (eutectic mixture) to 0.660 +/- 0.019, 0.693 +/- 0.020 and 0.713 +/- 0.021 Wm(-1) K-1 for cobalt, copper and silver coated nanocapsules respectively. Similar to silver coated nanocapsules, copper and cobalt coated nanocapsules can also prove to be a promising material for thermal energy storage applications.