Novel metal coated nanoencapsulated phase change materials with high thermal conductivity for thermal energy storage

Fast heat transfer is very important for practical application of phase change materials. Herein, a novel kind of silver coated nanoencapsulated phase change materials (NanoPCMs) with high thermal conductivity were prepared, and their properties were examined. Dopamine surface activation was carried out on silica nanocapsules containing n-octadecane, followed by electroless plating in Tollen's reagent. Chemical composition and crystallinity of the original silica nanocapsules, polydopamine modified NanoPCMs, and silver coated NanoPCMs were characterized by FT-IR, XPS, and XRD methods. Microstructure and morphology of these NanoPCMs were observed by SEM and TEM. Phase change property, thermal stability, thermal reliability, and thermal conductivity of these NanoPCMs were measured by DSC, TG, thermal cycling test, and laser flash methods, respectively. Although the mass-based latent heats decline obviously after silver plating due to high density of metallic Ag, the volume-based latent heats only exhibit minor decrease. These NanoPCMs crystallize mainly based on heterogeneous nucleation and show low supercooling, by introducing n-octacosane as nucleating agent. Moreover, they can keep constant phase change properties during multiple melting/solidifying thermal cycles. Most importantly, the apparent thermal conductivity of the silver coated NanoPCMs increases significantly from 0.246 to 1.346 W/m K. Owing to these excellent properties, the silver coated NanoPCMs are promising for thermal energy storage and thermo-regulation applications.