Design and fabrication of dual-functional microcapsules containing phase change material core and zirconium oxide shell with fluorescent characteristics

Abstract The traditional microencapsulated phase change materials (PCMs) only have a single function of thermal energy storage. In this study, we designed and synthesized a new type of PCMs-based microcapsules containing an n -eicosane core and ZrO 2 shell with the dual-functional characteristics of latent-heat storage/release and photoluminescence. The chemical structures and compositions of the resultant microcapsules were characterized by Fourier -transform infrared spectroscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray spectroscopy. These microcapsules exhibited a spherical morphology with a uniform size distribution and well-defined core–shell structure according to the observation of scanning and transmission electronic microscopy. The powder X-ray diffraction patterns confirmed that only the amorphous ZrO 2 shell was formed in the sol–gel process. However, the F − ions could induce the phase transition from the amorphous ZrO 2 shell to the crystalline one consisting of monoclinic and tetragonal phases. The photoluminescence characterization indicated that the microcapsules with the crystalline ZrO 2 shell could generate the purple-colored and green-colored luminescence after excited by UV radiation at a wavelength of 296 nm, whereas only the green-colored luminescence was recorded after excitation toward the microcapsules with the amorphous shell. Most of all, the dual-functional microcapsules revealed good phase-change properties, and meanwhile, they achieved a high thermal-storage capability, high thermal reliability, and good thermal stability as a result of encapsulation of the compact ZrO 2 shell. The dual-functional microcapsules developed by this work show potential applications for intelligent fibers or textiles, electronic devices, thermosensitive and photosensitive sensors, information-storage units, etc .