Design and synthesis of magnetic microcapsules based on n-eicosane core and Fe3O4/SiO2 hybrid shell for dual-functional phase change materials

Magnetic microcapsules based on an n-eicosane core and Fe3O4/SiO2 hybrid shell were designed as a new type of dual-functional phase change materials. A series of magnetic microcapsule samples were synthesized through a two-step route. Fe3O4 nanoparticles were first self-assembled on the interface of n-eicosane droplets in a Pickering emulsion system, and then the silica matrix was fabricated through interfacial polycondensation of tetraethyl orthosilicate in the sol-gel process. On the basis of scanning and transmission electron microscopic investigations, the resultant magnetic microcapsules were found to present a perfect spherical morphology with a uniform particle size of 4-6 mu m, and they also showed a well-defined core-shell structure constructed by a smooth and compact shell. The chemical structures of the magnetic microcapsules were confirmed by Fourier transform infrared spectroscopy, and meanwhile, their chemical compositions from surface to inner layer were determined by X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, and Raman scattering spectroscopy. These magnetic microcapsules achieved a good thermal-storage capability and high thermal reliability according to their phase-change performance detected by differential scanning calorimetry (DSC). The encapsulation efficiency and energy-storage efficiency were also deduced from the DSC data of the magnetic microcapsules synthesized with different mass ratios of core to shell. Most of all, the magnetic microcapsules exhibited a superparamagnetic nature with extremely low magnetic retentivity and coercivity. With such a dual-functional feature, the magnetic microcapsules developed by this study could provide a new applicable route for some high-tech fields to fulfill both thermal energy storage and magnetic effectiveness. (C) 2014 Elsevier Ltd. All rights reserved.