Morphology-controlled synthesis of microencapsulated phase change materials with TiO2 shell for thermal energy harvesting and temperature regulation

Abstract

In this work, we designed and fabricated three types of n-eicosane/TiO2-based microcapsules with different morphologies through an emulsion-templated interfacial polycondensation route, followed by the structure-inducing formation of TiO2 shell. As we expected, the resultant microcapsules achieved the tubular, octahedral and spherical morphologies as well as a well-defined core-shell microstructure under the structure-directing control with different crystallization promoters. X-ray diffraction confirmed that the tubular microcapsules obtained a crystalline TiO2 (B) shell, whereas a brookite TiO2 shell was formed for the octahedral and spherical microcapsules. According to the thermal analysis under the isothermal and nonisothermal conditions, the tubular microcapsules showed the fastest thermal response due to their specific internal nanostructures, and the spherical microcapsules presented the largest amounts of charged and discharged heat because of their highest effective encapsulation ratio of n-eicosane core. These three types of microcapsules achieved a good energy storage capability in an order of the spherical microcapsules > the octahedral microcapsules > the tubular microcapsules, and all of them presented a diverse range of superior performance including excellent temperature-regulating and photocatalytic capabilities, good thermal reliability and durability, good shape stability and prominent heat charging/discharging performance when used for thermal energy harvesting and temperature regulation.