Self-Assembly Synthesis of Microencapsulated n -Eicosane Phase-Change Materials with Crystalline-Phase-Controllable Calcium Carbonate Shell

Novel microencapsulated phase-change materials based on an n -eicosane core and calcium carbonate (CaCO 3 ) wall have been synthesized through a self-assembly method. The resultant microcapsules presented rhombohedral and spherical morphologies when the synthesis was performed at different concentrations of surfactant. These two types of the n -eicosane microcapsules also exhibited a well-defined core–shell structure. X-ray diffraction patterns and Fourier transform infrared spectra confirmed that the rhombohedral microcapsules achieved a calcite CaCO 3 shell, whereas the shell of spherical microcapsules were composed of the vaterite CaCO 3 . The crystalline phase of the CaCO 3 shell could be controlled by the concentration of surfactant, sodium dodecylbenzenesulfonate, and a crystalline transition from calcite to vaterite occurred when the synthesis was carried out at the surfactant concentration of 3.0 mmol/L. The investigation of phase-change behaviors demonstrated that the encapsulation of n -eicosane enhanced its crystallinity in the α-form and thus led to an increase in crystallization temperature. The spherical microcapsules also exhibited higher encapsulation efficiency and energy-storage efficiency than the rhombohedral ones. The thermal conductivity of the n -eicosane microcapsules was significantly enhanced due to the fabrication of a highly thermally conductive CaCO 3 shell, and accordingly, the supercooling of n -eicosane was suppressed. Considering the easy availability and low cost of CaCO 3, this synthetic technology is worthy extending to the encapsulation of other PCMs with a CaCO 3 shell, and it also exhibits a good prospect in the industrial manufacture of microencapsulated PCMs with inorganic shells.