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 (CaCO3) 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 CaCO3 shell, whereas the shell of spherical microcapsules were composed of the vaterite CaCO3. The crystalline phase of the CaCO3 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 alpha-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 CaCO3 shell, and accordingly, the supercooling of n-eicosane was suppressed. Considering the easy availability and low cost of CaCO3, this synthetic technology is worthy extending to the encapsulation of other PCMs with a CaCO3 shell, and it also exhibits a good prospect in the industrial manufacture of microencapsulated PCMs with inorganic shells.