New approach for sol–gel synthesis of microencapsulated n-octadecane phase change material with silica wall using sodium silicate precursor

• The n-octadecane microcapsules were synthesized using the sodium silicate precursor.
• The n-octadecane microcapsules presented a well-defined core–shell structure.
• The silica inner wall enhanced the crystallinity of n-octadecane.
• The thermal conductivity and durability were enhanced due to the silica wall.

A new silica encapsulation technique toward n-octadecane PCM (phase change material) was developed through sol–gel synthesis using sodium silicate as a silica precursor. Fourier transform infrared spectra confirm the chemical composition of the synthesized microcapsules, and wide-angle X-ray scattering patterns indicate good crystallinity for the n-octadecane inside silica microcapsules. Scanning electric micrographs demonstrate that the microencapsulated n-octadecane obtained at pH 2.95∼3.05 presents a perfect spherical morphology and a well-defined core–shell microstructure. Because the pH value of reaction solution determines the silica condensation rate and, thus, influences the balance between the self-assembly and polycondensation of silica precursors on the surface of n-octadecane droplets, the microcapsules could achieve a smooth and compact surface at pH 2.95∼3.05. The microencapsulated n-octadecane also exhibits good phase change performance and achieves a high encapsulation rate and high encapsulation efficiency in this synthetic condition. The encapsulation of n-octadecane with compact and thick silica wall can impart a high thermal conductivity and a good anti-osmosis property to the microcapsules, and can also improve the thermal stability of the microcapsules by preventing inside n-octadecane from thermally evaporating. Owing to the easy availability and low cost of sodium silicate, this synthetic technique indicates a high feasibility in industrial manufacture for the microencapsulated PCMs with inorganic walls.