Synthesis and characterization of microencapsulated sodium sulfate decahydrate as phase change energy storage materials

Sodium sulfate decahydrate has been microencapsulated within a silica shell through a novel method of reverse micellization and emulsion polymerization. Tetraethoxysilane and 3-aminopropyl-triethoxysilane were used in conjunction as silicon precursors to form the silica shell, which encapsulated sodium sulfate decahydrate as a phase change material for thermal energy storage. The melting and solidifying temperatures of the microcapsules were measured as 33.6 degrees C and 6.0 degrees C, respectively, with associated latent heats of 125.6 kJ/kg and 74.0 kJ/kg. The phase segregation of various hydrate salts was inhibited by the confining effect of the silica mesopores. The size of the microcapsules could be regulated from 500 nm to 28 mu m simply by reducing the amount of surfactant (Triton X-100) deployed as a stabilizer. Confined by SiO2 matrix, heat storage properties of the hydrate salts were greatly improved. Sodium sulfate decahydrate microencapsulated within a silica shell is shown to be suitable for application in thermal energy storage.