Synthesis and characterization of microencapsulated paraffin with TiO₂ shell as thermal energy storage materials

In this study, the microencapsulated phase change material with paraffin as core and inorganic TiO₂ shell was successfully synthesized by in situ hydrolysis and polycondensation of tetrabutyl titanate in a nonaqueous oil-in-water emulsion using formamide as aqueous phase. The chemical compositions, crystalline structure, morphology and microstructure of paraffin@TiO₂ microcapsules were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The thermal properties and thermal stability of the microcapsules were measured by differential scanning calorimeter (DSC) and thermo-gravimetric analyzer (TGA). FT-IR and XRD results proved that there was no chemical reaction between paraffin core and TiO₂ shell material. SEM images indicated that the paraffin@TiO₂ microcapsules showed a regular spherical shape with the average diameters of 2–5 µm with a smooth shell. SEM and TEM studies also confirmed the paraffin was fully encapsulated with TiO₂. DSC analysis indicated that the microcapsules had similar phase change behaviors as those of pure paraffin. Typical sample froze at 52.24 °C with a latent heat of 110.42 J g⁻¹ and melt at 60.41 °C with a latent heat of 107.54 J g⁻¹, of which the encapsulation ratio achieved to 54.58%. TGA results indicated the thermal stability of paraffin was improved by the protection of TiO₂ shell through the encapsulation.