Phase change characteristics of shape-stabilized PEG/SiO2 composites using calcium chloride-assisted and temperature-assisted sol gel methods

This study is focused on the preparation of a novel shape-stabilized phase change materials (SSPCM) employed in thermal energy storage. Two sol gel assisted methods including calcium chloride (CaCl2)-assisted one and temperature-assisted one were adopted to prepare polyethylene glycol/silicon dioxide (PEG/SiO2) composites, and the influence on phase change characteristics between two assisted methods were studied. The prepared composite remained solid state without leakage above the melting point of PEG when the weight percentage of PEG (PEG content) was 80%. Differential scanning calorimetry (DSC) results indicated that the phase change enthalpy of the composite prepared by temperature-assisted method was higher than that of CaCl2-assisted one. X-ray powder diffraction (XRD) results showed SiO2 and CaCl2 were detrimental to the perfect PEG crystallization, especially CaCl2 which transformed the crystal structures and significantly affected the phase change of PEG. Fourier transform infrared spectroscopy (FTIR) indicated the interaction of PEG and SiO2 was physical action. However, PEG and CaCl2 was chemical action, the coordinate bonds were formed and the free movements of PEG were restricted. It was concluded that the temperature-assisted one was a promising method to prepare SSPCM due to its advantages of good thermal property and simplicity in preparation. In addition, polarizing optical microscopy (POM) suggested PEG was dispersed into mesoporous silica structure and formed stable core-shell structures. There was no leakage of melted PEG after many heating and cooling cycles. Thermogravimetry (TG) results showed that SSPCM prepared by temperature-assisted method had good thermal stability and could be applied in a broad temperature range.