Preparation and characterization of PEG/SiO2 composites as shape-stabilized phase change materials for thermal energy storage

• The novel shape-stabilized phase change materials (ss-PCMs) are designed for building envelops.
• Stable core–shell structures of ss-PCMs are formed by impregnating PEG into mesoporous silica gel.
• The enthalpies of ss-PCMs vary from 63.4 J/g to 128.4 J/g.
• Thermal conductivity of ss-PCM with 2.7% graphite is 0.558 W m−1 K−1.
• ss-PCMs have high thermal stabilities and good compatibilities.

A novel sol–gel method was adopted to prepare polyethylene glycol/silicon dioxide shape-stabilized phase change materials (PEG/SiO2 ss-PCMs) with various PEG mass fractions. The gelatinization was carried out by adjusting temperature instead of adding coagulant. In PEG/SiO2 composites, PEG acted as the phase change material and silica gel served as the supporting material to keep the stable shape of the composites during the phase transition. Various characterization techniques were employed to investigate the structures and properties of the composites. Results showed that the composites exhibited the stable core–shell structures by impregnating PEG into multi-mesoporous silica gel; they could remain in the solid form even if the temperature exceeded the melting point of PEG. It was physical adsorption between PEG and silica gel, and the crystal structure of PEG component was unaffected, so that PEG in the composites retained an excellent phase change performance. The enthalpies of the composites varied from 63.4 J/g to 128.4 J/g (PEG mass fractions: 50–80%), which was proportional to PEG content. The thermal conductivities were increased to 0.558 W m−1 K−1 by addition of graphite in mass fraction of 2.7%. Moreover, the composites presented excellent thermal stabilities and possessed a broad applicable temperature range, and they were suitable for thermal energy storage applications in building envelopes.