Confinement effect of SiO2 framework on phase change of PEG in shape-stabilized PEG/SiO2 composites

PEG/SiO2 shape-stabilized phase change materials with various mass fractions and molecular weights of PEG were prepared by the sol–gel method. Polyethylene glycol (PEG) and tetraethyl orthosilicate (TEOS) were chosen as the phase change substance and the silica framework precursor, respectively. The as-prepared samples were characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM) techniques. It is shown that the silica framework strongly confined the crystallization of PEG. The crystallinity and thermodynamic performance of the composites were undesirable for PEG with molecular weight of 1500 even when the PEG content reached 80 wt%. The crystallinity and thermodynamic performances of the PEG/SiO2 composites first decline then improve with the increase of the PEG molecular weights, owing to the different confinement behaviors of the silica framework. Finally, we investigated the phase change mechanism of the PEG/SiO2 composites under the different confinement of the silica framework.