Polyethylene glycol/fumed silica composites as shape-stabilized phase change materials with effective thermal energy storage

Shape-stabilized phase change materials (SSPCMs), adopting polyethylene glycol (PEG) as the phase change material (PCM) confined in fumed silica (FS) as the porous support, and their thermal energy storage properties were thoroughly characterized with varying PEG contents, 60-90 wt%. Given a highly interconnected porous structure and a high porosity (88%), FS offered plenty of cavities to confine a large amount of PEG with interactions such as surface tension, capillary, and interfacial hydrogen bonds (H-bond). The interfacial H-bonds negatively affected the crystallinity of PEG and decreased the thermal energy storage capacity, which could be relieved by a large content of confined PEG. The optimum 80 wt% PEG/FS SSPCM exhibited a high crystallinity of 93.1%, corresponding to a remarkable thermal energy storage capacity of 130.6 J g-1, and excellent thermal reliability after experiencing 500 melting/crystallization cycles. Moreover, it exhibited a reduced thermal conductivity compared to pure PEG, promoting heat transfer delay during melting and crystallization processes. The 80 wt% PEG/FS SSPCM combined with gypsum effectively retarded the thermal transfer compared to pristine gypsum, indicating the PEG/FS SSPCMs are suitable for potential applications in building thermal management.