Influence mechanism of ammoniated modified binary composite cement on thermal properties of PEG and optimization of thermal properties

Preparing self-encapsulated cement-based energy storage materials (CCPCM) by combining water-soluble phase change materials with cement is an effective approach to functionalizing cement-based materials for energy storage. However, because of the pore structure and surface polarity characteristics of cement stone pores, the loss of thermal properties of PCM is serious. In this study, a silane coupling agent (APTES) was used to ammoniate the cement base, resulting in a significant enhancement of the thermal properties of the prepared polyethylene glycol (PEG)/ordinary silicate-sulfoaluminate cement (OPC-CSA) phase change composite. The influence of chemical modification on the thermal properties of the phase change composite (APTES-CCPCM) was investigated from the perspective of phase change kinetics. The results show that the latent heat of APTES-CCPCM increased by 67 % compared to the control sample (A0). Differential scanning calorimetry (DSC) tests revealed that APTES-CCPCM exhibited a shorter half-crystallization time, lower activation energy, and faster crystallization rate during the non-isothermal crystallization process. Specifically, the half-crystallization time ($t_{1/2}$) was reduced by 72 %, the apparent activation energy ($△E_a$) decreased by 28 %, and the crystallization rate ($\upsilon$) increased by 76 %. Additionally, when the PEG content reached 70 wt%, APTES-CCPCM showed no leakage, demonstrating that the addition of APTES achieved a dual optimization of thermal performance and impermeability. Moreover, APTES-CCPCM demonstrated excellent chemical compatibility, and the cement matrix's original mesoporous structure and PEG's ordered crystallization were not greatly affected.