Effect of Impregnation Route on the Thermal Behavior and Phase- Change Characteristics of PEG-600 Confined in Mesoporous Silica– Alumina

In this study, PEG-600/Silica- Alumina composites were developed as shape-stable phase change materials (PCMs) by using ultrasonic-assisted wet impregnation and vacuum impregnation methods to investigate the effects of the preparation method on their thermal performance and structural properties. The comparative evaluation highlights the role of synthesis route on pore-level PEG confinement and phase-change behavior. The mesoporous Si–Al support, with a surface area of 475 m² g⁻¹ and pore volume of 0.78 cm³ g⁻¹, provided an efficient porous framework for PEG loading. Nitrogen adsorption analyses showed significant decreases in surface area and pore size after impregnation, particularly for composites prepared by the vacuum impregnation method, indicating more effective pore utilization. Differential scanning calorimetry (DSC) revealed that the composite prepared with vacuum impregnation method (VPCM2) exhibited a melting temperature of 20.96°C and latent heat of 93.62 J g⁻¹, values close to those of pure PEG and indicative of preserved phase-change reversibility under thermal analysis conditions. FTIR and SEM analyses confirmed effective physical confinement, interfacial compatibility, and uniform PEG dispersion within the Si–Al framework, contributing to the enhanced structural integrity and leakage resistance. Overall, the results demonstrate that vacuum impregnation provides superior pore filling, improved phase-change efficiency and thermal response, and enhanced thermal reliability compared to ultrasonic-assisted wet impregnation for medium-temperature thermal energy storage applications. From a processing perspective, vacuum impregnation enables higher PEG utilization, which is beneficial for thermally efficient composite design.