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Summary In this experimental study, thermal aging test for investigating the variations in thermal and chemical properties of two selected organic phase change materials (PCMs) has been carried out. Polyethylene glycols (PEGs) of molecular weight of 2000 and 10 000 have been considered as potential latent heat thermal energy storage (LHTES) materials for investigation. The aim of this study is to identify the probable variations in thermal properties and chemical structures of PEGs after melting/freezing cycles repeated for 1500 times. The differential scanning calorimetry (DSC) technique was adopted for measuring the thermal properties such as melting point and latent heat of PCMs. In order to study the variations in PCM's chemical functional groups, Fourier transform infrared (FT‐IR) spectroscopy was used. Thermal durability property after the cycling test was investigated using thermogravimetric analysis. The DSC measurements indicated that PEG2000 experienced a maximum variation of about 4°C in melting point while the latent heat of fusion reduces by 16% after the cycle test. PEG10000 shows a variation of about 0.3°C in melting point and 15% of the latent heat of melting after the entire cycle test. The spectral investigation confirms that there are no variations in the functional groups of selected materials after cycle test, which can be inferred as chemical stability of them. The thermal gravimetric analysis curves show that both PEGs are thermally quite durable as well after such large number of melt/freeze cycles. Thermal cycling results and economic analysis confirm that both PEGs are potential PCMs for passive solar thermal management purposes. Highlights Synthesis of polyethylene glycol‐based binary eutectic mixtures. Accelerated thermal cycle test of eutectic mixtures. Binary mixtures were found chemically stable. Charging/discharging rates of PEG are controlled. Novelty Statement This paper presents the thermal performance of two polyethylene glycols, viz., PEG2000 and PEG10000. These materials were melted and solidified 1500 times for testing their suitability as thermal energy storage materials, and it was found that these materials are stable enough to store solar energy for five years. They found to be suitable for many solar energy storage applications.

The present study focused on the preparation of form-stable composites of 1-tetradecanoic acid (TDA)/titanium dioxide (TiO 2) powder via a facile impregnation method. The use of powdered TiO 2 as porous material and thermal conductivity enhancer for TDA is a novel attempt. The morphological, chemical, and crystalline properties of form-stable composite PCMs (Fs-CPCMs), containing different amounts of TiO 2 , were characterized using field emission scanning electron microscope, Fourier transform infrared spectroscopy, and X-ray diffraction techniques. The finding supports that the produced composites were chemically and structurally stable. The latent heat storage (LHS) properties of composites were obtained from differential scanning calorimeter instrument, and the findings revealed that the Fs-CPCM with 50 mass% TDA has a melting temperature of 52.04 C and a considerably good LHS capacity of 97.75 J/g. The thermal conductivity of TDA was increased remarkably by the addition of TiO 2 micro particles. The results obtained from thermogravimetric analysis and thermal cycling test exhibited that the Fs-CPCM, containing 50 mass% TiO 2 , possesses great thermal degradation durability, cycling chemical stability, and thermal reliability. This composite PCM can be very well used for passive thermal management of electronic devices, automotive components, photovoltaic thermal hybrid designs, solar air/water heating systems, etc.

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