This research investigates the effects of incorporating expanded graphite (EG) at 5 wt % into organic phase-change materials (PCMs) on the thermophysical properties, as well as the shape stability of the resulting composites. Decanoic acid (melting point, 33.2 °C), 1-dodecanol (melting point, 23.7 °C), and their eutectic mixture were selected as the PCMs for this investigation. Pure PCMs, along with their eutectics, were encapsulated with titanium dioxide (TiO2) shells. The decanoic acid was coated with TiO2 at 50 wt % via in situ polycondensation, and the eutectic PCMs were encapsulated with TiO2 at 67:33 wt % core–shell composition via the sol–gel method; while expanded graphite was synthesized separately by chemical oxidation and incorporated into the composites. The Brunauer–Emmett–Teller surface area analysis revealed a significant enhancement from 3.26 m2/g in the TiO2-coated eutectic PCM to 64.21 m2/g in the EG-infused decanoic acid composite, attributed to the porous EG network that promotes superior heat flow. Latent heat measurements using differential scanning calorimetry demonstrated that TiO2-encapsulated PCMs achieved the highest storage capacity of 85.49 J/g, highlighting excellent energy retention. The contact angle measurements revealed a transition from hydrophobic behavior (98.05° for TiO2-coated decanoic acid) to superhydrophilic nature (14.75° for TiO2-coated eutectic PCM with EG), indicating enhanced surface affinity that strengthens capillary retention within EG pores and minimizes leakage. This was further validated by leakage tests confirming over 94.9–97.1% material retention, which was 96.4–96.8% for EG composites. Thermogravimetric analysis demonstrated 40–78% enhanced thermal stability, with EG-containing samples maintaining integrity up to 693–697 °C and higher residual mass.
Naseem et al. (Mon,) studied this question.