*A Review on Phase Change Materials for Sustainability Applications by Leveraging Machine… DOI: http://dx.doi.org/10.5772/intechopen.114380*

efficient distribution and extraction of heat during the phase change process, further curtailing supercooling and enhancing the effectiveness of the PCM for thermal energy storage. Gelling agents also contribute to the creation of a more homogeneous PCM mixture within the material. This homogeneity significantly reduces the occurrence of regions within the PCM where supercooling can manifest, fostering uniform phase change behavior [67, 79, 80].

Gelling agents significantly alter the molecular arrangement of phase change materials (PCMs), facilitating phase changes at desired temperatures. Acting as nucleation sites, they initiate solid crystal formation, promoting crystallization and increasing PCM viscosity. This increased viscosity restricts molecular movement, accelerating the transition from a supercooled to a solid state, thereby reducing supercooling. Gelling agents also lower the energy barrier for nucleation, ensuring quicker solidification. Some agents enhance PCM thermal conductivity, improving heat distribution and extraction, further minimizing supercooling, and boosting thermal energy storage effectiveness. Additionally, they contribute to a more homogeneous PCM mixture, preventing uneven supercooling and ensuring uniform phase change behavior [69, 79].

Gelling agents enhance energy storage efficiency by diminishing supercooling, thereby reducing energy losses, and ensuring predictable phase change behavior through consistent nucleation. They improve thermal management by keeping the PCM within its intended temperature range and extend its lifespan by preventing phase separation across thermal cycles. Additionally, gelling agents boost heat transfer and thermal conductivity for quicker charging and discharging, minimize leakage risks by solidifying the PCM, and ensure compatibility with system components, reducing corrosion. Their use simplifies handling due to the semisolid state and offers versatility for various thermal energy storage needs.

#### *3.3.2 Recent developments in gelling agents*

Recent advancements in gelling agents have aimed to enhance performance, sustainability, and versatility across industries. The focus has shifted toward natural and renewable agents like agar-agar, carrageenan, and pectin, alongside bio-based alternatives to lessen environmental impacts of PCM-based systems. Microencapsulation techniques enable precise control over thermal energy release, improving efficiency and stability in PCM systems. Stable PCM emulsions created with gelling agents offer better stability and heat transfer. Hybrid gelling agents combine traditional and nanomaterials for superior thermal properties, while customization for specific PCM materials optimizes phase change temperature and viscosity. Sustainability is emphasized through biomass-derived or waste-material gelling agents, aligning with broader environmental goals [55].
