Encapsulation methods for phase change materials – A critical review

Currently, non-renewable resources are heavily consumed, leading to increased global warming resulting from the production of carbon dioxide etc., phase change materials (PCMs) are regarded as a solution to mitigate these global crises attributed to their promising thermal energy storage capability. In this critical review, the thermal properties of different encapsulation methods of PCMs are summarised and compared. Encapsulation ensures that PCMs are used safely and efficiently, therefore the method needs to be thoroughly investigated and improved before their practical implementation. The applicable thermal properties for different encapsulation techniques and encapsulation materials such as particle diameter, enthalpy, encapsulation efficiency and thermal cycling times are reviewed. Future researchers are advised to measure and report thermal conductivities, displaying them in a convenient manner; many studies ignore this parameter, hindering research progression. Evaluation criteria for mechanical properties should be developed to enable comparisons between studies. It is suggested that eutectic and metallic PCMs, sol-gel encapsulation methods, complex coacervation methods, and spray drying are the areas that can be further investigated for better microcapsule performance, higher microcapsule yield, and improved synthesis conditions. In the future, bifunctional microcapsules, copolymer encapsulation, and doped high-performance materials are highly promising developments when compared with current monofunctional capsules with pure polymer shells.