Solid-liquid phase change materials microcapsules: Synthesis strategies, thermal storage and beyond

Thermal energy storage is crucial in the context of achieving carbon neutrality. Phase change latent heat stands out among various thermal storage methods due to the high energy density of phase change materials (PCMs). PCMs possess unique characteristics such as tunable thermal storage or/and release processes, constant phasetransition temperatures, and changes in physical state. However, solid-liquid PCMs cannot be directly utilized due to the liquid leakage in their melted state. The encapsulation of PCM microcapsules (PCMMs) is essential for overcoming limitations and optimizing functionalities of the PCMs. Encapsulation strategies play a key role in considering factors like morphology, structure, physicochemical properties, and specific applications. Furthermore, PCMMs can expand their potential applications by incorporating functional nano-materials within their shells or introducing specific components into their cores during the synthesis process. This review examines various encapsulation strategies for PCMMs, including physical, physicochemical, and chemical methods. Various applications of PCMMs are summarized and analyzed with regards to the characteristics of PCMs in thermal storage, temperature control, and state transformation. Furthermore, the reinforcement strategies or/and design considerations of PCMMs are crucial for meeting specific requirements, such as conventional latent heat storage, thermal protection, and thermal-triggered intelligent materials. Finally, it discusses current challenges, proposed solutions, and future research directions in the field of PCMMs, particularly Janus particle modified PCMMs.