Innovative design of microencapsulated phase change materials for thermal energy storage and versatile applications: a review

As a class of thermal energy-storage materials, phase change materials (PCMs) play an important role in sustainable development of economy and society with a rapid increase in energy demand. Microencapsulation of solid–liquid PCMs has been recognized as a vital technology to protect them from leakage and running off and to give them a shape stability in the liquid state to offer the ease of handling and thus received tremendous attention from fundamental studies to industrial development in recent decades. Aiming to provide the most complete and reliable source of information on recent progress and current development in microencapsulated PCMs, this review focuses on methodologies and technologies for the encapsulation of PCMs with a variety of wall materials from traditional organic polymers to novel inorganic materials to pursue high encapsulation efficiency, excellent thermal energy-storage performance and long-term operation durability. We attempt to clearly summarize the selection of core and wall materials, synthetic methods, formation mechanisms and characteristic performance of microencapsulated PCMs to help scientists better understand their design principles and synthetic mechanisms. This review also highlights the diverse design of bi- and multi-functional PCM-based microcapsules by fabricating various functional shells in a multilayered or hierarchical structure to provide a great potential to meet the growing demand for versatile applications. We also provide insights on the future research and development direction of microencapsulated PCMs with multifunctional applications in energy efficiency, sustainable processes, high-tech energy management and specific physicochemical effectiveness.