**1. Introduction**

The rapid global economic growth and population explosion resulted in increased consumption of nonrenewable energy resources such as coal, petroleum and natural

gas which not only reduces these fossil fuels sources but also leads to major global environmental issues like CO2 emission, and global warming and air pollution. If the world energy requirements totally depend on fossil fuel which is continuously exhausting will results in energy crisis in the near future. To minimize the reliance on fossil fuels for energy production, the development of renewable energy resources and the enrichment of energy efficiency have been deliberated as the alternative strategy that could be adopted [1, 2]. The scientific development of thermal energy storage by utilizing phase change materials (PCMs) to store latent heat has been considered as a worthy solution for reducing the worldwide energy scarcity as these materials provide viable ways of keeping thermal energy and offering reliable energy management by controllable heat release in suitable environments [3]. PCMs are a class of heat storage materials, able to absorb and release sufficient amounts of latentheat energy at a constant temperature when a state change occurs from a solid form to the liquid one and vice-versa. In addition to higher thermal energy-storage density compared to conventional heat-storage materials, PCMs can bridge the gap between energy availability and energy use to reduce energy waste [4].

The application of PCMs as a means of thermal-energy storage has been practiced since 1970s, and PCMs have been developed and designed to fulfill the desired requirements. Nowadays, PCMs have not been only applied in renewable energy effective utilization such as solar thermal energy and low-temperature waste heat utilization but also used for thermal regulation and thermal management in the fields of photovoltaic-thermoelectric systems, temperature-sensitive electronic parts or devices requiring cool or thermal protection, biological products or pharmaceutical needing cool storage, smart fibers and textiles with a thermoregulatory function, telecom shelters in tropical regions, thermal buffering of Li-ion batteries, energysaving buildings, thermal comfort in vehicles, etc. [5].

Though PCMs due to their desirable properties is widely used in both domestic and industrial areas in recent years, their phase transition brings some difficulties during their application for thermal energy storage and management. After fusion PCMs are converted to low viscous liquids which can then easily diffuse or flow over other materials and thus cause difficulty in handling the process in the liquid state [6]. Other problems associated with the commonly used PCMs include the need of using special latent heat devices, the hysteresis of thermal response due to low thermal conductivity and supercooling, the poor heat transfer during the charging and recovery processes, absorb moisture from the atmosphere or lose water through evaporation, the leakage and loss of PCMs, etc. [7]. Due to these problems, pristine PCMs are generally not recommended for thermal energy storage applications. To avoid the problem, microencapsulation technology was introduced which involves the packing/encapsulation of PCMs into tiny closed ampules that not only protect the liquid PCMs from the interference and interaction of the surrounding materials but also give them a stable form in the liquid state. The product obtained as a result of this packing technology was named microcapsule. The microcapsules which pack the PCM core individually with a firm shell can, therefore, handle even liquids as a solid material [8]. Additionally, the development of a microcapsule shell provides a large heat transfer surface to the encapsulated PCMs and hence considerably increases the heat transfer and thermal response [9]. Thus, microencapsulation of PCMs has been accepted as a more consistent technology for liquid PCMs compare to form stable composite PCMs. Microencapsulation technology of solid–liquid PCMs has received great attention for over 20 years, and several studies can be found in the literature on this topic [10]. Usually, the microencapsulated PCMs could be prepared by making

#### *Design and Fabrication of Microencapsulated Phase Change Materials for Energy/Thermal… DOI: http://dx.doi.org/10.5772/intechopen.102806*

a polymeric shell via coacervation, in-situ polymerization, interfacial polymerization and suspension polymerization techniques, for which the commonly used shell materials include polyureas, poly (methyl methacrylate), melamine-formaldehyde resins, polystyrene, urea-formaldehyde resins, and bio-based polymers such as Arabic gum, agar and gelatin. Moreover, many inorganic materials such as titanium dioxide (TiO2), silica (SiO2), calcium carbonate and aluminum oxide have been reported in the recent literature that could also be used as shell materials for encapsulating PCMs [11–13]. These inorganic shells have shown much higher mechanical strength and rigidity than the polymeric ones and can form a much more secure barrier around PCMs to protect them from damaging interaction with the environment.

Currently, the researchers are interested in the design and development of multifunctional microencapsulated PCMs. One of the potential approaches to achieve the additional functionality involve the use of inorganic functional shell assembly on the microencapsulated PCM core. In this way, not only the additional functions for microencapsulated PCMs along with the wall materials is achieved but also allows the establishment of signal or multilayered shells with various designed functions. Pointing at the high-tech designs and versatile applications of microencapsulated PCMs for thermal energy storage and thermal management, this chapter provides a reliable source of information on recent progress and development in microencapsulation technology for solid–liquid PCMs and especially introduces the diverse designs for PCMs-based microcapsules with various special functions. Moreover, a thorough analysis of the trend in the development and applications of microencapsulated PCMs is also presented. The chapter also highlights the design of bi- and multi-functional PCM-based microcapsules by fabricating various functional shells in a multilayered structure to offer a great potential to meet the growing demand for versatile applications.
