Review on thermochromic materials: development, characterization, and applications

Thermochromism and thermochromic materials research and development are of great interest because of their importance in versatile applications with respect to energy-efficient building structures, textile industries, thermal or heat storage, antique maintenance processing and sensors. In general, thermochromic materials have been classified into four categories including inorganic, organic, polymeric, and hybrid systems, based on their unique material properties and operating conditions. Thermochromic materials have been prepared via different physicochemical techniques with some of them combined to maximize the yield, stability, and efficiency of the prepared TCMs. Pristine TCMs often undergo severe degradation when exposed to various external stimuli including UV irradiation from sunlight and ambient environmental conditions such as temperature, pressure, and humidity variations. Such degradation causes property and physical behavioral changes in TCMs. Various microencapsulation procedures and coating techniques are utilized to enhance the thermochromic performance of the materials and to protect the core TCMs from the degradation. Many desirable candidate materials have been developed, and extensive metrological tools have been deployed to understand the structural, morphological, microstructural, thermal, chemical, surface, and interfacial characteristics of these TCMs and their microencapsulated variants. The potential applications of the microencapsulated TCMs in industrial, commercial, and residential sectors are briefly discussed in this review paper. The future looks bright for the development of novel microencapsulated TCMs possessing nanostructural derived properties that can be effectively used in inks, paints, and coating agents for sustainable energy efficiency and many other applications.Graphical abstractEnhanced energy efficiency of buildings with smart coatings of microencapsulated TCMs