Design and Tunability of Thermochromic Polymers Based on Dye-Developer-Solvent Systems: Toward Non-Toxic Materials

Thermochromic polymers have had significant development over the years through consistent research. Specifically, polymers that involve an embedded ternary thermochromic compound, which consists of a dye, color developer, and cosolvent, have garnered a lot of attention for the tunability of their color-changing properties. These compounds exhibit color changes through the mechanism of proton transfer between the dye and developer species, and the presence of a solvent is crucial to facilitating this phenomenon. By manipulating the type of each component within the dye-developer-solvent (DDS) compound, the color, direction of color change, and phase transition temperature can be adjusted. The fabrication of thermochromic polymers with DDS compounds can be done through encapsulation, impregnation into a porous material, coating, or a combination of encapsulation and compounding with a polymer matrix. Potential applications of temperature-sensitive polymers include temperature sensors and heat regulators in packaging, clothing, medical devices, and architecture. Research efforts are being continuously made on DDS compounds to make them safer and more eco-friendly with the replacement of conventional components with biobased materials. This review provides a comprehensive overview of the working principle of ternary thermochromic DDS compounds, the tunability of the thermochromic properties, the current progress of research on utilizing DDS compounds in polymers, and the prospects in developing nontoxic thermochromic polymers for food packaging and medical applications.