Development of multi-colored reversible thermochromic phase change materials with different color formers

In this study, a novel series of thermochromic phase change materials (TC-PCMs) with multicolor responsiveness and superior thermal energy storage capabilities were developed successfully. The monochromatic thermochromic microencapsulated phase change materials (TC-MPCMs) cores were prepared using bisphenol A as the color developer, crystal violet lactone or 6′-(diethylamino)-1′,3′-dimethylfluoran or 2′-(dibenzylamino)-6′-(diethylamino)fluoran as color former, and tetradecanol as solvent, showing blue, red and green respectively. Binary formers combinations produced purple, cyan and reddish-brown microcapsules, with cyan and reddish-brown systems showing intermediate green transition state. The microcapsules were embedded in polyvinyl alcohol/waterborne polyurethane matrices to prepare thermochromic films (TC-F), with trimesoyl chloride to modify the films' water resistance. The thermal properties, chromic characteristics, thermal stability, microstructure, mechanical properties, and surface modifications of the materials were systematically analyzed using relevant characterization techniques. The results showed that the enthalpy values of TC-PCMs, TC-MPCMs, and TC-F were around 200 J/g, 125 J/g, and 10 J/g, respectively, exhibiting favorable thermal storage characteristics. The size of TC-MPCMs decreases with increasing emulsion dosage. The mechanical properties of the TC-F decrease as the amount of TC-MPCMs added increases. The water contact angle of the modified film showed a significant increase, indicating excellent hydrophobic properties. Both TC-MPCMs and TC-F maintained execellent performance after 100 thermal cycles, demonstrating exceptional durability. Furthermore, experimental tests of TC-F as a temperature-indicating label demonstrated rapid thermochromic response during heating. Thus, this engineered material shows significant potential for applications in wearable devices, temperature sensors, and anti-counterfeiting technologies.