Reversible Thermochromic Phase Change Material Microcapsules With High Latent Heat via Cellulose Nanocrystal Stabilized Pickering Emulsion for Smart Coatings

Abstract Thermochromic (TC) smart coatings are promising for temperature indicator and anti‐counterfeiting. However, it is still a big challenge to fabricate multifunctional TC coatings with sustainable materials by facile approaches. Herein, reversible TC phase change material (PCM) microcapsules with high latent heat, stability, rapid color‐response, and tunable color‐changing temperature are facile prepared via cellulose nanocrystal (CNC) stabilized Pickering emulsion. The mixture of crystal violet lactone (CVL), bisphenol A (BPA) and PCM is used as the three‐component TC material and oil phase of Pickering emulsion. Methyl behenate (MB) and coconut oil (CO) are selected as PCMs due to their excellent solubility for CVL/BPA, Pickering emulsifying ability by CNCs, and appropriate phase change temperature (PCT). The obtained TC‐PCM microcapsules showed outstanding anti‐leaking stability, significant thermal energy storage and release capacity (200.2 J/g and PCM content of 89.0% for TC‐MB), and fast color change in seconds. The color‐changing mechanism is analyzed by density functional theory. The TC‐PCM microcapsules displayed blue color below PCT and turned to white above PCT, which are about 55 and 15 °C during heating for MB and CO. The applications of TC‐PCM microcapsules as smart temperature‐responsive color‐changing coatings are also demonstrated for decorative coating, temperature indicating, information encryption, and anti‐counterfeiting.