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

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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.