Thermochromic and tunable emissivity properties of BCG/CaCl2/PEG-g-CDA composites for smart adaptive camouflage in visible and infrared wavebands

BCG/CaCl2/PEG-g-CDA composites with different mass ratios of BCG and CaCl2 under constant PEG-g-CDA were synthesized via liquid-phase reaction method. The composites were analyzed and characterized using FT-IR, XRD, DSC and UV-vis. The results show that the color changes visibly from green to yellow by improving temperature from 50 °C to 62 °C, and turns back to green reversibly with temperature cooling back to room temperature. The infrared emissivity values increase rapidly at the temperature range of 50 °C-62 °C, and the maximum variation reaches 0.23. Furthermore, the mechanisms for thermochromic phenomenon and tunable infrared emissivity were also proposed. The reversible thermochromic phenomenon is attributed to the molecular structure transformation of BCG between ring-opened quinone structure and ring-closed lactone structure. The tunable emissivity at different temperatures is ascribed to the changes of resistivity under temperature fluctuations. Our results suggest that BCG/CaCl2/PEG-g-CDA composites are a potential candidate for smart adaptive camouflage in visible and infrared waveband.