Scalable Spray-On\nFabrication Approach for Voltage-Tunable\nThermal Emissivity Surfaces

We report a new approach for fabricating gate-tunable\nthermal emissivity\nsurfaces by spraying them on graphene ink. The devices consist of\na multilayer graphene (MLG)/porous alumina membrane/gold stack, in\nwhich the MLG is deposited by spraying the graphene ink onto the porous\nmembrane using an airbrush. The graphene ink consists of μm-sized\nflakes of MLG suspended in a solution of polyvinylpyrrolidone and\nethylene glycol. The alumina porous membrane is filled with the ionic\nliquid [DEME][TFSI], forming an electrochemical cell. When a positive\nvoltage is applied to the device, the intercalation of [TFSI]<sup>−</sup> anions causes large changes in the thermal emissivity\nof the MLG. This, in turn, gives rise to a substantial change in the\napparent temperature (i.e., thermal camouflage) as measured by a thermal\nimaging (i.e., FLIR) camera sensitive over the 7.5–14 μm\nwavelength range. In this work, the apparent temperature change reaches\nΔ<i>T</i> = 14 °C. This method of spray coating\noffers a scalable solution that is compatible with roll-to-roll printing\nand manufacturing techniques.