Highly flexible, stretchable, wearable, patternable and transparent heaters on complex 3D surfaces formed from supersonically sprayed silver nanowires

Here we demonstrate a scalable production process for a highly transparent, flexible, patternable, and wearable heater using a single-step supersonic kinetic spraying technique that deposits silver nanowires (AgNWs) on rollable substrates, facilitating a roll-to-roll process. AgNWs were suspended in an aqueous solution and supersonically sprayed onto a rolling substrate to produce a flexible heater film without use of any binders or additional post-process treatments. Because of the high-speed impact, the intersections of the nanowires were fused, thus creating a junction-free network of nanowires, which significantly reduced the contact and thus the sheet resistance. Cyclic temperature testing confirmed the thermal stability of the AgNW heater. A heater bent to a radius of less than 2 mm was tested for 600 000 cycles; the heater exhibited little change in the sheet resistance. Moreover, it does not experience significant thermal expansion, which would manifest itself in buckling, and thus such heaters do not buckle during operation. AgNWs were sprayed onto a complex surface of a replica of Venus de Milo and Jeju's Dol Hareubang statues, demonstrating the deposition capability onto a 3D surface. Defogging and defrosting tests showed potential applications of this heater in smart mirrors or windows. The highest heating temperature of 160 °C was achieved in a transparent fibrous film having 95% transparency and 15 Ω sq⁻¹ sheet resistance at a supplied voltage of 8 V. Because the film fabrication method is rapid and scalable with the installation of multiple nozzles, the method is commercially viable.