Solution-Processable, Ag-Sandwiched Nanotube-Coated, Durable (SAND) Architecture Realizing Anti-breaking Cyclic Heating on Arbitrary Substrates

We develop a solution-processable, Ag-sandwiched carbon-nanotube-coated, durable (SAND) architecture that enables power-efficient and highly consistent cyclic heating up to 400 °C at 6 V with neither structural degradation nor substrate breakage. The Ag/CNT/Ag-stacked SAND structure, comprising an airbrushed carbon nanotube (CNT) network layer sandwiched by the Ag layers reduced with ionic Ag ink coatings, can be created by a facile and scalable all-solution-processable fabrication protocol without resorting to vacuum-assisted nanofabrication. Through a systematic comparison with Ag-only and CNT/Ag- or Ag/CNT-bilayered structures, we show that the SAND architecture can improve the joule-heating efficiency and uniformity, and more importantly, the anti-breaking durability to overcome the thermal expansion discrepancy against the underlying substrate. This is analytically interpreted through a thermal stress-induced substrate breaking mechanism, where the increasing difference in the thermal expansion between the substrate and coated layers upon heating can be effectively suppressed within the SAND architecture. Readily applicable to more scalable, diverse substrates ranging from brittle glass to large-area polymer films, the SAND architecture can be utilized in the flexible and reliable anti-failure heating devices required in such applications as machine and vehicle components, sensor systems, and safety and warm-up gears.