Cohering particles via weak electromagnetic waves for highly conductive polymer composites

Highly electrically conductive polymer composites are fundamental materials for today's electronic engineering. However, these composites are very expensive since heavy loading of costly conductive particles (fillers) is required to guarantee high electrical conductivity. This work successfully reports that weak electromagnetic waves (EMWs) could cohere the microparticles to optimize conductive networks for highly conductive polymer composites. Such an EMW strategy arises from the earliest EMW detector (coherer) invented by Marconi and Popov in 1895 via the breakdown of surface oxides and cohering of the micro-conductors by EMWs. The flexible composite (metal microfiber-polymer) shows a unique insulator-conductor transition with drastic resistance change (50 MΩ to 1 kΩ) under weak EMWs (power: 10^-6 mW). The EMW strategy is extremely rapid (0.34 µs) and highly stable (10⁴ cycles). Such EMW effect universally describes the interactions between EM fields and composite materials that are suitable for general conductors (e.g., carbon- and metal-fillers) and most polymers.