Transparent elongation and compressive strain sensors based on aligned carbon nanowalls embedded in polyurethane

Highly extensible transparent composite materials comprised of maze-like vertically aligned carbon nanowalls embedded perpendicularly into a polyurethane film were used as strain tensors and tested by an electrical resistance method in the course of extension, extension/relaxation and compression/expansion cycles. The maze-like carbon nanowall networks with wall-to-wall average distances of 100, 200 and 300 nm were formed on SiO2-coated Si substrates by a plasma-enhanced chemical vapor deposition system. Afterwards, the nanowall network was embedded into a stretchable polyurethane matrix which enabled a high deformation of the composite. The measured extensibility of the composite was over 440 %, and its resistance increased with the extension. The sensitivity of the detection of extension, which was evaluated by the gauge factor, increased over 2000. These sensor properties can be readily tuned by varying distances of nanowalls within the network. Finally, thanks to their optical transparency in the visible light region and thermoelectric properties, these composites offer a wide range of further practical applications. (C) 2020 Elsevier B.V. All rights reserved.