The increasing demands of human-machine integration require stretchable electronic devices. Percolating networks of carbon nanotubes (CNTs) have potential to work as stretchable electrodes and semiconductors, since CNTs can reorient and slide under large deformation. In this work, we investigate the effect of cyclic loadings on the resistance and morphology of stretchable CNT electrodes, by combining experiment, coarse grained molecular static (CGMS) simulation, and analytical modeling. Experimentally, a CNT electrode spray-coated on the surface of a stretchable substrate is subject to cyclic stretches with the maximal strain sequentially increasing. The resistance of the electrode in both stretching and transverse directions increases during the loading, while it remains almost a constant during the unloading, forming a hysteresis between the loading and unloading. To understand the strain-dependent and hysteretic resistance of stretchable CNT electrodes, we have developed a CGMS method to simulate the morphological change of CNT networks under cyclic loadings. Then we calculate the evolution of the resistance for different CNT configurations, by modeling a network of nanotube resistances and contact resistances. We find that during stretching, the CNTs reorient to the stretching direction. As the strain increases, the nanotubes slide between each other, and the resistance of the network increases. During the unloading, the CNTs buckle due to the compression, and the resistance of the network remains almost a constant. Based on this understanding, we have further developed an analytical model to describe the evolution of the resistance of CNT electrodes under arbitrary loadings. This combined approach enables us to design stretchable CNT devices with optimized properties.
Lihua Jin, Alex Chortos, Christian Linder, Zhenan Bao, and Wei Cai, "Strain-dependent and hysteretic resistance of stretchable carbon nanotube networks (Conference Presentation)," Proc. SPIE 10165, Behavior and Mechanics of Multifunctional Materials and Composites 2017, 101650S (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 27, 2017; Published: 10 May 2017); https://doi.org/10.1117/12.2260409.5427319322001.
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