Kim Taehoon, Kim Daesik, Yoon Jaeyoung, Joo Yunsik, Hong Yongtaek
Department of Electrical and Computer Engineering and Inter-University Semiconductor Research Center (ISRC), Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 08826, South Korea.
ACS Appl Mater Interfaces. 2021 Jul 14;13(27):32307-32315. doi: 10.1021/acsami.1c08590. Epub 2021 Jun 28.
Cracks typically deteriorate the structural and electrical properties of materials when not properly controlled. A few papers recently reported the controlling methods of crack formation in the brittle materials utilizing the lateral V-notch structure. For ductile materials, however, there have been few papers reporting cracking phenomenon, but full cracking control including predesigned initiation, propagation, and termination has not been reported yet. Therefore, we report a predesigned full cracking control in ductile conductive carbon nanotube (CNT) films by introducing inkjet-printed L-shape micronotch (LMN) structures inspired by directional stamp perforation marks. In spite of the high fracture toughness of CNT films, the LMNs determine locations of initial crack formation and guide crack propagation in a predesigned way. Selective connection of isolated cracks in the CNT film increases its resistance monotonically under tensile strain and thus tremendously well maintains high linearity (adj. value > 0.99) in resistance change over record large strain ranges of 0.01-100%, which enables us to quantitatively classify strain values accurately for previously reported practical body signals for the first time. We believe that our facile printing-based crack control strategy not only provides a comprehensive solution to various stretchable sensor applications but also builds a new milestone for cracking mechanism studies in fracture mechanics.
当裂纹未得到妥善控制时，通常会使材料的结构和电学性能恶化。最近有几篇论文报道了利用横向V形缺口结构控制脆性材料中裂纹形成的方法。然而，对于韧性材料，虽然有一些论文报道了裂纹现象，但尚未有关于包括预设计裂纹起始、扩展和终止在内的完全裂纹控制的报道。因此，我们通过引入受定向印章穿孔标记启发的喷墨打印L形微缺口（LMN）结构，报道了一种在韧性导电碳纳米管（CNT）薄膜中进行预设计的完全裂纹控制方法。尽管CNT薄膜具有较高的断裂韧性，但LMN能确定初始裂纹形成的位置，并以预设计的方式引导裂纹扩展。CNT薄膜中孤立裂纹的选择性连接在拉伸应变下会使其电阻单调增加，从而在0.01 - 100%的创纪录大应变范围内，能极好地保持电阻变化的高线性（拟合值>0.99），这使我们首次能够准确地对先前报道的实际身体信号的应变值进行定量分类。我们相信，我们基于印刷的简便裂纹控制策略不仅为各种可拉伸传感器应用提供了全面的解决方案，也为断裂力学中的裂纹形成机制研究树立了一个新的里程碑。
