Cao Changhong, Mukherjee Sankha, Howe Jane Y, Perovic Doug D, Sun Yu, Singh Chandra Veer, Filleter Tobin
Department of Mechanical and Industrial Engineering, University of Toronto, 5 King's College Road, Toronto, Ontario M5S 3G8, Canada.
Department of Materials Science and Engineering, University of Toronto, 184 College Street, Toronto, Ontario M5S 3E4, Canada.
Sci Adv. 2018 Apr 6;4(4):eaao7202. doi: 10.1126/sciadv.aao7202. eCollection 2018 Apr.
Despite promising applications of two-dimensional (2D) materials, one major concern is their propensity to fail in a brittle manner, which results in a low fracture toughness causing reliability issues in practical applications. We show that this limitation can be overcome by using functionalized graphene multilayers with fracture toughness ( integral) as high as 39 J/m, measured via a microelectromechanical systems-based in situ transmission electron microscopy technique coupled with nonlinear finite element fracture analysis. The measured fracture toughness of functionalized graphene multilayers is more than two times higher than graphene (16 J/m). A linear fracture analysis, similar to that previously applied to other 2D materials, was also conducted and found to be inaccurate due to the nonlinear nature of the stress-strain response of functionalized graphene multilayers. A crack arresting mechanism of functionalized graphene multilayers was experimentally observed and identified as the main contributing factor for the higher fracture toughness as compared to graphene. Molecular dynamics simulations revealed that the interactions among functionalized atoms in constituent layers and distinct fracture pathways in individual layers, due to a random distribution of functionalized carbon atoms in multilayers, restrict the growth of a preexisting crack. The results inspire potential strategies for overcoming the relatively low fracture toughness of 2D materials through chemical functionalization.
尽管二维（2D）材料有着很有前景的应用，但一个主要问题是它们容易发生脆性失效，这导致断裂韧性较低，在实际应用中引发可靠性问题。我们表明，通过使用断裂韧性（积分值）高达约39 J/m的功能化石墨烯多层膜可以克服这一限制，该值是通过基于微机电系统的原位透射电子显微镜技术结合非线性有限元断裂分析测得的。功能化石墨烯多层膜测得的断裂韧性比石墨烯（约16 J/m）高出两倍多。还进行了类似于先前应用于其他二维材料的线性断裂分析，发现由于功能化石墨烯多层膜应力 - 应变响应的非线性性质，该分析不准确。实验观察到功能化石墨烯多层膜的裂纹止裂机制，并确定其为与石墨烯相比具有更高断裂韧性的主要因素。分子动力学模拟表明，由于多层膜中功能化碳原子的随机分布，组成层中功能化原子之间的相互作用以及各层中不同的断裂路径限制了已有裂纹的扩展。这些结果激发了通过化学功能化克服二维材料相对较低断裂韧性的潜在策略。
