A molecular dynamics investigation on mechanical properties of hydrogenated graphynes

Abstract

Graphyne, a new type of carbon allotropes, has attracted considerable attention in recent years. Using molecular dynamics simulations, we investigate the mechanical properties of four different graphynes (α-, β-, γ-, and 6,6,12-graphynes) functionalized with hydrogen. The simulations results show that hydrogenation can greatly deteriorate the mechanical properties of the graphynes. For the different graphynes with 100% H-coverage, the reduction in fracture stress depends on the percentage of acetylenic linkages in the graphyne structures: The more the acetylenic linkages, the larger the reduction. For the same graphyne, the reduction in fracture stress depends on the hydrogenation location, distribution, and coverage. Hydrogenation on the acetylenic linkages causes a larger reduction in fracture stress than that on the hexagonal rings. A line hydrogenation perpendicular to the tensile direction leads to a larger reduction in fracture stress than that when the line hydrogenation is parallel to the tensile direction. For random hydrogenation, the fracture stress and Young's modulus decrease rapidly at low H-coverage (<10%), and then level off with increasing coverage. The reduction in the mechanical properties due to hydrogenation is found to be related to the formation of weakened out-of-plane C-C bonds, which leads to earlier breaking of those bonds and subsequent fracture of the graphynes. The present study not only offers an in-depth understanding in the mechanical properties of hydrogenated graphynes and their fracture mechanisms but it also presents an important database for the design and practical applications of hydrogenated graphynes. © 2013 AIP Publishing LLC.