Graphene exhibits diverse potential applications in oil exploration. For example, the losses of the fluid to the surrounding rock are decreased by adding platelets of graphene oxide to a common water-based drilling fluid; microscopic flakes of graphene can form a thinner and lighter filter cake. Grain boundaries (GBs) in graphene are stable strings of pentagon-heptagon dislocations. The GBs have been believed to favor an alignment of dislocations, but increasing number of experiments reveal diversely sinuous GB structures whose origins have long been elusive. Based on dislocation theory and first-principles calculations, an extensive analysis of the graphene GBs is conducted and it is revealed that the sinuous GB structures, albeit being longer than the straight forms, can be energetically optimal once the global GB line cannot bisect the tilt angle. The established atomic structures closely resemble recent experimental images of typical GBs. In contrast to previously used models, the sinuous GBs show improved mechanical properties and are distinguished by a sizable electronic transport gap, which may open potential applications of poly-crystalline graphene and will be technologically promising to enable graphene devices with logic operation in functional devices.
