Flexibility And Optical Properties Of Graphene Derivatives Under Bending

Benefiting from the development of flexible electronic technology,flexible electronic devices continue to enter our daily life.Flexible electronic devices have a wide range of applications in flexible display,energy storage,medical treatment and other fields due to their unique ductility,high efficiency and low cost.In recent years,many novel flexible conductors have been reported,such as metal nanowires,carbon nanotubes,graphene,graphene oxide.Graphene,as a promising flexible material,has been widely used in many fields,such as energy,electronics and medicine.Usually,graphene is fabricated by chemical vapor deposition,where defects like vacancy,line defects,pentagons and heptagons inevitably occur.Defects can affect the mechanical properties of graphene.For example,pentagon-heptagonal defects can either enhance or weaken the in-plane strength of graphene.So,how about the flexibility of graphene allotropes with pentagons and heptagons compared with graphene? In addition,as a flexible electronic material,graphene oxide shows tunable flexibility and electronic conductivity.How will the optical transmittance of graphene oxide change under bending?Here employing first-principles calculations,we carried out two studies.One is to study the flexibility of the planar graphene allotropes containing pentagons and heptagons by evaluating the bending modulus.The planar graphene allotropes show superior flexibility to graphene.The bending moduli of planar graphene allotropes depend closely on the geometry and bending direction.Compared with pristine graphene,incorporation of pentagons and heptagons will change the bond length,planar carbon density and geometric contribution of carbon atoms,which further degrades the bending modulus of graphene allotropes.Moreover,the longer the average bond length is,or the smaller the planar carbon density and geometric contribution of the hexagons are,the lower bending modulus will be.Meanwhile,bending direction depended bending modulus suggests the mechanical anisotropy of the graphene allotropes.Our calculations not only provide a general approach to understand the flexibility of graphene allotropes,but also give an important clue to design high-performance flexible devices.The other work is to study the effect of bending on the optical properties of graphene oxide with different functional groups,including the light absorption coefficient,refraction index,reflectivity and optical transmittance.The results show that both bending and hydrogen bond transition can affect absorption,refraction and reflection.In particular,a new absorption peak appears at 5 e V when O…H hydrogen bonds transform to covalent bonds.Although bending and hydrogen bond transition will degrade the optical transmittance,the optical transmittance at 550 nm is still over 92% for the three graphene oxide modes studied,suggesting the high transmittance of graphene oxide under bending.These results are useful for structural analysis and applications of graphene oxide in flexible transparent devices.