Flexibility Of Graphene Oxide And Its Electronic And Optical Properties Under Bending

With the rapid development of science and technology,wide usage of electronic products increases the demand for flexible transparent materials.Currently,due to the good conductivity and transmittance,indium tin oxide is the standard material in traditional industries.However,it is hard to satisfy the requirements of flexible devices due to the brittleness.In recent years,many new flexible conductive materials emerge,such as metal nanowires,carbon nanotubes,and graphene.Among them,graphene with ultrahigh flexibility is promising in various fields including the energy,electronics and medicine.On the other hand,graphene oxide,as a precursor to produce graphene,also shows excellent flexibility.Then,is the graphene oxide more flexible than graphene? This is still under debate between simulations and experiments.To clarity this debate,employing density functional theory,we studied the flexibility of graphene oxide in terms of bending modulus and systemically discussed the effects of group type and coverage and bending direction.The results show that the flexibility of graphene oxide is quite tunable.Graphene oxide can be either more flexible or more stiff than graphene,depending on the structural details and bending direction.Different types of functional groups enable graphene oxide different bending moduli.Hydroxyl groups present stronger enhancement of bending modulus than epoxy groups.Meanwhile,the bending modulus of graphene oxide monotonously changes with the increase of group coverage.The bending modulus of graphene oxide can continuously increase or decrease from its graphene limit,depending on the group type and bending direction.Particularly,during bending graphene oxide,the O?H hydrogen bonds can transform into O–H covalent bonds at a critical bending curvature.In addition,the electronic and optical properties of graphene oxide under bending are also briefly discussed.To summarize,our results reveal the tenable flexibility of graphene oxide and clarify the debate on the flexibility between the graphene and graphene oxide,which are useful to design graphene-based flexible devices.