Yielding and flow of highly concentrated, few-layer graphene suspensions

For a wide range of applications of graphene suspensions, a thorough understanding of their rheological properties is crucial. We probe the microstructure of dense suspensions of micron-sized, few-layer, defect-free graphene platelets by measuring their viscoelastic properties at various concentrations up to 39 mg ml −1 . We propose a model to relate the yield strain to the mesh size of the microstructure as a function of volume fraction . From the yield stress measurements we infer the typical bond energy ( 20 k B T ) and dependence of the bond number density. These results allow us to express the steady shear viscosity for Peclet number Pe < 10 in terms of the platelet dimensions, bond energy and using a relaxation ansatz. We propose a simple model to explain the measured yielding behaviour of concentrated suspensions of graphene platelets which allows us to model the viscoelastic response in terms of bond energy, packing fraction and platelet dimensions.