Thickness dependence of mechanical properties of free-standing graphene oxide papers

We have characterized thickness dependence of mechanical properties, such as Young's modulus, fracture strength, fracture strain and toughness, of graphene oxide papers using tensile and bulge test methods. The GO papers were made from Hummer's method and the fabricated GO paper's thickness varied from 0.1 $\sim$ 100 $\mu$m. The measured Young's modulus and fracture strength decreased with increasing thickness ranging from 44.6 $\sim$ 8.5GPa and 170.2 $\sim$ 40MPa respectively. Through TEM, SEM and AFM characterization, the inner structure and surface morphology such as crack formation and roughness change are the keys to the variation of mechanical properties in the GO papers by the thickness. The thicker GO papers are weaker because it has more manufacturing voids in it that cause it to fail easily and less stiff. Surface wrinkle and residual stress are the mechanism of terraced fracture strain.