Fig. 4.

Stiffening of GO films by soft porous sheets. a Elastic moduli of mixed multilayer films with various fractions of 5-h-etched GO. Error bars represent SD. b Representative stress–strain curves of a pristine GO film and another with 10 wt% of 5-h-etched GO. Dashed lines represent the calculated elastic moduli of the films. These results revealed an intrinsic dilemma for pristine GO sheets that prevents them from continuously conformal stacking. c First, GO sheets are easily wrinkled or folded during processing, which disrupts the packing of neighboring sheets. d Second, even if wrinkle-free sheets tightly stack, they form platelets that are drastically more rigid, and less compliant, preventing for further conformal packing. Both c and d result in architectural defects (red circles) in the multilayer films, which would become stress concentrators to degrade the overall mechanical properties. Thus, the much softer porous GO sheets effectively serve as a binder, allowing more compliant packing in the multilayer films, leading to higher stiffness