The effect of sonication treatment of graphene oxide on the mechanical properties of the assembled films

Graphene oxide films (GOFs) are candidates for structural materials in many applications, but their mechanical properties are frequently divergent, inconsistent, and poorly reproducible. During the fabrication of GOFs, sonication treatment of graphite oxide (GiO) has become a standard step in preparing graphene oxide (GO) solutions prior to assembly. In this work, we systematically studied the effect of sonication treatment of GiO on the mechanical properties of the final GOFs. GOF made from the initial sonication-free GiO solution has large elongation but very low fracture strength and toughness, mainly due to the inhomogeneous structures formed with the incompletely exfoliated GiO flakes. In contrast, a mild sonication within 2 min fully exfoliates the GiO flakes and simultaneously maintains a large amount of large-size GO sheets. The resulting GOF achieves a good balance of both high strength and large elongation, and hence exhibits a superior toughness (1.09 +/- 0.14 MJ m(-3)). However, when further increasing the sonication time to 10, 30, or 60 min, the mechanical properties of GOFs gradually deteriorate, primarily attributed to the significantly reduced GO sizes under intense continuous sonication. Our study provides an insight into the relationship between the sonication time of GiO and the mechanical properties of GOFs, and this knowledge may help to devise better strategies to achieve high-performance GOFs and other GO-based materials.