  Ultrasonication is widely used to exfoliate two dimensional (2D) van der
Waals layered materials such as graphene. Its fundamental mechanism, inertial
cavitation, is poorly understood and often ignored in ultrasonication
strategies resulting in low exfoliation rates, low material yields and wide
flake size distributions, making the graphene dispersions produced by
ultrasonication less economically viable. Here we report that few-layer
graphene yields of up to 18% in three hours without introduction of basal plane
defects can be achieved by optimising inertial cavitation during
ultrasonication. We demonstrate that the yield and the graphene flake
dimensions exhibit a power law relationship with inertial cavitation dose.
Furthermore, inertial cavitation is shown to preferentially exfoliate larger
graphene flakes which causes the exfoliation rate to decrease as a function of
sonication time. This study demonstrates that measurement and control of
inertial cavitation is critical in optimising the high yield
sonication-assisted aqueous liquid phase exfoliation of size-selected
nanomaterials. Future development of this method should lead to the development
of high volume flow cell production of 2D van der Waals layered nanomaterials.
