Many interesting properties of 2D materials and their assembled structures are strongly dependent on the lateral size and size distribution of 2D materials. Accordingly, effective size separation of polydisperse 2D sheets is critical for desirable applications. Here, we introduce flow field-flow fractionation (FlFFF) for a wide-range size fractionation of graphene oxide (GO) up to 100 μm. Two different separation mechanisms are identified for FlFFF, including normal mode and steric/ hyperlayer mode, to size fractionate wide size-distributed GOs while employing a crossflow field for either diffusion or sizecontrolled migration of GO. Obviously, the 2D GO sheet reveals size separation behavior distinctive from typical spherical particles arising from its innate planar geometry. We also investigate 2D sheet size-dependent mechanical and electrical properties of three different graphene fibers produced from size-fractionated GOs. This FlFFF-based size selection methodology can be used as a generic approach for effective wide-range size separation for 2D materials, including rGO, TMDs, and MXene.

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