▎ 摘　　要

A top-down method was developed for producing colloidal dispersions of graphene sheets. Graphite nanosheets comprising hundreds of carbon layers were dispersed and gently ball-milled to exfoliate into graphene in a variety of organic solvents. After 30 hours of the shear-force-dominated grinding and a subsequent 4000 r.p.m. of centrifugation, single-and few-layer graphene sheets were readily prepared and homogeneously and stably suspended in the good solvent medium which possesses a surface tension value close to 40 mJ m(-2), such as in N,N-dimethylformamide, at a concentration up to 0.08 mg ml(-1), achieving a yield higher than 32.0 wt%. The graphene materials in the colloidal suspension were characterized using scanning and transmission electron microscopy and atomic force microscopy.