However, this has not been well described in the literature when using a top-down exfoliation synthesis approach. For instance, several laboratories have attempted to reach this goal either by oxidising the GO flakes to different extent and/or using different starting graphite materials , or by performing sonication followed by several separation techniques. These techniques rely on the physical deposition of GO flakes depending on their lateral dimensions and thickness, which can be naturally obtained by density gradient ultracentrifugation and membrane ultrafiltration , or by altering the chemical environment with the addition of acids and organic solvents, which ultimately change the colloidal stability of GO flakes in aqueous dispersions .