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Chapter 5 β Production of Few Layer Graphene in Organic Solvents and not material type affects the value outputted by the DLS instrument. Moreover, by fitting the data, they have derived a semi-empirical correlation (Equation 5.3) between the size outputted by DLS and γπΏγ, that can be used to estimate the mean size of the dispersed nanosheets.70 γπΏγ = (0.07 Β± 0.03)π(1.5Β±0.15) Equation 5.3 π·πΏπ In the current study, by comparing the mean size data of DLS with AFM and Raman it can be said that πΏπ·πΏπ can estimate the size of nanosheets with a relative error of 25%, agreeing with Lotya et al.70 This in situ length measurement technique, despite its error, could play a crucial role when preliminary ideas of the flake sizes are required, comparing samples in a quality control environment such as production or understanding the in situ aggregation of graphene sheets. The latter will be demonstrated in Chapter 6 when considering bio surfactant-graphene dispersions. 5.3. SUMMARY In this Chapter, the production of stable dispersions of FLG in NMP and DMF by sonication of natural graphite was discussed. The concentration of the dispersion was found to increase with sonication time and decrease with centrifugation speed. Moreover, dispersions produced at higher centrifugations speeds were found to stable over six months without any visible sedimentation. The exfoliation efficiency was characterised using AFM. Longer sonication times and higher centrifugation speeds resulted in dispersions with smaller (πΏπ΄πΉπ β 80 to 120 nm) and thinner (π β 3 to 5) flakes and vice versa for dispersions produced at shorter sonication times and lower centrifugation speeds. Despite flakes having relatively small γπΏγ ~ 130 nm, samples produced at 60 hr sonication and 6000 rpm centrifugation speeds were the best of all preparations with π1β5βππ % ~80 % whilst maintaining stable dispersion. FLG/NMP and FLG/DMF prepared at the conditions were used as the starting material for dialysis in Chapter 6. Raman spectroscopy was used to understand the quality of the flakes. The Raman spectra of all the samples exhibited a symmetric 2D band and its position, FWHM(2D) along with πΌ2π·βπΌπΊ ratio indicates that the graphene is few-layer γπγ < 5) in nature. By 158PDF Image | PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES
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