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DLS as an efficient characterisation technique for estimating the lateral dimensions of the graphene flakes was also explored. The πΏπ·πΏπ derived from the primary peak positions of IPSD of DLS were compared to the calculated πΏπ ππππ and πΏπ΄πΉπ. It was found that the πΏπ·πΏπ indeed exhibited a linear relationship with πΏπ ππππ and πΏπ΄πΉπ, with a relative error of ~25 % in measuring the mean size of nanosheets (in submicron region). This is consistent with the IPSD obtained from DLS is a measure of the hydrodynamic diameter, which is the diameter of a sphere whose volume is equal to that of the mean graphene flakes volume, having similar translational diffusion coefficient. 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. ο· Secondly, various techniques for producing pristine FLG in aqueous media were explored. A simple solvent exchange method like dialysis was employed to exchange the organic solvents with water in the organic solvent-exfoliated FLG dispersions. UV- Vis and 1H NMR spectroscopy confirmed that the organic solvent could be reduced down to levels of 0.1 v/v% (99.9 v/v% water) while maintaining sufficient colloidal stability. Raman spectroscopy and XRD indicated no in-plane disruptions, suggesting the pristine nature was retained in FLG. The higher absolute π values for the dialysed 0.1 v/v% FLG dispersions meant that the electrostatic repulsion was the main stability mechanism with some contribution from edge effects. TDOC, a bile surfactant effectively exfoliated graphite to highly-stable FLG dispersions with the best exfoliation conditions of 36 hr sonication and 10000 rpm centrifuge speed producing flakes with γπΏπ΄πΉπγ ~100 nm and π1β5βππ > 92 %. A one-step process of using neutral phospholipids like PC (the major component of cell membrane) to produce pristine FLG in PBS buffer was demonstrated (Exfoliation conditions: 36 hr sonication and 2000 rpm centrifuge speed). The absence of adsorbed lipid molecules on graphene surface by AFM analysis confirmed their weak interaction. The surface charge screening effect by salt results in poor stability of graphene in PBS buffer. Despite its poor stability, it was shown that PC indeed efficiently exfoliated graphite to FLG (graphene monolayers by AFM) and its pristine nature was confirmed by Chapter 8 β Conclusions and Future Works 236PDF Image | PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES
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