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Chapter 6 – Production of Few Layer Graphene in Aqueous Media for Biological Studies 6.2.3.1. Stability of dialysed dispersions The concentrations of the graphene dispersions were calculated from the absorbance at 660 nm using the Beer-Lambert law (𝛼 - 4632 mL mg-1 m-1). In order to check the dialysed dispersions follow this 𝛼 value, separate dispersions of FLG/NMP and FLG/DMF were dialysed to 0.1 v/v% of organic solvents. The data obtained after vacuum filtration, drying and weighing of the graphene films fall on the linear fit observed for all other preparations (see Figure 4.3), suggesting the 𝛼 - 4632 mL mg-1 m-1 holds good for dialysed graphene dispersions. One important observation of Figure 6.3 is the drop in concentration of the dialysed dispersions compared to the starting dispersions (100 v/v%). This drop can further seen in Table 6-1 and in the highlighted regions of Figure 6.4. For the G/DMF dispersions, the concentration dropped by ~40 % during the 100 v/v% 10 v/v% dialysis. In the subsequent steps, the concentration dropped ~11 % and ~20 % for 10 v/v%1 v/v% and 1 v/v%0.1 v/v% dialysis steps, respectively. G/NMP dispersions showed similar behaviour (Figure 6.4b and Table 6-1). The drop in concentration could be attributed to a combination of the following: 1) Aggregation and sedimentation of the graphene sheets during the dialysis process. 2) Dilution within the dialysis bag. As mentioned in section 4.1.6.2, during the dialysis procedure, the dialysis bag expands slightly resulting in dilution. Despite the tight knots, the expansion of the bag could not entirely be avoided. Figure 6.4: Sedimentation behaviour of starting and dialysed graphene dispersions over 38 days. Concentrations were calculated from UV-Vis absorbance at 660 nm. Highlighted region show the drop in concentration during dialysis. 167PDF Image | PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES
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