In the modified hummers method, the first step is to add Graphite to sulfuric acid and let it stir for some time, lit. mentions this step causes the graphite to swell...
I would like some details about exactly what causes the swelling, and whether temp plays any role in the swelling, basically any details on the swelling process...
I'd appreciate any input from experienced ppl as well as if there are any publication discussing this step in detail
When graphite is treated with such oxidizing media, there is surface and bulk oxidation as well as a phenomenon called intercalation, in which electrolyte/ions get inserted into the layers of graphite. This is what causes the swelling such that, the regular d-spacing of graphite (interlayer distance), can increase. Actually, it is the intercalation that helps separate the individual oxidized graphite layers to form graphene oxide which is subsequently reduced to reduced graphene oxide.
The intercalation of sulfuric acid into graphite in the presence of an oxidizing agent leads at first to the formation of graphite bisulfate C24n + m HSO4– + n H2SO4
It contains both sulfate anions and solvating acid molecules, which cause swelling of the graphite.
This reaction was described eg in:
http://download.springer.com/static/pdf/0/art%253A10.1007%252Fs11176-005-0191-4.pdf?auth66=1427795906_3bafd714c5eeaff433eea4f93422c020&ext=.pdf
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