Doctor of Philosophy
Department of Chemistry
Müller, Marc Benjamin, Chemically Converted Graphene Dispersions and Graphene Films, Doctor of Philosophy thesis, Department of Chemistry, University of Wollongong, 2011. http://ro.uow.edu.au/theses/3364
The formation of graphene dispersions and its subsequent characterisation form the basis of this thesis. A range of experimental techniques were employed for this characterisation, namely atomic force microscopy (AFM), contact angle and conductivity measurements, UV-visible spectroscopy, Fourier transform infrared spectroscopy (FT-IR), elemental analysis, pH-zetapotential, acid-base titration, and capillary zone electrophoresis (CZE). Various fabrication techniques such as layer-by-layer self-assembly and vacuum filtration were used to create thin transparent, conducting films as well as micron thick conducting paper.
Graphene dispersions were created by oxidising graphite, exfoliating graphite oxide to graphene oxide (GO) via sonication, and reducing it to chemically converted graphene (CCG) with hydrazine. CCG has been shown to be a negatively charged colloid. To avoid aggregation on reduction of GO to CCG, the hydrazine to GO mass ratio was optimised to 7:10. CZE was performed to investigate the electrokinetic behaviour of colloidal CCG in comparison to GO. The different amount of charge carrying functional groups were reflected in the slower electrophoretic mobility obtained for the CCG in comparison to the GO. CCG and GO paper were produced via vacuum-filtration of CCG and GO dispersions. The conductivity of CCG paper increased almost linearly with increasing thermal annealing temperature to a maximum 351 S/cm. A Youngs modulus and tensile strength of 41.8 GPa and 293.3 MPa respectively could be obtained.
Thin films of anionic CCG were produced by self-assembly with the cationic polymers polyethylenimine (PEI), poly(diallyldimethylammonium chloride) (PDDA), poly-L-lysine hydrobromide (PLL) or chitosan (CHIT). Up to 20 bilayers of PEI-CCG could be self-assembled with full CCG coverage per layer. The sheet resistance for a single PEI-CCG bilayer was (29.6 +/- 8.4) MOhm/square and the absorbance at 270 nm between 0.2 and 0.5.
Raman spectroscopy of self-assembled CCG, GO and thermally annealed (500°C, 1 h in argon) CCG and GO films showed a lowering in G to D peak ratio for CCG films. Annealed films showed a higher G to D peak ratio than non-annealed films. The electrochemical electron transfer properties at self-assembled PEI-CCG films were tested using potassium ferri /ferrocyanide. Reversible electron transfer chararcteristics were observed. Lastly the cytocompatiblity of PEI-CCG films was investigated. Cytocompatibility on neural, muscle, and fibroblastic cells was observed using live cell phase contrast imaging and lactate dehydrogenase (LDH) assays.