Graphite Surface Fluorination by PTFE Plasma Sputtering

The fluorination of expanded graphite sheets using polytetrafluoroethylene (PTFE) Ar plasma sputtering was investigated. The graphite sheet was exposed to Ar plasma between two PTFE sheets. The content of fluorine and oxygen at the graphite surface was correlated as a function of plasma treatment power and temperature with the nature of water wettability and surface potential (SP). The fluorine content increased with increasing power and temperature, resulting in increased hydrophobic nature. Water wettability and the electrical nature of the front of the sheet in contact with Ar plasma differed greatly from those on the back of the sheet: the front was more hydrophobic when power was changed, but more hydrophilic when temperature was changed. The SP value for the front became negative, nearly independent of power and temperature. The back still exhibited a positive SP value, the same as an untreated sheet.