Paper PS1-FrM9
Surface Modification of PTFE Surfaces with Post-Discharge RF Plasmas Operating at Low and Atmospheric Pressure

Friday, October 24, 2008, 11:00 am, Room 304

PTFE samples were exposed to post-discharges of RF plasma operating at low pressure (5 10-2 torr,pure O2) and at atmospheric pressure (Ar-O2). The plasma phase was characterized using optical emission spectrometry (OES). More specifically, the intensity of the O 777 nm line was chosen as a probe for the chemical reactivity of the plasma. The PTFE surface was characterized using monochromatized XPS, dynamic water contact angle, and atomic force microscopy. Depending on the power and treatment time, the surface energy could be either increased or decreased. At low power and/or treatment time, an increase in surface energy due to the grafting of oxygenated polar species is obtained. At high plasma power, a decrease in surface energy, leading, in some cases, to superhydrophobic surfaces is obtained. No oxygen is detected on such surfaces by XPS, and the superhydrophobic behaviour is attributed to an increase in roughness, as evidenced by AFM. By changing the position of the sample in the low pressure system, we could discriminate the role of the electrons, and the one of atomic oxygen. It is suggested that the increase in roughness is due to a chemical etching of the surface, initiated by high energy electrons, and terminated by the formation of gaseous products, CO and CO2, as detected by OES. A reaction mechanism is proposed. Interestingly, similar behaviours are observed using the low pressure system, and the atmospheric pressure system, in one particular geometry. The comparison between low pressure and high pressure results, on the same kind of sample, with the same type of plasma generation (RF mode) opens new routes for the understanding of surface reaction mechanisms at the atmospheric plasma – polymer interface.

This research is funded by the IAP "plasma surface interactions", from the Belgian Federal Government.