Auger analysis of films formed on metals in sliding contact with halogenated polymers

Abstract

The transfer characteristics of polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), and polychlorotrifluoroethylene (PCTFE) sliding on metals were studied by Auger electron spectroscopy. The polymers were slid on atomically clean S-Monel at room temperature in ultrahigh vacuum, and the track of the slider on the metal was subjected to in situ Auger analysis. A discussion of the Auger spectrum of PVC showed that the chlorine was highly susceptible to electron-induced desorption and a part of it exhibited a desorption cross section of ≳10−16 cm2. This high cross section for desorption of the halogen was postulated to be a necessary condition to be satisfied by the Auger spectra of all halogenated polymers and assists in determining whether a polymer transfer film is established on the metal by sliding. It was found that a polymer transfer film was established by sliding PTFE. The film was uniform and continuous, and no buildup occurred with multiple traversals. The film thickness was estimated to be 2–4 atomic layers. A polymer transfer film was not established by sliding PVC or PCTFE. Instead, a chemisorbed film of approximately monolayer coverage was generated on the metal surface. In the case of PVC this film consisted largely of chemisorbed chlorine, whereas PCTFE may possibly have produced chemisorbed chain fragments on the metal surface. This correlates with the thermal decomposition behavior of these polymers and indicates the possibility of decomposition of the polymer surface by frictional heating.