Interaction Mechanisms Between Ar–O2 Post-Discharge and Stearic Acid I: Behaviour of Thin Films
Résumé
Interactions between a late Ar–O2 post-discharge and thin films (~1 − 2 μm) of stearic acid (SA), a C17 aliphatic chain with as end-group a carboxylic acid function, are studied. Thin films grown by evaporation are made of separated droplets and are efficiently etched by the post-discharge to get a clean surface after treatment. The dewetting of the droplets during the first minutes of the treatment leads first to a more homogeneous film in thickness which is etched until isolated islands appear and progressively shrink as a function of time. The etching of the SA occurs via C–C bonds scission when peroxide or hydroperoxide compounds are synthesized from radicals initiated by reaction with atomic oxygen from the post-discharge. A strong functionalization by OH groups grafted on the aliphatic skeleton of the SA is also observed. C = O formation is observed for longer treatment times possibly due to oxidation of OH grafted on the aliphatic chain or to a modification of the branching ratio of the C–C bond scission mechanism due a temperature rise. The acid functional group is likely not modified by the treatment.