ABSTRACT:In this work, the surface treatment of poly(ethylene terephtalate) (PET) films in a low frequency (70 kHz) discharge in helium-oxygen mixtures is investigated. Optical emission spectroscopy and mass spectrometry are used to analyze the gas phase. Surface properties are analyzed via the X-ray photoelectron spectroscopy (XPS) technique and contact angle measurements. The treatment conditions are optimized in order to obtain a surface functionalization, which would show a reduced ageing effect. The stability of the treated surface via the crosslinking process seems to be closely correlated to the presence of the helium metastable species in the discharge. A very good stability with the ageing time is obtained for samples treated in gaseous mixtures that contain less than 5% O 2 , conditions for which the oxidized polymeric structure seems to be formed on a reinforced crosslinked layer. The very efficient loss of He excited species, for amounts of O 2 higher than a few percent, affects the surface crosslinking. For high quantities of oxygen introduced in the reactor (more than about 50%), a balance is established between the introduction of oxygenated groups and the ablation of the surface. In this case, the surface degradation has, as a consequence, the ageing effect.
A method for the direct measurement of the impedance of the oscillatory circuit which determines the character of certain self-sustained (natural) oscillations in a dc discharge is described. The results show that the impedance corresponds to an oscillatory parallel circuit with lumped constants.
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