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.

Films of poly(ethylene terephthalate) (PET) have been subjected to a low frequency (70 kHz) helium discharge, with a non-symmetrical configuration of electrodes, in order to study the treatment conditions for which the 'ageing' effect is slowed down. Treatments were made for different gas flow rates (40, 70 and 100 sccm) and different exposure times (1, 10 and 30 s). Emission spectroscopy and mass spectrometry were used to characterize the discharge plasma. The resulting modifications to the polymer surface were analysed via contact angle measurements and the XPS technique. It is pointed out that treatments on an He discharge induce both a functionalization and a cross linking of the uppermost layers of the polymer film. The residual oxygen, which partially originates within the polymer, induces surface oxidation. The cross-linked content critically depends on the residence time and concentration of implicated species. It seems that a change in the surface work function takes place as a result of a surface restructuring in the earliest stages of the reactions. This could involve an increase in the rate constant for the surface de-excitation of the helium metastables in the presence of the polymer. A contribution to the understanding of the competitive processes of cross linking and functionalization, as a function of the helium flow rate, is accomplished.

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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.

Poly(ethylene terephthalate) (PET) has desirable qualities for medical application but it is a nonpolar material (γ p s = 0.6 dyn/cm) which results in its high interfacial tension with blood plasma ( γ SL = 50 dyn/cm). Modifications of the surface free energy components of PET by ion-beam treatments were investigated. Also the surface morphology of the treated PET by scanning electron microscopy was revealed. The influence of such modifications on biocompatibility of these materials was investigated by subcutaneous implants in rats.