Plasma activation of polymers is a current technology to increase the surface reactivity of this type of materials. The incorporation of functional groups by plasma surface activation is normally checked by X-ray photoemission Spectroscopy (XPS), while the effect of the surface activation is determined by measuring the water contact angle on the surface of the modified polymers. Aging effects, typical for this type of processes, are characterized by a recovery of the water contact angle with time an by the loss of the functional groups incorporated onto the surface as a result of the plasma activation.
Most works dealing with this type of studies look to the formation of the functional groups on samples that have been treated "ex-situ". This means that they have already lost a given concentration of surface functional groups. In the present work we have studied the plasma surface activation of PET (polyethylene tereftalate) and LDPE (low density polyethylene) by XPS, water contact angle measurements and AFM. Low pressure microwave plasmas of Ar/O2 and Ar/CO2 mixtures generated with a surfatron device were used for the surface activation of the polymers. They were then studied as a function of the aging time by XPS ex-situ, AFM and wetting angle measurements. In parallel, the same polymers were subjected to a surface activation process "in-situ" in the XPS spectrometer. For this study an oxygen atom source attached to the pre-chamber of the XPS spectrometer was used. Differences and similarities between the two types of activation processes based on the analysis of the XPS, AFM and the wetting angle evolutions permit to attribute the observed effects to either changes in surface topography or to the formation and stabilisation of functional groups on the polymer surfaces.
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