Influence of helium-dielectric barrier discharge treatments on the adhesion properties of polyamide-6 surfaces

Due to the poor adhesion properties of polymers, the immobilization of certain species onto the polymer surface requires a pretreatment in order to increase the surface reactivity. In our experiments, a diffuse dielectric barrier discharge (DBD) in helium at atmospheric pressure has been used to improve the wettability and the adhesion properties of polyamide-6 (PA-6) films. The surface characteristics are analyzed by atomic force microscopy (AFM), contact angle measurements and X-ray photoelectron spectroscopy (XPS). The treated surfaces present a modified morphology, with an increased area compared to the untreated ones, effect which is favorable for the physical adsorption at the surface. The strong increase of the adhesion work on the treated surfaces show that new functional (hydrophilic) groups are introduced onto the surface. The surface modification takes place in less than 10 s of treatment and presents only limited reversal to the untreated state over long ageing time. The DBD treatment markedly induces an important increase of the oxygen amount at the surface, which is due both to the "cleaning" of the surface by removal of the weak cohesive layer that makes barrier with the environment and to the surface oxidation by oxygen incorporation from atmospheric air. The physico-chemical surface modifications, related with a modified morphology, an increased polarity and a higher level of surface oxidation, may be favorable to the further linkage of selected biological species relevant in medical usages. (c) 2005 Elsevier B.V. All rights reserved.