Aging effects of repeatedly glow-discharged polyethylene: influence on contact angle, infrared absorption, elemental surface composition, and surface topography

Aging effects of repeatedly oxygen glow-discharged polyethylene surfaces were determined by water contact angle measurements, infrared (IR) spectroscopy, X-ray photoelectron (XPS) spectroscopy, and surface topography determination. Glow-discharged surfaces were stored at room temperature and in liquid nitrogen for 8 days prior to the next glow-discharge (Gld) treatment. This cycle was repeated up to 13 times. Hydrophobic recovery of the polyethylene surface, as determined by contact angle measurements, became less when the number of glow-discharge treatments increased. Hydrophobic recovery was suppressed when the samples were stored in liquid nitrogen. After five glow-discharge treatments it was possible to detect the incorporation of hydroxy groups by IR spectroscopy, while XPS spectroscopy showed that repeated glow-discharge gives rise to a higher oxygen to carbon ratio and a broadening of the CIs peak, suggesting the incorporation of C-O and C=O bonds in the surface layer of polyethylene. The surface roughness of repeatedly glow-discharge-treated polyethylene remained almost unaltered in the submicrometer range (0.30-0.35 μm), although scanning electron microscopy revealed fine-grained structures for samples after a large number of Gld treatments. It can be concluded from this study that repeated oxygen glow-discharge treatments of polyethylene create more stable, hydrophilic surfaces than can be obtained with only one treatment. However, even after repeated glow-discharge treatments, polymer surface dynamics cause a small hydrophobic recovery.