Low-energy ion scattering (LEIS) study of the ageing of oxygen-plasma-treated high-density polyethylene (HDPE) surfaces

Static low-energy ion scattering (LEIS or ISS) and x-ray photoelectron spec troscopy (XPS) are used to study the surface of high-density polyethylene ( HDPE) that has been modified by exposing it to a 'cold' oxygen plasma. The HDPE surface composition is monitored by both techniques as a function of t ime after the plasma treatment. With LEIS, large differences in ageing are observed between a sample that is exposed to air after the plasma treatment and a sample that is not exposed to air, but rather kept under vacuum. The hydrophobic recovery of the sample exposed to air is very large, whereas n o recovery is observed on the other sample. The XPS measurements also show a decrease in oxygen concentration as a function of time for the sample tha t was exposed to air, but not as steep as in the LEIS measurements. The dif ferences between the air- and vacuum-exposed samples are explained in terms of differences in composition and cross-linking in the surface region. Sta tic LEIS seems to be a promising method to study the ageing of plasma-treat ed polymers. Copyright (C) 2000 John Wiley & Sons, Ltd.