Polymer surface modification by ion implantation and reactive deposition of transparent films

The use of polymeric materials is often limited by low hardness, poor wear resistance and wettability considerations. The area of mechanical changes caused by ion beam treatments has been explored only to a limited extent for polymers despite their growing usage in automotive, biomedical and aerospace applications, in which traditionally metals have been used. Polycarbonate (PC) specimens were subjected to medium-high energy (160 keV) nitrogen ion implantation at different dosage. Ion irradiation, even at low fluence, can improve surface properties in a well controlled way. A colour change from amber to dark brown with increasing fluence is associated with the ion implantation process. Hardness and elastic modulus, as measured by a nanoindenter, increase dramatically with increasing N dose. The surface property improvement can be explained by cross-linking phenomena, responsible for the formation of a three-dimensionally connected rigid network. Such hypothesis is confirmed by TOF-SIMS analyses of untreated and ion bombarded specimens. Too high implanted fluence may induce progressive degradation of the PC surface. Should the thickness of the ion-modified layer be too low for a specific application, it is possible to extend the ion irradiation treatment by plasma or ion beam assisted deposition of hard semi-transparent top layers. Using such a method the advantages of both the techniques can be retained to obtain PC surfaces with optimum wear resistance properties. (C) 1998 Elsevier Science S.A.