Chain scission is involved in the formation of many of these groups, leading to a progressive reduction in the average molecular weight and finally to the production of CO, CO2, and H2O. In addition to oxidative degradation, there will also be direct degradation by ion-induced sputtering. These changes can have dramatic effects on the surface energy and functionality of polymer materials. Both dielectric polymer and conductive substrates can be treated with this method as illustrated in Figure 2. With nonconducting polymer films, the grounded roller is covered with a dielectric insulating material and a linear electrode is used. However, with conductive metallic substrates, the process is simply reversed by using a rotating electrode covered with a dielectric insulating material to prevent short-circuiting to ground. In either case, the electrode is always connected to a source of high voltage power, and the roller always remains grounded. However, the corona is a shower of arcs or sparks and each discharge point has the capability of causing localized damage and is difficult to apply consistently on three-dimensional components or structures. With corona treatment the effect on many materials is reported to be short-lived. This can represent a problem in some packaging applications where treatment stability is important.