Cold plasma treatment: Surface or bulk modification of polymer films?

Reactive species of nitrogen cold plasma could interact with a polymeric surface, leading to an important surface functionalization (mostly as amino group attachment) and consequently to a surface having a Lewis base character. Under certain conditions, the surface functionalization is not the only modification; a morphologic transformation is also noticed. The virgin isotactic polypropylene is composed in bulk of smectic and amorphous phases in the same proportions, and after the plasma treatment a more organized monoclinic a phase appears. During the plasma treatment, two types of crystallization take place, smectic phase --> a phase and also amorphous --> smectic phase, their respective proportions varying in the thickness of the film. This phenomenon could be explained by an absorption of the plasma VUV radiations by the polymer film. Illustration is given with different plasmas for which the VUV emission is important.