Plasma-generated Radicals Trapped on Glass Surface anrd Their Reactivities

Abstract

An inorganic plasma exposure with short duration of the various glass substrate such as hard (Pyrex), neutral and soft glasses, generated stable paramagnetic centers, and were all detected by ESR spectra. The identical ESR spectra were also observed by UV irradiation using low pressure mercury lamp. Thus, UV radiation around 2537Å from the plasma is responsible for these param a gnetic centers. The electronic structure of the center was presumed to be a“hole trap”of the glass substrate. It was found that these centers lacked radical reactivities but had catalytic activities to generate the radical species of surface molecules.
On the other hand, an organic plasma exposure of the same glasses under th e similar conditions as above produced an ultrathin polymer film on the glass surface in the glow region, in addition to the UV-induced paramagnetic centers. Several kinds of these films can effectively trap the plasma-generated leftover radicals, resulting in the formation of long-lived organic free radicals. The PBN spin trapping techniques demonstrated that the long-lived free radicals thus formed were highly reactive to give intense ESR spectra of the spin adducts. Thus, the glass surface treated by organic plasma exposure can be functionalized w ith high catalytic acitivities for radical reactions and used for an initiation of the radical polymerizations.