PENETRATION OF PLASMA SURFACE MODIFICATION .1. CF4 AND C2F4 GLOW-DISCHARGE PLASMAS

Plasma treatment of a polymeric surface could involve at least three m ajor mechanisms: (1) direct interaction of reactive species in the low -temperature plasma state with the surface (line of sight irradiation effect), and (2) chemical reactions of plasma-induced reactive species with the surface, and (3) reactions among reactive species and the su rface (plasma polymerization). The first and the third effects are con sidered to be limited to the surfaces which directly contact with plas ma (glow). The second effect is not limited to the surfaces that conta ct with plasma state but can penetrate beyond the plasma zone by diffu sion. Using an assembly of fibers, of which only the top layer contact s with plasma (glow), the penetration of chemical changes caused by pl asma exposure was investigated. Results indicate that the fluorination effect (incorporation of fluorine-containing moieties on the surface of polymeric substrate) penetrates through a considerable thickness of the assembly of fibers, depending on the porosity (gas permeability) of the system. Chemical reactions of plasma-induced (chemically) react ive but nonpolymerizing species with the substrate fibers seems to pre dominate. The direct interactions of energetic species, such as ions, electrons, and electronically excited species, with polymeric surfaces seems to play relatively minor roles in the plasma treatment investig ated. The major role of plasma, in this case, seems to be creating suc h chemically reactive species. (C) 1994 John Wiley & Sons, Inc.