The low-pressure plasma technique, as well as the atmospheric pressure plasma technique is suited for surface modification. Both are being used at the Institute for Manufacturing Technical Science and Applied Research (IFAM) in Bremen, Germany. Principally the processes happening on the surface are in both cases the same; whereby the effects obtained at the surface divide themselves in the categories of cleaning, activating and coating.
The cleaning of substrate surfaces (polymer, metal, glass, ceramic) in plasma is mostly to remove small residues of organic substances in connection with one with a different carried out coarse cleaning procedure. One of this kind purification will be reached in that the surface will be exposed, i.e. to an oxygen plasma; whereby, the organic substances are removed, similarly to a combustion, reacting with O2. Coarse contamination cannot be removed in plasma economically.
In the case of activation, i.e. a polymer surface will be exposed to a plasma, which either consists of noble gases (rare gas) or of molecules, that are not containing any chain-forming qualified atoms (i.e. N2, O2, NH3). Through the high energy species generated in the plasma - predominantly electrons, high energy radiation, but also ions and excited species - bonds in the surface are broken and reactive positions are generated. These reactive positions (radicals) therefore can react with each other and have as a consequence an additional cross-linking in the surface region. Partially they remain preserved in the developing higher cross-linked surfaces and yield in this way an activated surface which is qualified to reactions with atmospheric oxygen. In the case of gases that are not noble gases, such as N2, O2 or NH3, single atoms or molecule fragments can be integrated into the surface effecting a change in the surface characteristics of the treated materials through the assembling of new functional groups (see picture).
Effect of an oxygen
plasma on a polyethylene surface
A polyethylene surface can contain, for example, after a treatment in O 2-plasma carbonyl, hydroxyl and other oxygen containing functional groups (illustration). Characteristic features such as adhesive bonding, bonding of lacquer, wettability and surface energy can be altered purposefully in this manner.
In contrast to this, by a coating on the substrate out of the gaseous phase, materials will be brought up in a thickness from a few nanometers up to a few micrometers. There is a multitude of plasma supported coating procedures, like, i.e. sputtering or PECVD ("plasma enhanced chemical vapor deposition").
The Fraunhofer Institute
for Manufacturing Technical Science and Applied Material Research (IFAM)
in Bremen, Germany has localized, above all, the technique of the plasma
polymerization. It is based on the fact that the process
gas production contains elements qualified to the formation of a chain
or network (carbon, silicium, sulfur). In the plasma the original gas molecules
become "shattered" into highly excited fragments, whereas the individual
fragments react one with another on an available surface and build up a
more or less strongly cross-linked layer.
Within the bounds of its function as service provider in technology transfer, IFAM offers its resources for the processing of the above-mentioned industrial questions up to series production. Our service comprises consultation, process development, sampling and industrial installation through pilot terotechnology.
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