Applications of plasma-polymerized

Plasma polymers of certain kinds of monomers have very little, if any, internal stress, and thickness is not a limiting factor of application. However, because of this very feature such polymers may not provide certain coating functions that are sought for the application of plasma polymerization. In other words, the internal stress is not a drawback of plasma polymer but an important characteristic of the materials formed by LCVD. 

In certain applications of plasma polymerization, the incorporation of electrode material, particularly in a controlled and designed manner, is extremely useful and becomes a great asset in LCVD. For instance, a thin layer of plasma polymer of methane with a tailored gradient of copper has been shown to improve the adhesion of the thin layer to a copper substrate as well as the adhesion of metal to a polymer film [3,4]. In general applications of LCVD, in which the metal contamination should be avoided, it is important to select the electrode material that has low sputtering yield. Titanium has been used successfully in such cases. 

It has been generally observed that polymer deposition occurs mainly on a surface exposed to glow. More precisely, the deposition rate of polymer onto a surface that does not make contact with glow is several orders of magnitude smaller than that onto a surface that contacts glow. The results outlined here clearly demonstrate that the rate of deposition of a polymer onto a surface that contacts glow is dependent on the S/pV of the glow. This factor seems to have important implications in the application of plasma polymerization, which may involve substrates of various sizes and shapes. 

The twenty chapters included in this volume can be conveniently divided into the following groups review plasma polymerization of hydrocarbons plasma polymerization of fluorocarbons plasma polymerization of organometallic systems plasma-initiated polymerization and applications of plasma polymerization. Though the emphasis of this Symposium is on the fundamental aspects of plasma polymerization, we should not lose sight of the fact that it is the potential applications of this technique that has stimulated the efforts in basic research. Potential applications for plasma-polymerized films include membranes for reverse osmosis, protective coatings for optical components, and insulating layers for semiconductors. 

I. Some Specific Applications of Plasma-Polymerized Film Deposition... 

Table 1. Potential applications of plasma-polymerized films...

Since this is the first review of PP to appear in this series it is appropriate to begin with a brief description of the technique and the characteristic features of its products. The remainder of the review is divided into four sections kinetic and mechanistic studies of plasma polymerization, product and plasma characterization, applications of plasma polymerization to achieve technological goals (including patents), and finally plasma-induced polymerization of liquid monomers. 

A very common and useful approach to studying the plasma polymerization process is the careful characterization of the polymer films produced. A specific property of the films is then measured as a function of one or more of the plasma parameters and mechanistic explanations are then derived from such a study. Some of the properties of plasma-polymerized thin films which have been measured include electrical conductivity, tunneling phenomena and photoconductivity, capacitance, optical constants, structure (IR absorption and ESCA), surface tension, free radical density (ESR), surface topography and reverse osmosis characteristics. So far relatively few of these measurements were made with the objective of determining mechanisms of plasma polymerization. The motivation in most instances was a specific application of the thin films. Considerable emphasis on correlations between mass spectroscopy in polymerizing plasmas and ESCA on polymer films with plasma polymerization mechanisms will be given later in this chapter based on recent work done in this laboratory. 

The hydrodynamic factors that influence the plasma polymerization process pose a complicated problem and are of importance in the application of plasma for thin film coatings. When two reaction chambers with different shapes or sizes are used and when plasma polymerization of the same monomer is operated under the same operational conditions of RF power, monomer flow rate, pressure in the reaction chamber etc., the two plasma polymers formed in the two reaction chambers are never identical because of the differences in the hydrodynamic factors. In this sense, plasma polymerization is a reactor-dependent process. Yasuda and Hirotsu [22] systematically investigated the effects of hydrodynamic factors on the plasma polymerization process. They studied the effect of the monomer flow pattern on the polymer deposition rate in a tubular reactor. The polymer deposition rate is a function of the location in the chamber. The distribution of the polymer deposition rate is mainly determined by the distance from the plasma zone and the... 

The deposition of thin polymeric films from a cold plasma in a radio-frequency glow discharge apparatus has become an important means of modifying surfaces in materials applications [42], Applications receiving much attention recently have been the use of plasma polymerization to obtain biocompatible materials, and to produce functional surfaces for attachment of biologically active substances [43-45]. In this respect, many studies of protein adsorption have been... 

The purpose of this paper is to discuss some of the recent advances in our understanding of the kinetics and mechanism of plasma polymerization, the structure and properties of plasma polymers and some of their potential applications. It is not intended to be exhaustive, as earlier reviews (5-] ) are already available. Interested readers are referred to the literature cited for further details. 

Electron spectroscopy (ESCA) has been found to be particularly useful for the structural analysis of plasma polymerized film surfaces. Most of the applications are directed to fluorocarbon polymers because of the large chemical shifts in the binding energies of C(ls) electrons caused by fluorines bonded to carbon. 

Bhat, N.V. and Wavhal, D.S. 2000. Characterization of plasma-polymerized thiophene onto cellulose acetate membrane and its application to pervaporation. Sep. Sci. Technol. 35 227-242. 

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