Plasma polymerization, reactive coatings

Highly reactive (unstable) and nonselective species involved in plasma polymerization coating tend to... 

On the other hand, coating techniques do have less influence on the fibre surface. Nevertheless, brittle coatings such as SiC deteriorate mechanical properties of the fibres. As an example, reactive sputtered SiC layers improve the interfacial shear strength of carbon fibre reinforced epoxy resin /3/. Recently, Dagli and Sung 141 reported about the coating of carbon fibres by plasma polymerization of acrylonitrile and styrene using an inductively coupled plasma. 

FIG. 7 shows the pH dependence of the non-dispersion interactions Wg (determined by the two-liqid-method with liquid 1, cyclohexane and liquid 2, water) for coated Hercules carbon fibres. One of the carbon fibres was coated in a benzene/air plasma, the other in a benzene/ammonia plasma. Both reactive gas components added during the plasma polymerization process influence the term Ws in a similar way. This may be caused by the consecutive reactions between the plasma polymers and atmospheric oxygen due to the high concentration of free radicals on the film surface. This explanation is in accordance with the results of IR analysis. 

Several studies have presented the results of plasma polymer characterization by various techniques 3 - s - 52 such as i.r., wettability, and adhesion characteristics. The wettability properties of plasma-polymerized styrene films were dependent upon the degree of incorporation of N into the film. Severe polymerization conditions (high power, low pressure) resulted in a reduction in aromaticity of PP films. The electrical properties of certain plasma polymers were reported. Experiments to optimize coating parameters for the continuous coating of a moving substrate have been carried out. The reactivity of plasma polymers... 

PECVD causes the reactive gases to decompose and enhance chemical reaction rates of the precursors via the electrical discharge rather than via thermal heating. This allows films to deposit at lower temperatures than CVD. The lower temperatures also allow for the deposition of organic coatings, such as, plasma polymers. Usually, the operational pressures in these systems are 0.1-10 Torr, the plasma density in PECVD discharges is 10 -10" cm and the ionization degrees are 10 -10 [6]. The process is also often referred to as plasma polymerization. PECVD/plasma-polymerization processes are performed both at low and atmospheric pressure, as described later. 

Despite the fact that plasma polymerization leads to rigid and laterally homogeneous films, a varying number of pinholes is observed in most cases [118]. Pinholes are crucial defects when the plasma polymer serves as a coating for reactive metals. In this case, electrolyte can penetrate through these channels to the uncovered metal surface and give rise to localized forms of corrosion. Not surprisingly, the ultrathin plasma polymers contain several pinholes or intrinsic channels that can be located by immersion of the coated sample in a copper sulfate solution... 

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