Closed system plasma polymerization

Figure 4.2 Increase of system pressure during closed system plasma polymerization of TMS.

XPS Cls/Si2p ratio steadily increases with the reaction time (film thickness) by a closed-system plasma polymerization, while the ratio more or less stays at a constant level by a flow system cathodic polymerization, as shown in Figure 4.10. Such a graded ultrathin film was found to provide an excellent corrosion protection of aluminum alloy when an organic coating was applied on top of the ultrathin film [8]. 

According to this scheme of plasma polymerization of TMS in a closed system, it is anticipated that the atomic composition of the plasma polymer should continuously change with the plasma polymerization time. Figure 13.21 depicts comparison of XPS cross-section profile of C/Si ratios for plasma polymers deposited in a flow system reactor and that in a closed system reactor. The results clearly show that a closed system plasma polymerization of TMS indeed produces a... 

Fig. 13 Increase of system pressure during closed system plasma polymerization of TMS. Plasma conditions are 25 mtorr, TMS, 2 panels of aluminum alloy, DC 1000 V.

Fig. 13 depicts the change of system pressure during a closed system plasma polymerization of TMS. Fig. 14 depicts the change of gas composition during the same... 

An example of plasma copolymerization of gases is the incorporation of N2 in the plasma polymer of styrene. N2 mixed with styrene was consumed in plasma polymerization [12]. In a closed-system experiment, pressure measurement is a very useful tool for investigating plasma polymerization, particularly when the monomer used does not produce gaseous by-products. The pressure changes observed in a closed-system plasma reactor with mixtures of N2 and styrene are shown in... 

Considering the fact that the refractive index continues to increase after most of the polymerizable species are exhausted in the gas phase, DC LCVD of TMS in a closed system contains the aspect of LCVT of once-deposited plasma polymer coating by hydrogen luminous gas phase. In the later stage of closed-system LCVD, oligomeric moieties loosely attached to a three-dimensional network are converted to a more stable form, and significantly improved corrosion protection characteristics (compared to the counterpart in flow system polymerization of TMS) were found, details of which are presented in Part IV. Thus, the merit of closed-system cathodic polymerization is well established. 

These results provide extra evidence for the hypothesis of simultaneous chain growth polymerization and fluorine elimination via interaction with energetic species in the formation of plasma polytetrafluorethylene. This is also consistent with the observation that for a plasma of C2F4 confined in a closed system the pressure decreases initially to a minimum (polymerization) and then increases (fluorine elimination) producing a non-condensible gas ° . 

In contrast to this situation, the glow discharge of acetylene in a closed system extinguishes in a few seconds to few minutes depending on the size of the tube and the system pressure. This is because acetylene forms deposit and coats the wall of the reactor. In this process of LCVD (plasma polymerization) of acetylene, very little hydrogen or any gaseous species is created, and the LCVD of acetylene acts as a vacuum pump. When the system pressure decreases beyond a certain threshold value, the discharge cannot be maintained. 

Figure 4.1 Change of gas phase species in a plasma after plasma polymerization of TMS with plasma time closed system DC discharge, 25 mtorr TMS, 2 panels of Alclad 7075-T6 as electrode, DC lOOOV.

The change of luminous gas phase is buffered by the nonluminous gas phase, which surrounds the luminous gas phase, and its influence is dependent on the size of (nonluminous) gas phase and also whether a closed system or a flow system is employed. In a closed-system operation of TMS plasma polymerization, which is shown in the left column of Figure 4.3, the IG becomes the primary glow in 3 min... 

Because the pressure before glow discharge initiation does not determine the pressure under a glow discharge, it is important to find the factors that determine this parameter. As far as the gas phase is concerned, the plasma polymerization in a closed system can be described as... 

These data clearly indicate that the same factor, which is not included as an operational parameter, has an important role at the beginning of plasma polymerization in a closed-system reactor and in a flow system. That is the change of gas phase on the inception of discharge or the creation of luminous gas phase described in Chapter 3. This factor is further influenced by the extent of adsorption or condensation of gas on the surface before discharge is initiated, i.e., the condensability of monomer and the gas mixing time have significant influence on the initial deposition rate. 

In contrast, DC cathodic polymerization in a closed system seems to be the most efficient way to operate plasma deposition in a large IVD reactor. In such a... 

In order to explore the possibility of efficiently operating plasma deposition in an industrial IVD reactor, DC cathodic polymerization of TMS in a closed system mode under conditions similar to the IVD operation was investigated. The corrosion protection properties of the plasma coatings obtained under such operation were also studied on IVD Al-coated A1 alloys. 

It should be pointed out that excellent primer adhesion was also obtained with TMS plasma polymers from a (TMS-bAr) mixture in a closed reactor system. This result indicated that, to achieve equally good primer adhesion, TMS polymerization with subsequent Ar plasma treatment could be replaced by one process of cathodic polymerization of a (TMS-bAr) mixture. Since the addition of argon to TMS can help stabilize the gas discharge, plasma polymerization of a (TMS + Ar) mixture is very important in the practical operation of plasma deposition process in conjunction with the industrial IVD process. Plasma polymerization of a mixture of TMS and argon in a closed system also has the advantage of being more... 

DC cathodic polymerization of TMS mixed with argon improved the primer adhesion performance of the closed system TMS plasma polymers. Moreover, the addition of a certain amount of argon into the TMS plasma system further increased the plasma coating quality, reflected in the increase in refractive indices. Based on the higher compatibility with the IVD process, the excellent adhesion performance, and the benefit of one process combining TMS plasma polymerization and the postdeposition plasma treatment, DC cathodic polymerization of TMS mixed with argon in a closed system is being considered as a more realistic and favorable approach in practical applications. 

When monomer vapor is introduced into the reaction system, some monomers will be adsorbed or sorbed by a porous substrate. The partition between vapor phase and sorbed phase is dependent on the adsorbing capability of a porous substrate. For instance, when a porous glass tube is used as a substrate, nearly 100% of the monomer fed into a closed system is adsorbed, and it is difficult to establish a steady-state flow of monomer vapor until the substrate is saturated with the monomer, which takes several hours at the flow rates generally used in plasma polymerization. 

In a batch operation, substrates are placed in a reactor, and plasma polymerization coating is carried out as a unit operation. Repeating the same operation treats a large number of substrates. The batch processing is the primary mode for nearly all laboratory-scale operations. The batch processing can be done in a closed system or in a flow system. Because the number of molecules in a reactor under low pressure is small, it is often necessary to use a flow system to obtain a sufficient amount of coating. 

In a continuously operated flow system, those factors associated with a closed system or a batch-operated flow system mentioned above are virtually eliminated except at the very beginning of the operation. Therefore, the reproducibility of plasma polymerization obtained by continuous operation is superior to that obtained by the batch operation. 

The Incorporation of metals Into polymer films produced by plasma techniques Is an attractive prospect since It can be envisaged that careful choice of the metal and organic phases, and close control of the overall composition of the product would greatly extend the scope of these plasma polymerized materials In, for example, electrical, magnetic and optical applications. In a previous paper (1) we have outlined a convenient method for the preparation of such materials derived from fluorinated monomers by simultaneous chemical plasma etching and polymerization in the same system. 

Tubular blood-contacting polymeric materials were modified by plasma polymerization and evaluated in animals (baboons) with respect to th r c iadty to induce acute and chronic arterial thrombosis. Nine plasma polymers based on tetrafluoro-ethylene, hexafluoroethane, hexafluwoethane/H, and methane, when deposited on silicone rubber, consumed platetets at rates ranging from l.l-5.6x 10 platelets/on day. Since these values are close to the lower detection limit for this test system, tl plasma polymers were considered relatively nonthrombogenk. Thus, artificial blood tube made of polyesters, having the inner side coated with plasma-pcrfymerized tetra-fluoroethylene, is now commercially available. 

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