Plasma monomer feed

When -xylene is used as the monomer feed in a plasma polymer process, PX may play an important role in the formation of the plasma polymer. The plasma polymer from -xylene closely resembles the Gorham process polymer in the infrared, although its spectmm contains evidence for minor amounts of nonlinear, branched, and cross-linked chains as well. Furthermore, its solubiUty and low softening temperature suggest a material of very low molecular weight (15). 

As the power input is increased (at a given flow rate), the domain of plasma polymerization approaches the monomer-deficient one, which can be recognized by the asymptotical approach of D.R. value to a horizontal line as the power input increases. In the monomer-deficient domain, the deposition rate (plateau value) increases as the flow rate is increased and shows a linear dependence on the monomer feed-in rate at a given discharge power and the system pressure (Fig. 8.2), i.e.,... 

Figure 11.6c shows the monomer feed rate dependence of internal stress in VpMDSO plasma polymer films at different argon flow rates. The overall values of internal stress in plasma films obtained with argon flow rate at 1500 seem are much higher than those obtained at 750 seem. 

From Figure 11.6c it can also be noted that the internal stress in CAT polymers deceased with increasing VpMDSO monomer feed rate. In plasma deposition process, when the other plasma parameters are kept the same, the increase of monomer feed rate indicates that the same amount of energy input is consumed by a larger number of monomer molecules. In other words, when the other plasma parameters are kept constant, the increase of monomer feed rate will actually reduce the relative energy input in plasma polymerization process. 

Figure 11.7 Monomer feed rate dependence of internal stress in plasma polymers 750 seem Ar, 4.0 A arc current.

The tubular-type plasma reactor system used in the study consists of a reactor chamber, power supply, monomer feed, and pumping-out units, as depicted in Figure 19.1. One side of the glass tube is connected to a monomer inlet and the other side to a vacuum pump with O-ring joints. A radio frequency power generator of 13.56 MHz is coupled to two capacitive copper electrodes, which are 1 cm wide and 6 cm apart. The radio frequency power was controlled by an L-C matching network and monitored by power meter. 

In a capactlvely coupled system the flow rate into the plasma is not known as precisely as for the systems described above. This is because not all monomer feed must drift into the inter-electrode gap. On the other hand the flow into the gap cannot be obtained from the knowledge of the fraction of reactor volume the inter-electrode gap represents, because the plasma polymerization process acts as a pump. 

Figure 11. Plot of apparent conversion of monomer feed to plasma polymer at the electrode and substrate vs. RF power...

Figure 12. Plot of apparent conversion of monomer feed to plasma polymer at the electrode and substrate vs. AF or AC current. Symbols on the abscissa with arrows pointing down indicate negative deposition rates. Those with arrows pointing up and down indicate both negative and positive deposition rates at the electrode. No conversions were calculated for such cases.

Plasma polymerization is usually carried out in a low pressure glow discharge sustained by either a dc or an ac electric field. Examples of the reactors used for this purpose are shown in Fig. 1. The simplest configuration involves a pair of circular parallel plate electrodes mounted inside a glass bell jar. The lower electrode usually serves as the substrate holder and is sometimes heated or cooled. Monomer is introduced through a feed tube and unconsumed monomer and gaseous products are withdrawn through a port in the base plate. 

B. Flow Rate and Pressure. As shown above the pressure will affect the location and extent of active zones in the plasma. The pressure in a plasma is controlled by pumping rate of plasma reaction products, feed rate of monomer and the number of gaseous reaction product molecules generated per monomer molecule,, Y. For a flow system (no plasma) the... 

---