Flow rate monomer

Glow discharge or "cold" plasmas are gaining increased currency for the deposition of novel and potentially valuable macromolecular coatings. The range of properties attainable by a plasma-polymer is wide, and depends critically on such variables of the plasma deposition process as choice of monomer, substrate temperature (T ), power density (p), the excitation frequency (v), and others incluSing monomer flow rate, reactor geometry, etc... Control over these variables can produce crossllnked, dense deposits which adhere tenaciously to... 

Solutions of Eqns. 32 through 35 on an analog computer are shown in Fig. 6 for the case of polymerization in a closed system. The plots of rp(t) and p(t) are seen to be in qualitative agreement with the experimental observations shown in Fig. 7. The model of polymerization kinetics was also found to provide curves of rp versus discharge current density and monomer flow rate which were consistent qualitatively with the experimentally observed results. 

Fig. 8. Calculated and experimental rates of polymer deposition as a function of monomer flow rate [after Tibbitt et al. >]...

How the starting molecules are fragmented into activated small fragments depends on the energy level of the plasma and the nature of the monomer molecules. This is a reason why plasma polymers possess different chemical composition when the plasma polymerization is operated at different conditions, such as different monomer flow rate, RF power, and pressure of the reaction chamber, even if the same starting materials are used for the plasma polymerization. 

The fragmentation process depends on how much electrical energy (RF power) is supplied to maintain the plasma, how much monomer is introduced into the plasma, and where the monomer molecules interact with activated species of the plasma. Yasuda proposed a controlling parameter or W/FM value, where W, F, and M are RF power [J/s], the monomer flow rate [mol/s], and the molecular weight of the monomer [kg/mol], respectively [21]. The W/FM parameter is an apparent input energy per unit of monomer molecules [J/kg] therefore, the magnitude of the W/FM parameter is considered to be proportional to the concentration of activated species in the plasma. The polymer formation rate (polymer deposition rate) increases by increasing the W/FM parameter in the operational condition, whereby... 

Fig. 4 Domains of polymer deposition. W, F, and M are RF power, the monomer flow rate, and the molecular weight of the monomer, respectively...

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... 

Figure 8.1 Dependence of deposition rate of plasma polymer of tetramethyldisiloxane on discharge wattage at various monomer flow rates (cm /min).

The peak becomes sharper as the monomer flow rate (consequently the system pressure) increases. 

Figure 9.12 Infrared spectra of plasma-treated NaCl powder under various monomer flow rate conditions (TOW), F(C2F4) (cm /min) for each spectrum is as follows A, 0.1 B, 0.15 C, 0.27 D, 0.51 E, 0.86.

Figure 11.6 Dependence of internal stress in VpMDSO plasma polymers on (a) arc current, (b) Ar flow rate, and (c) monomer flow rate, 750 seem, 4.0 A arc current.

Figure 11.7 compares the effect of monomer flow rate on the internal stress for different monomers. Figure 11.7a shows the internal stress dependence... 

Figure 11.10 FTIR spectra of vinylpentamethyldisiloxane (VpMDSO) plasma polymers prepared by cascade arc torch at monomer flow rate of (a) 1 seem and (b) 40 seem 750 seem argon, 4.0 A arc current.

In LCVD, the simplest parameter that can be correlated with the flow rate of monomer is the polymer deposition rate, which is generally and most logically expressed by (mass)/(area)(time). As long as the dependence of polymer deposition rate on monomer flow rate is sought for a given monomer only, the monomer flow rate given by seem can be used without difficulty when such a correlation is extended to different monomers and the polymer deposition characteristics are compared, however, the flow rate based on cubic centimeters per minute cannot be used because the mass of a mole of gas depends on the molecular weight of the monomer. The polymer deposition rates of various monomers should be compared on the basis of the mass flow rate otherwise, polymer deposition rates are not directly proportional to the polymerization rates. 

If the polymer deposition rate is compared on the basis of monomer flow rate in cubic centimeters (STP) per minute (i.e., F rather than Fw), there is an obvious dependence on the molecular weight of monomer, as depicted in Figure 12.6. The use of normalized deposition rate, (Deposition Rate)/FM, takes care of this situation as described in Chapter 5. 

The plasma operating conditions performed in the study are summarized in Table 19.1. The monomer flow rates were determined by measuring the system pressure increase over the given time interval from the isolation of vacuum pump and then converted to flow rate (seem). Each reactor volume was measured by gas expansion method small size = 557 cm, medium size = 1278 cm, and large size = 2357 cm. (The measured reactor volume includes the volume of connecting tubes beyond the center part glass tube.)... 

An LCVD system is somewhat similar to a gas flame in which the combustion rate and the gas flow rate establish a steady-state flame. In an LCVD system, the monomer flow rate and the polymer formation rate establish a steady-state polymer-forming luminous gas phase. This situation is expressed schematically in Figure 20.17, where (a) indicates the diffusional transport of the energy-carrying... 

The solid circles represent the deposition rate obtained at a vapor pressure of 60 mtorr (the initial pressure) and the open circles at a vapor pressure of 40 mtorr. In these experiments, the system pressure was not controlled independent of monomer flow rate. The lower pressure was obtained by a lower flow rate. At the latter vapor pressure, glow does not penetrate into the 5-mm constriction and no polymer deposition occurs within the constriction. This is due to the increased gas-wall collisions that quench the luminous reactive species. 

Monomer Flow rate (seem) Power (W) Pressure (mtorr) Thickness (A) Pjl X 10 H2 Permeability ratio a (H2/CH4)... 

Fig. 11 illustrates how well the thickness growth rate, GR/FM, in 40 kHz and 13.5 MHz glow discharge of methane and n-butane, can be expressed as a function of the composite energy input parameter W/FM. Regardless of the mass of monomer, flow rate, and... 

The effect of monomer flow rate on the film appearance is similar. At low flow rates (high polymerization rate), particles are buried inside the film. As the flow rate is increased, both the size and the density of the particles decrease to yield a smoother film. 

---