Deposition of plasma-polymerized

An important and well studied example is the deposition of plasma-polymerized fluorinated monomer films [35], Monomers are fluoroalkyls, fluorohydroalkyls, cyclo-fluoroalkyls, as well as unsaturated species. The actual... 

Figure 34.20 The influence of different substrate hollow fibers on (a) air enrichment factor, and (b) air flux of composite membranes prepared by deposition of plasma polymerization coating of 1,1,3,3-tetramethyldisiloxane.

Such layers are usually made of highly cross-linked material and show good adhesion to the substrate. Examples of such membrane surface treatment are plasma polymerization of allyl alcohol and allyl amine (Gancarz et al. 2002, 2003). It was shown that the membranes modified with allyl amine do not foul as intensively during UF of the BSA solutions compared with the unmodified membranes. Similar behavior was also shown for membranes modified by the deposition of plasma-polymerized n-butylamine however, in this case, the modified layer deposited on the manbrane surface was not as enriched in amines as the polymer formed from aUyl amine (Gancarz et al. 2002). 

Oxygen Gas Barrier PET Films Formed by Deposition of Plasma-Polymerized SiOx Films... 

The XPS survey spectrum of a 75 nm thick film of plasma polymerized acetylene that was deposited onto a polished steel substrate is shown in Fig. 18 [22]. This film consisted mostly of carbon and a small amount of oxygen. Thus, the main peaks in the spectrum were attributed to C(ls) electrons near 284.6 eV and 0(ls) electrons near 533.2 eV. Additional weak peaks due to X-ray-induced O(KVV) and C(KLL) Auger electrons were also observed. High-resolution C(ls) and 0(ls) spectra are shown in Fig. 19. The C(ls) peak was highly symmetric. 

Positive SIMS spectra obtained from plasma polymerized acetylene films on polished steel substrates after reaction with the model rubber compound for times between zero and 65 min are shown in Fig. 44. The positive spectrum obtained after zero reaction time was characteristic of an as-deposited film of plasma polymerized acetylene. However, as reaction time increased, new peaks appeared in the positive SIMS spectrum, including m/z = 59, 64, and 182. The peaks at 59 and 64 were attributed to Co+ and Zn, respectively, while the peak at 182 was assigned to NH,J(C6Hn)2, a fragment from the DCBS accelerator. The peak at 59 was much stronger than that at 64 for a reaction time of 15 min. However,... 

The number of attempts to model the kinetics of plasma-polymerization has been limited thus far. Nevertheless, these efforts have been useful in demonstrating the role of different processes in initiating polymerization and the manner in which the physical characteristics of the plasma affect the polymerization rate. It is anticipated that future modeling efforts will provide more detailed descriptions of the polymer deposition kinetics and thereby aid the development of a better understanding of the interactions between the physical characteristics of a plasma and the chemistry associated with polymer formation. 

In the process of plasma polymerization, a highly crosslinked polymer is deposited on the surface The deposited plasma polymer changes the surface properties of the substrate dramatically. It modifies the surface of powders in terms of surface energy, functional groups, wettability, interaction with polymers, and dispersion... 

The most extensive studies of plasma-polymerized membranes were performed in the 1970s and early 1980s by Yasuda, who tried to develop high-performance reverse osmosis membranes by depositing plasma films onto microporous poly-sulfone films [60,61]. More recently other workers have studied the gas permeability of plasma-polymerized films. For example, Stancell and Spencer [62] were able to obtain a gas separation plasma membrane with a hydrogen/methane selectivity of almost 300, and Kawakami et al. [63] have reported plasma membranes... 

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... 

Any chemical reaction that yields polymeric material can be considered polymerization. However, polymerization in the conventional sense, i.e., yielding high enough molecular weight materials, does not occur in the low-pressure gas phase (without a heterogeneous catalyst). With a heterogeneous catalyst, polymerization is not a gas phase reaction. Therefore, the process of material deposition from luminous gas phase in the low-pressure domain might be better represented by the term luminous chemical vapor deposition (LCVD). Plasma polymerization and LCVD (terms explained in Chapter 2) are used synonymously in this book, and the former... 

The terms luminous chemical vapor deposition and plasma polymerization are used synonymously in this book. Dealing with mechanism of reactions that lead to formation of solid deposition, PP is used according to the traditional use of the term. When dealing with the formation of reactive species and other operation and processing aspects, LCVD is preferentially used. 

In the chain growth free radical polymerization of a vinyl monomer (conventional polymerization), the growth reaction is the repeated reaction of a free radical with numbers of monomer molecules. According to the termination by recombination of growing chains, 2 free radicals and 1000 monomer molecules leads to a polymer with the degree of polymerization of 1000. In contrast to this situation, the growth and deposition mechanisms of plasma polymerization as well as of parylene polymerization could be represented by recombinations of 1000 free radicals (some of them are diradicals) to form the three-dimensional network deposit via 1000 kinetic... 

In discussions of the mechanism of plasma polymerization appearing in the literature, polymerization, particularly the growth mechanism of polymer formation, is dealt with in a somewhat vague manner without any clear distinction between mechanism of polymerization and mechanism of polymer deposition. For instance, the hypothesis that plasma polymerization occurs via the polymerization of adsorbed monomer on the surface invokes the location of polymer formation rather than mechanism of polymerization that is, the mechanism of polymerization, whatever that would be, is intuitively or a priori assumed. Nevertheless, such a hypothesis constitutes an important school of thought in dealing with the polymerization mechanism. 

In parylene polymerization, the thermal cracking of the dimer (starting material) creates monomeric diradicals. All starting materials are converted to the reactive species, i.e., diradicals. No specific initiator for the chemical structure of starting material is formed. The situation is close to that of plasma polymerization. The comparison of plasma polymerization and radiation polymerization, and the comparison of the two vacuum deposition polymerizations (parylene polymerization and plasma polymerization) enable us to construct an overall view of material formation in the luminous gas phase. 

So far as the growth mechanism is concerned, parylene polymerization is the closest kin of plasma polymerization. It is advantageous to go into a little details of parylene polymerization in order to understand how vacuum phase deposition of material occurs starting from a vapor phase material. 

Highly reactive (unstable) and nonselective species tend to react with any surface on which the species strike and form a polymer deposition with a high level of bonding or adhesion to the surface. Because of this aspect, plasma polymerization tends to form a thin film with a good adhesion with various kinds of substrate materials. Because of nonselective reactivity, the reactive species of plasma polymerization have poor penetration into small cavities such as those of porous structures. Reactive species tend to react with wall material at the entrance of a cavity rather than penetrating into the cavity (which requires that the species not react with the wall at the entrance). 

The deposition rate of plasma polymerization depends on many experimental factors of glow discharge. A large number of attempts have been made to correlate the polymer deposition rate with such operational variables as flow rate, discharge power, current density, and system pressure. Although reasonable agreement is found... 

As already pointed out, the temperature dependence of polymer deposition is not related to the conditions of plasma polymerization (i.e., the flow rate and... 

Because of the chemical structure insensitive (nonspecific) nature of plasma polymerization illustrated above, the structure of the monomer appears to have relatively little influence on the polymerization characteristics as well as on the characteristics of plasma polymers. This is largely true in the context of selective reactivity due to the chemical structure of monomers in conventional polymerization (i.e., monomer vs. nonmonomer). However, the influence of monomer structure, as classified by five types in Table 7.2, is actually accentuated when the operational conditions are varied. In this context, therefore, the chemical structure of a monomer is a key factor in its deposition characteristics and also in determining the properties of the deposition. 

Another important and unique feature of plasma polymerization is the incorporation of gases that do not form polymer or solid deposits in plasma by themselves during polymer formation of organic molecules in plasma. This incorporation of gases is plasma copolymerization and not the trapping of gas molecules in plasma polymers. 

The normalized deposition rate is the only form of deposition rate that can be used to compare deposition characteristics of different monomers with different chemical structures and molecular weights under different discharge conditions (flow rate, system pressure, and discharge power). Similarly, WjFM can be considered as the normalized power input. When only one monomer is employed, D.R. can be used to establish the dependency of deposition rate on operational parameters. Even in such a simple case, D.R. cannot be expressed by a simple function of W or F, and its relationship to those parameters varies depending on the domain of plasma polymerization. 

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.,... 

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