Plasma polymerization domains

In a previous section, the effect of plasma on PVA surface for pervaporation processes was also mentioned. In fact, plasma treatment is a surface-modification method to control the hydrophilicity-hydrophobicity balance of polymer materials in order to optimize their properties in various domains, such as adhesion, biocompatibility and membrane-separation techniques. Non-porous PVA membranes were prepared by the cast-evaporating method and covered with an allyl alcohol or acrylic acid plasma-polymerized layer the effect of plasma treatment on the increase of PVA membrane surface hydrophobicity was checked [37].The allyl alcohol plasma layer was weakly crosslinked, in contrast to the acrylic acid layer. The best results for the dehydration of ethanol were obtained using allyl alcohol treatment. The selectivity of treated membrane (H20 wt% in the pervaporate in the range 83-92 and a water selectivity, aH2o, of 250 at 25 °C) is higher than that of the non-treated one (aH2o = 19) as well as that of the acrylic acid treated membrane (aH2o = 22). 

Another promising area for polymer development, as alluded to by Tirrell [5], is microelectronics. Plasma polymerization can be used to produce a polymeric coating directly on a substrate changing the composition of the gas feed allows a wide variation in the chemical composition of the surface produced [32], The same technique can also be used to modify surfaces for other applications, such as to improve the blood compatibility of biomaterials. The essential processes occurring in a plasma—mass transfer and reaction kinetics—have long been the domain of chemical engineers. 

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... 

In order to find the domain of LCVD, it is necessary to compare various vacuum deposition processes chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma chemical vapor deposition (PCVD), plasma-assisted CVD (PACVD), plasma-enhanced CVD (PECVD), and plasma polymerization (PP). All of these terms refer to methods or processes that yield the deposition of materials in a thin-film form in vacuum. There is no clear definition for these terms that can be used to separate processes that are represented by these terminologies. All involve the starting material in vapor phase and the product in the solid state. 

It is also important to recognize the domain in which a plasma polymerization is carried out under a given set of operational conditions. The value of WjFM alone does not identify whether a plasma polymerization is in the energy-deficient or the monomer-deficient region. A crude estimate of the domain might be made by the parameter WjFM)la( if the value of a were known for the reactor. The following conditions can be used for this purpose ... 

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.,... 

Plasma polymerization is system dependent, and a monomer does not yield a well-defined polymer that can be identified by plasma polymerization. Plasma polymers formed at the high WjFM end of the power-deficient domain as well as in the monomer-deficient domain are tight three-dimensional amorphous networks, that do not contain discernible functional groups (type A plasma polymers). 

In plasma polymerization, the dependence of the deposition rate on the operating condition varies based on the domain of the plasma polymerization as described in Chapter 8. There are three domains energy-deficient domain, transitional domain, and monomer-deficient domain. They are classified based on the dependence of the normalized deposition rate, DjFM, on the normalized energy input parameter, WjFM, where D is the deposition rate. 

Since the energy density would be different according to the relative distance from the electrodes, the different domains of plasma polymerization could exist along the... 

These data clearly show that the size of reactor is an important factor to be considered in dealing with data obtained by a reactor. The change of reactor size influences the overall performance of LCVD of a monomer, and consequently the description of operating conditions such as flow rate, system pressure, and discharge wattage cannot be used in a generic sense, unless the size factor of reactor, domain of plasma polymerization, and the relative position of the substrate with respect to the core of luminous gas phase and/or to the tip of glow could be identified. These data show the complicated system-dependent nature of LCVD, particularly that a monomer does not produce a polymer and that the externally operative parameters, such as W, p, and F, are not the actual parameters that control LCVD. 

The (TMS 02) plasma-modified polymers were made considerably more hydrophilic with average cos 0D,a,i= 0.654 (Op,a,i =49.2 11.7) but remain in the domain of amphoteric surface, under the conditions of plasma polymerization used. (TMS + O2) plasma-deposited films were slightly more dependent on the nature of the conventional polymer substrates. This is probably due to the fact that substrate polymers have different oxygen plasma susceptibilities. 

PPD Purified protein derivative PPME Polymeric polysaccharide rich in mannose-6-phosphate moieties PRA Percentage reactive activity PRD, PRDII Positive regulatory domain, -II PR3 Proteinase-3 PRBC Parasitized red blood cell proET-1 Proendothelin-1 PRL Prolactin PRP Platelet-rich plasma PS Phosphatidylserine P-selectin Platelet selectin formerly known as platelet adctivation-dependent granule external membrane protein (PADGEM), granule membrane protein of MW 140 kD (GMP-140)... 

The significance of LCVD is in the unique aspect of creating a new surface state that is bonded to the substrate material particularly polymeric material. The new surface state can be tailored to be surface dynamically stable. However, caution should be made that not all LCVD films fit in this category. Appropriately executed LCVD to lay down a type A plasma polymer layer creates surface dynamically stable surface state. In the domain, in which surface dynamic instability is a serious concern in the use of materials, a nanofilm by LCVD is quite effective in providing a surface dynamic stability, and other methods do not fare well in comparison to LCVD. 

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