Polymerization plasma-state

The polymer formation and properties of polymers formed by glow discharge polymerization are controlled by the balance among plasma-induced-polymerization, plasma state polymerization, and ablation. 

In a flow system plasma polymerization, the system pressure is continuously adjusted by controlling the opening of a throttle valve connected to the pumping system. Because of fragmentation of original monomer in a plasma state, the composition of gas phase changes on the inception of the plasma state. The increase in the total number of gas molecules is compensated by the increased pumping rate in a flow system, and a steady-state flow of a consistent composition of gas phase is established at a predetermined system pressure. 

Plasma state polymerization is an atomic process, which occurs only in a plasma state. This type of polymerization can be represented by the statements... 

In plasma state polymerization, the polymer is formed by the repeated stepwise reaction described above. It should be noted that plasma-induced polymerization does not produce a gas phase by-product, because the polymerization proceeds via the utilization of a polymerizable structure. The process can be schematically represented by tiie following chain propagation mechanism ... 

It should be emphasized that polymerization in a glow discharge consists of both plasma-induced polymerization and plasma state polymerization. Which of these two mechanisms plays the predominant role depends not only on the chemical structure of the starting material but on the condition of the discharge. 

If a polymer is formed throu plasma-induced polymerization from tetrafluoroethylene, the ESCA Cls spectrum should be identical to that of Teflon. Therefore, the fact that the ESCA Cls peaks are significantly different from those in the spectrum of Teflon indicates that a major portion of the glow discharge polymerization is not plasma-induced polymerization. How the balance between plasma state polymerization and plasma-induced polymerization is influenced by the conditions of glow discharge and the location of polymer deposition within a reactor can be seen by comparing the ESCA Cls spectra shown in Figures 2-4. 

Because polymer formation can proceed through more than one major type of reaction, i. e., plasma-induced polymerization and plasma state polymerization, depending on the chemical structure of the monomer and also on the conditions of discharge, such as discharge wattage, flow rate, type of discharge, and geometrical factors of the reactor, the balance between polymer formation (polymerization) and ablation is for most cases extremely complicated. 

The monomer chosen is hexafluoroethane, which cannot be polymerized by plasma-induced polymerization and which cannot be polymerized in a glow discharge imder ordinary conditions presumably because the ablation process associated with the glow discharge is excessive. Attempts have been made to supress the ablation process and to shift the balance between plasma state polymerization, which is assumed to be present, and ablation. However, it has been observed that polymer formation for hexafluoroethane does occur when polyethylene is used as substrate. On the other hand, no polymer formation can be observed either with ESCA or by surface energy analysis when glass is used as a substrate. 

Plasma-Induced Plasma State Polymerization Polymerization Ablation... 

This indicates that ablation is no loiter dominant, and polymer formation prevails. This phenomenon can be explained by postulating that Hg reacts with F atoms emanating from the fluorine containing compound in the glow discharge and forms the more stable HF, which reduces the ablation in a dramatic manner. Because hexafluoroethane does not form a polymer by plasma-induced polymerization, the overall effect can be explained by the balance between plasma state polymerization and ablation. 

In the case of a non chemical-reaction plasma, the state of the plasma can be described by the electron energy distribution function, f(e) (J ). In the case of a polymerizing plasma, however, f(e) may not be sufficient. In other words, the structure of the... 

The formation of polymeric materials in the plasma state of organic vapor(s) (partially ionized state) is referred to as plasma polymerization, and the resultant materials are plasma polymers. Because the most practical way to create low temperature plasma is to employ an electric glow discharge, the terms glow discharge polymerization and glow discharge polymers are often used synonymously for plasma polymerization and plasma polymers. 

A plasma polymerization is a gas plasma initiated and/or propagated conversion of a low-molar-mass compound into a polymer. The plasma-initiated polymerization has also been called a plasma-induced polymerization and the plasma propagated polymerization is sometimes named a plasma state polymerization. The mechanism of the former is a conven-... 

Chemical or radical polymerization Electrochemical polymerization Photochemical polymerization Metathesis polymerization Concentrated emulsion polymerization Inclusion polymerization Solid-state polymerization Plasma polymerization Pyrolysis... 

In this method, the plasma state is only used in the initial stage, to initiate the polymerization. The formed active molecules are transferred fi om the plasma phase to the monomer phase (liquid or solid), in which the chain growth reaction runs already without the plasma participation. As a result of this process one gets a conventional polymer, built of mers, which often exhibits a very high molecular weight. This method is particularly useful for the pol5merization of water-soluble monomers such as acrylamide and its derivatives. 

Strictly speaking, the ususal process of polymerization is not the same as the process that occurs in glow discharge. In this context, polymer formation in a plasma state takes place via a "nonpolymerizing" process. Thus, polymer formation of this type may be characterized as elemental or atomic polymerization in contrast to molecular polymerization, which describes the conventional process. The following discussion may illustrate the atomic nature of polymer formation in a plasma state. 

Plasma state polymerization can be represented by the following mechanisms ... 

One of the most significant differences between plasma-induced polymerization and plasma-state polymerization is the fact that plasma-state pol3nnerization produces gas phase by-products, which do not become incorporated in the polymer. This means that the components of the plasma phase change as soon as plasma-state polymerization occurs. Consequently, the influence of the product-gas plasma to the entire system is an important factor. 

Chemical alternation of the surface layer and deposition of a new layer on top of the silicone mbber can be achieved by physical techniques. For the inert surface of silicone rubber, the former requires the generation of high-energy species, such as radicals, ions, or molecules in excited electronic states. In the latter case, coatings of atoms or atomic clusters are deposited on polymer surfaces using technique such as plasma (sputtering and plasma polymerization) or energy-induced sublimation, like thermal or electron beam-induced evaporation. 

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