Polymer deposition, mechanism

Nanocapsules of biodegradable polymers, such as PLA and PLA copolymers or poly (e-caprolactone), have been prepared by an interfacial polymer deposition mechanism [163-166], An additional component, a water-immiscible oil, is added to the drug-polymer-solvent mixture. A solution of the polymer, the drug, and a water-immiscible oil in a water-miscible solvent such as acetone is added to an external... 

From the data shown in Table 2, one can conclude that the method of polymer deposition (mechanical mixing) before pyrolysis allows one to prepare carbosils with a greater carbon content, compared with carbosils prepared from liquid solutions of polymers and subsequent carbonization (Table 1). 

The excessive formation of powders occurs only under limited conditions, although powder formation has been observed in reactors of different designs and types of discharge and with various monomers, particularly in a specific section of a reactor that is related to the flow pattern of gas. Therefore, powder formation provides an excellent opportunity for examining the basic principles of the polymer deposition mechanism. 

Powder formation in an LCVD system is a reflection of the polymer deposition mechanism. The size and number of particles may be taken as a measure of the polymerization-deposition mechanism or the status of an LCVD system. At one extreme is exclusive powder formation, as reported by Liepins and Sakaoku [7] at the opposite extreme is the formation of a continuous film in which no visible particles can be found. Even in the latter case, however, the work of Havens et al. [12] involving the use of small-angle X-ray scattering indicates that detectable domains... 

Whilst elimination (by oxidation) or masking (by polymer deposition on the cuticular scales) are the accepted mechanisms by which shrink resistance is achieved, there is evidence that other factors need to be considered, particularly as it is possible to obtain a shrink-resist effect without degradation or masking of the scales. A review is available [310] of the mechanism of chlorine-based shrink-resist processes. 

The microstructure was realized by a dry-film photoresist technique and based on established techniques from printed circuit board technology [142], Dry resists are available as thin films, e.g. of thickness 50 or 100 pm. The resist films are encased in other polymer materials which are later removed. The resist films can be deposited on various base materials such as silicon or polymers giving mechanical stability. Lamination is carried out with a roller laminator. Then, exposure is made and spray development without any solvents follows. The process steps can be repeated at multi-laminated structures. Closed structures can be made in this way. 

Comparison of the chronoamperograms recorded during EDOT electropolymerization in the two different ionic liquids and two conventional acetonitrile-based electrolytes allows some conclusions to be drawn about the mechanism of polymer deposition of PEDOT from these different media (Figure 7.12) [80], The current transients suggest that the process is initially much slower in the solution... 

This paper describes a process for activating polyimide surfaces for electroless metal plating. A thin surface region of a polyimide film can be electro-chemically reduced when contacted with certain reducing agent solutions. The electroactivity of polyimides is used to mediate electron transfer for depositing catalytic metal (e.g., Pd, Pt, Ni, Cu) seeds onto the polymer surface. The proposed metal deposition mechanism presented is based on results obtained from cyclic voltammetric, UV-visible, and Rutherford backscattering analysis of reduced and metallized polyimide films. This process allows blanket and full-additive metallization of polymeric materials for electronic device fabrication. 

Figure 2 shows an example of polymers belonging to each of these families. Each of these polymers, their polymerization and deposition mechanisms will be discussed below. 

XPS data, on the other hand, showed that the ETC AT treatment of Ar + CF4 and Ar + C2F4 yielded just as good, if not better, fluorination of PET fibers than radio frequency plasma treatment with these gases [14,15]. These examples clearly demonstrate that polymerizable species in plasma polymerization are not photon-emitting species in most cases. This is in accordance with the growth and deposition mechanism based on free radicals, which account for the presence of large amount of dangling bonds in most plasma polymers. 

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. 

Some monomers show a more or less anticipated decrease in polymer deposition rates based on the concept that a pulsed discharge decreases the initiation rate, but some monomers show dramatically increase deposition rates. The most significant effect of pulsed discharge, however, can be seen in the concentration of dangling bonds, which reflects the unique mechanisms of material formation in LCVD. 

Other reactions also probably lead to the formation of —CF3 in the polymer, but for the simplicity of discussion, let us consider that the —CF3 formation step, regardless of the reaction mechanism, occurs on the inception of glow discharge and examine how the content of —CF3 varies with the location of polymer deposition within a reactor. 

The inclusion of particles in a film of plasma polymer was once considered by some investigators to be a characteristic problem due to the plasma polymerization mechanism, which hampers the practical use of plasma polymers in some applications. In contrast to this view, the formation of powder or the inclusion of particles in a film is related to the polymer deposition part of polymerization-deposition mechanisms. The inclusion or elimination of particles, therefore, could be accomplished by selection of the proper operational parameters and reactor design. The data of Tiepins and Sakaoku [7] are a typical demonstration that powders can be formed nearly exclusively if all conditions are selected to favor powder formation. An important point is that the monomers used in their study were those commonly used by other investigators for the study of film formation by plasma polymerization in other words, no special monomer is needed to form powders exclusively. 

Because powder formation depends on the polymer deposition portion of the polymerization-deposition mechanisms of LCVD, its dependence on operational parameters such as the flow rate and system pressure is not necessarily the same in... 

Thus, powder formation can be viewed as a polymer deposition process occurring by the same polymer formation mechanism that applies to the formation of films. In other words, no special monomer, reactive intermediate, or a different agent of polymer formation is needed for powder formation. The infrared spectra of films and powders are virtually identical [11], as shown in Figure 8.19 and Table 8.3. 

The complexity of polymer deposition, which is depicted in Figure 10.1, could be best understood by comparing corresponding schemes for other (hypothetical) mechanisms. Let us first consider a hypothetical case in which a monomer polymerizes in vacuum and deposits onto an exposed surface without any complication. In other words, if a polymer can be formed in vacuum by free radical polymerization, the polymerization mechanism can be depicted as shown in Figure 10.2. In this case, the chemical structure of a plasma polymer can be predicted from the structure of the monomer, and only unreacted monomer escapes... 

An important implication of the data obtained with both a tubular reactor and a bell jar reactor is that the polymer deposition onto a stationary substrate cannot be uniform due to the diffusional transport of polymer-forming species and the path-dependent growth mechanism. The variation of polymer deposition rates at various locations becomes smaller as the system pressure decreases because the diffusional displacement distance of gaseous species increases at lower pressure. It is important to recognize that a certain degree of thickness variation always exists when the plasma polymer is deposited onto a stationary substrate regardless of the type of reactor and the location of the substrate in the reactor. 

Because a polymer-forming luminous gas phase such as the tail-flame portion of an inductively coupled radio frequency glow discharge behaves as a fluid, the deposition mechanism can be investigated by examining the influence of the fluid mechanical aspects of luminous gas phase on the deposition rate of polymer. 

Conductive polymers may be synthesized via either chemical or electrochemical polymerization methods. Electrodeposition of conductive polymers from electrolytes is, thus, feasible provided that the depositing polymer is not soluble in the electrolyte.206 Conductive polymers can be deposited from the electrolytes containing the monomers via either electrooxidation or electroreduction, based on the monomer type used. Similar to that of metals, the electrodeposition of polymers is based on nucleation and growth. The deposition mechanism involves oxidation of monomers adsorbed on the electrode surface, diffusion of the oxidized monomers and oligomerization, formation of clusters, and eventually film growth.213... 

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