Barrier characteristics, plasma polymers

Thus, recognition of the characteristic internal stress buildup in a plasma polymer is important for estimating the upper limit of thickness of a plasma polymer for a practical application. Poor results with respect to such parameters as adhesion and barrier characteristics are often due to the application of too thick a plasma polymer layer. The tighter the network of plasma polymer, the higher is the internal stress. Consequently, the tighter the structure, the thinner is the maximal thickness... 

The same plasma polymer deposited in a closed-system reactor has a graded elemental composition with a carbon-rich top surface, and the oligomer content is much lower [10], both of which increase the level of adhesion. The adhesion of the same water-borne primer is excellent and survives 8 h immersion in boiling water. When this surface is treated with O2 plasma, the adhesion does not survive 1 h of boiling, while the dry tape test still remains at the level of 5. The water-sensitivity of adhesion depends on the chemical nature of the top surface as depicted by XPS data shown in Figure 28.12. Water-insensitive tenacious adhesion, coupled with good transport barrier characteristics, provides excellent corrosion protection, as supported by experimental data [1-4], and constitutes the basic principle for the barrier-adhesion approach. 

It is clear from the study on pure iron that oxides participate in LCVD of TMS, and characteristics of plasma polymer films differ depending on the extent of oxides present on the surface when LCVD is applied. Oxides on the surface of pure iron are more stable than those on steel and hence more difficult to remove, but this can be effected by plasma pretreatment with (Ar + H2) mixture. SAIL by LCVD involving removal of oxides provides excellent corrosion protection of pure iron. The key factor of SAIL by LCVD for corrosion protection of metals in general is the handling of oxides, which depends on the characteristic nature of the metal oxide to be handled. Once strong chemical bonds were formed between nanofilm of plasma polymer, either through oxides or direct bonding to the substrate metal, the LCVD film acts as the barrier to corrosive species. 

The retardation of the migration of silicone oligomers from the silicone tubing after being coated indicates that the plasma polymer coating applied to the tube substrate is in a form of continuous film with barrier characteristics instead of some other physical forms (e.g., powder). Direct evidence of this aspect can also be seen from the fact that all test specimens prepared had passed the dye penetration test. 

The barrier characteristic of a thin layer is proportional to the value of (thickness)/(permeability) or (thickness) (transport resistance). Type B plasma polymers have a higher thickness limit but permeability is high. Although a thicker layer could be deposited... 

The pharmacokinetic performance of a drug influences the construction of a formulation. This has nowadays led to a dominance of drug delivery systems that provide a controlled or modified release of the drugs, defined as extended or delayed release. Release-controlling polymers are used to build up a barrier that prevents immediate release of a compound. In this way high peak plasma concentrations of drugs are avoided and usually only one dose per day is necessary. The characteristic properties of the formula are evaluated in in vivo tests where blood samples are analyzed often by extremely sensitive bioanalytical methods. 

Nanomodification creates improved fibre characteristics, e.g. mechanical strength, thermal stability, the enhancement of barrier properties, fire resistance, ion exchange capability, etc., for use in different application fields. In order to follow modification efficiency, various characterization techniques can be used, e.g. X-ray analysis to study composite structure, morphological observations by electron microscopy, mechanical tests, determination of electrokinehc properties, calorimetric measurements. The dispersion of particles within the hybrid system is of fundamental importance, and thus to observe particles a method based on selective etching of the polymer using a plasma... 

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