Plasma polymer structure

Frequently plasma polymers are not classified in respect of the type of monomer but from a point of view of their chemical composition and morphology. For example, amorphous (a-) covalent material obtained by plasma polymerization of silane (SiFLj), which is composed of silicon and hydrogen, can be termed as a-Si H. In turn, amorphous plasma polymer deposited from acrylonitrile (C3H3N) can be called as plasma-polymerized (pp-) acrylonitrile or a-CxNy H. It is usually met, but it is not a rule, that if the plasma polymer structure is close to a covalent glass structure, the latter notation is used. If plasma polymer reveals nano- or microcrystalline structures, prefixes nc- or pc- are put in the place of a-. 

Levels and detection frequency of TBBPA are generally lower than those of PBDEs and HBCDs in human samples. Consistent with its phenolic structure that can be rapidly conjugated in human hver and subsequently excreted in bile [36], TBBPA has a short human half-life that has been reported to be as low as 2 days in human plasma [28, 37]. In addition, HBCD and PBDEs are additive BERs, while TBBPA is a reactive BFR, meaning that TBBPA is chemically bound to the polymer structure and, thus, the leaching or release of TBBPA into the environment is limited [38]. Therefore, levels of TBBPA are often lower and detection of this... 

Primary interest was in the barrier properties obtained from plasma organo-silicones and from inorganic "SIN" coatings. Spectral grade HMDSO was used in the former case, while mixtures of SiH and NH were used to produce the SIN structures. The substrate in much or the work was DuPont Kapton type H polylmide film, 51 pm thick. Substrate temperatures extended to 450 C, as described earlier (6). The thickness of plasma-polymer deposits was about 0.5 pm. Moisture permeation was evaluated by the routine of ASTME-96-53 T (water vapor transmission of materials in sheet form). Additional, more precise data, were obtained with both a Dohrmann Envirotech Polymer Permeation Analyser, modified as previously described (6), and a Mocon "Permatran W" moisture permeation apparatus. 

Functionalities on the sulfur surface - ToF-SIMS was applied to both the untreated sulfur and the plasma polymer-encapsulated sulfur to obtain structural information on the outermost layer of the samples. The positive and negative spectra of untreated sulfur are presented in Fig. 13. Compared to Fig. 13b, there are clearly more peaks in the positive spectra in Fig. 13a, which come from hydrocarbon ions in the low molecular weight range. It is interesting to see that sulfur forms almost identical characteristic peaks of Si, S2 up to Sn in both the positive and the negative spectra. 

A core-shell structure can be seen in Fig. 16, which shows a cross-section of about 100 nm of sulfur aggregate encapsulated with poly acetylene. The plasma polymer layer is rather coherent while in other cases loose structures are also observed. 

For the cyclic corrosion test, a layer of acrylosilane polymer coating (10-25 fim thick) was dip-coated onto the plasma-deposited substrates. The coated samples were then subjected to 25 scab cycles. The test results are plotted in Fig. 7. Corrosion performance (as described by the length of scribe creep) was correlated to the wattage used for plasma film deposition. As discussed in the previous section, the chemical structure and properties correlated with the deposition conditions, especially the power level applied. Therefore, atomic compositions for plasma polymers deposited at different power levels were also plotted in Fig. 7.A... 

It should be remembered that the aim of this work was to produce defined layers with monosort functional groups, which can be used for grafting. Now, in contrast to the irregularly structured continuous-wave plasma polymers, the structure of pulsed plasma polymers was so much improved that partial or complete solubility was observed. Therefore, the further chemical processing in solvents and water led to dissolving the layer. Here, also chemically crosslinking copolymers as butadiene, di-vinylbenzene and trivinylcyclohexane were necessary as schematically shown in Fig. 9. 

Regular, highly branched macromolecule with a monodisperse, tree-like or generational structure Trimethoxysilylpropyldiethylenetriamine Hydrophobic hexamethyldisloxame Hydrophobic hexamethyldisloxame plasma polymer Guanido biotin derivative... 

In recent papers we have shown how ESCA may be used to establish relationship between the structure of the initial molecular system in which the discharge is excited and that of the polymer deposited in either glow or non-glow reations (12). The objectives of the present progrannie of work on plasma polymers may be sunniarized as follows ... 

Figure 14. Apparatus for studying site dependence of structure of plasma polymers...

The similarity of the Cls spectra for the three films in Figure 11 suggests that the polymer structure is the same irrespective of the excitation electrode material used. It has been noted that the Cls spectra in Figure 11 are also similar to that of plasma polytetrafluoroethylene formed under similar conditions (9, 2 ). This observation, coupled with mass spectrometric... 

A thorough understanding and careful control of plasma parameters can enable the process to be tailored to the desired application. It must be acknowledged however, that in spite of an impressive number of studies reported, an accurate prediction of the molecular structure of plasma polymers is not available. However, attempts have been made to examine the effects of various deposition parameters on the growth of plasma derived polymer thin films, and some of the results are summarized below. 

For LCVD interface engineering of composite materials, it is considered that the tight three-dimensional network is necessary because of the required structural integrity, i.e., type A plasma polymers are essential for LCVD interface engineering. Low-pressure plasma polymerization is considered ideal for such applications because of the mechanisms of polymerization or material formation. 

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