Plasma polymer coatings properties

Parylene N to smooth surface materials has been reported with the application of plasma depositions [13,14]. It was reported that excellent adhesion of Parylene C coating to a cold-rolled steel surface was achieved using plasma polymer coatings, in turn giving rise to corrosion protection of the metal [15]. Another major deficiency of Parylene C is its poor painting properties when paint is applied on a Parylene C film, due to its extremely hydrophobic surface. Because of this, surface modification of Parylene films is necessary to enhance their adhesion performance with spray primers. 

In contrast, a significant increase of the Rp values was observed with the application of a thin layer of TMS plasma polymers (about 50 nm) on these chemically treated [2A] surfaces. It was also noted that these TMS plasma polymer-coated [2A] samples have the same level of Rp values as the [2A]CC controls. These results clearly indicate that these plasma polymer coatings have a good corrosion resistance property. 

The separation properties of the membranes vary not only with the thickness of the plasma polymer coatings but also with the conditions of LCVD. One such plot of the variation is shown in Figure 34.21 [14]. The upper portion of this figure shows how the specific conversion parameter, DRjFM, varies as a function of the composite energy input parameter, WjFM. DR is the nominal deposition rate of plasma polymer film on the surface of a quartz crystal thickness monitor located in the plasma reactor, adjacent to the hollow fibers. 

Basarir, R, Choi, E.Y., Moon, S.H., Song, K.C. and Yoon, T.H. 2005. Electrochemical properties of PP membranes with plasma polymer coatings of acrylic acid. 

Glow discharge or "cold" plasmas are gaining increased currency for the deposition of novel and potentially valuable macromolecular coatings. The range of properties attainable by a plasma-polymer is wide, and depends critically on such variables of the plasma deposition process as choice of monomer, substrate temperature (T ), power density (p), the excitation frequency (v), and others incluSing monomer flow rate, reactor geometry, etc... Control over these variables can produce crossllnked, dense deposits which adhere tenaciously to... 

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. 

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... 

The expansive internal stress in a plasma polymer is a characteristic property that should be considered in general plasma polymers and is not found in most conventional polymers. It is important to recognize that the internal stress in a plasma polymer layer exists in as-deposited plasma polymer layer, i.e., the internal stress does not develop when the coated film is exposed to ambient conditions. Because of the vast differences in many characteristics (e.g., modulus and thermal expansion coefficient of two layers of materials), the coated composite materials behave like a bimetal. Of course, the extent of this behavior is largely dependent on the nature of the substrate, particularly its thickness and shape, and also on the thickness of the plasma polymer layer. This aspect may be a crucial factor in some applications of plasma polymers. It is anticipated that the same plasma coating applied on the concave surface has the lower threshold thickness than that applied on a convex surface, and its extent depends on the radius of curvature. 

The three key features of LCVD coating ideally suited for biomaterial surface, and the important balance between the bulk properties and the surface properties, could be best illustrated by examples of nanofilms of methane plasma polymer on a contact lens made of polydimethylsiloxane elastomer. Hence, some details of processing factors and their influence on the overall properties of the product are described in the following sections. 

A capacitively coupled reactor designed to permit continuous coating of a moving substrate with plasma polymer has been described [ 1 ]. In this paper the results of a study of the plasma polymerization of tetrafluoroethylene in such a reactor presented. Plasma polymer has been deposited on aluminum electrodes as well as on an aluminum foil substrate placed midway between electrodes. The study particularly explores conditions in which deposition is minimized on the electrode. For this reason the chemical nature of the polymer formed in a low flow rate (F = 2 cm (S.T.P.)/min) and low pressure (p = 60 mlllltorr) plasma has been analyzed by the use of ESCA (electron spectroscopy for chemical analysis) and deposition rate determinations. This method combined with the unusual characteristics of TFE plasma polymerization (described below) has yielded Information concerning the distribution of power in the inter-electrode gap. The effects of frequency (13.56 MHz, 10 KHz and 60 Hz), power and magnetic field have been elucidated. The properties of the TFE plasma polymer prepared in this apparatus are compared to those of the plasma polymer deposited in an inductively coupled apparatus [2,3]. 

Thin films with a broad spectrum of properties can be deposited in plasma chemical processes [30, 31]. Hard coatings such as diamond films and TiN films, soft plasma polymer films, insulating SiO films, highly conducting Si films, anti-reflection coatings, semi-permeable membranes and very effective diffusion barriers can be deposited. Important parameters for the film deposition are (i) the nature of the precursor, (ii) the gas mixture and... 

A direction in designing inhibited polymer coatings using new principles has been proposed in [47]. A layer of corrosion inhibitor (p-hexamethylene imine nitrobenzoate) applied onto a steel substrate is polymerized in a low-temperature plasma. The high protecting properties achieved by this coating... 

Young s modulus values of 2.7 GPa. Plasma-enhanced chemical vapour deposition (PECVD) was successfully used to produce a PMMA conformal coating (using methyl methacrylate monomers) on MWNTs. This increased the Young s modulus to 2.85 GPa at 3 wt% which corresponds to dT/dFf of 28.4 GPa. The overall set of mechanical properties indicates that the polymer coating had a significant effect on the mechanical properties at a 1 wt% concentration of tubes, suggesting improved interfacial adhesion between the filler and the matrix material. 

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