Plasma polymer surfaces

Figure 9 shows the pH dependence of electro-osmosis in l mM NaCl for three plasma polymer surfaces having different functional characteristics. The respective surfaces of Fig. 9 are plasma polymerized acrylic acid, hexamethyl-disiloxane (HMDSO), and l, 2-diaminocyclohexane (DACH). It is evident from the figure that these surfaces have very different electrokinetic surface properties. This surface titration clearly distinguishes the acid-base properties of the respective surfaces. 

FIG. 9 The pH dependence of electro-osmotic fluid flow for three plasma polymer surfaces in I mM NaCl acrylic acid (O), HMDSO ( ), and DACH (A). 

Lassen and Malmsten have performed ellipsometrically determined in situ protein adsorption measurements on the above plasma polymer surfaces with human serum albumin (HSA). human immunoglobulin (IgG), and human fib-... 

It is important to note that HFE is not a monomer of general plasma polymerization because it does not polymerize in the absence of hydrogen in a reactor system [22]. When it is applied to a TMS plasma polymer surface, however, hydrogen is abstracted from the surface and forms a very thin layer of plasma polymer. It is essentially a self-terminating deposition process leading to an extremely thin layer of HFE plasma polymer. XPS analysis indicated that the thickness of the F-containing layer in the TMS/HFE system is less than a few nanometers [23]. 

Plasma deposition on a hydrogen-containing surface from HFE is a selfterminating plasma polymerization process. When the initial plasma polymer surface, which contains hydrogen atoms, is sufficiently covered by the plasma polymer of HFE, the deposition ceases because the supply of hydrogen diminishes. 

Adhesion of the cathodic E-coat to the plasma polymer surfaces is an important parameter in the corrosion protection of A1 alloys. In general, the adhesion performance of E-coat applied to plasma polymers was found to be far superior to that of the control panels. A-Methylpyrrolidinone (NMP) paint delamination was not observed after 120 min for E-coat on plasma polymer surfaces as compared to a maximal time for complete delamination of 5 min for E-coat on chromate conversion coating [2B] CC/E panels. The adhesion performance of cathodic E-coat on the plasma polymer surfaces could not be differentiated by the conventional tape test (ASTM D3359-93B), since E-coat on all of the combinations... 

CHROMATED AND NONCHROMATED SPRAY PAINTS ON PLASMA POLYMER SURFACES... 

Figure 33.2 shows XPS spectra of the surfaces of the TMS plasma polymer film deposited on (Ar + H2) plasma-pretreated steel (a, b, c) and on O2 plasma-pretreated steel (d, e, f). As shown in the spectra, the surface of the plasma film is functional in nature with functional groups of C-OH, C=0, and Si-OH. Two films basically ended up with the same surface structure. This is also confirmed by XPS analysis of the film during the film aging in air after the film deposition, which indicated that the film surfaces were saturated with a fixed surface structure after a few hours of air exposure [4]. This is due to a well-known phenomenon that the residual free radicals of the plasma polymer surface reacted with oxygen after exposure to air [5]. Curve deconvolution of C Is peaks showed structures of C-Si, C-C, C-0, and C=0. The analysis clearly shows a silicon carbide type of structure, which is consistent with the IR results. The functional surfaces of TMS films provide bonding sites for the subsequent electrodeposition of primer (E-coat). 

Fig. 18.7 Al peel strength of Al-plasma copolymer-PP composites as a function of functional group density at the plasma polymer surface (squares COOH half-filled squares COOH circles OH triangles NHj copolymers ethylene and butadiene).

A control experiment entailed immersion of the cyclic imide functionalized plasma polymer surface into THF at 25 °C for 1 h. No changes in the infrared spectrum were observed (not shown). The intermediate amide functionalized plasma polymer surface was also exposed to a solution of cyclopentadiene in THF at 25 °C for 1 h. Infrared analysis showed spectral features similar to those described above for the imide surface, the main difference being the peak between 1800 and 1600 cm indicating the presence of amide rather than imide linkages at the surface. Finally, the plasma polymer surface functionalized with cyclic imide groups was exposed to [(trimethylsilyl)methyl]cyclopentadiene solution in cyclohexane at 25 °C for 1 h. Two new bands appeared at 2975 and 2890 cm characteristic of the asymmetric CH3 stretching and the symmetric CH3 stretching (Fig. 19.3, spectrum c). 

The quantitative elucidation of the surface confinement effect of dienophile groups on the Diels-Alder reaction led to the conclusion that the reaction at the pulsed plasma polymer surface is significantly different from the reaction in the monolayer. The plasma polymer thin films are less reactive than the monolayers but the transition-state complex is more ordered. This means that this transition-state complex is more stable at the pulsed plasma polymer surface than on monolayers because of the chemical environment of the molecules. Since the reaction at the plasma polymer is significantly more confined than in mono-layers, the reaction is less affected by the temperature. These first results need to be completed by XPS and FTIR spectroscopic analysis in order to obtain quantitative elucidation of the reactivity in the entire pulsed plasma polymer thin film. 

Steen, M.L., Butoi, C.I. and Fisher, E.R. 2001a. Identification of gas-phase reactive species and chemical mechanisms occurring at plasma-polymer surface interfaces,... 

One of the main conclusions of the WgL measurements is that only sulphur dioxide as reactive component causes an acidic surface. In all the other plasma polymer surfaces, basic groups are more dominant. 

Malmsten M, Muller D, Lassen B. Sequential adsorption of human serum albumin (HSA), immunoglobulin G (IgG) and fibrinogen (Fgn) at HMDSO plasma polymer surfaces. J Colloid Interface Sci 1997 193 88-95. 

The addition of water soluble corrosion inhibitors to coating systems can be problematic due to the solubilisation of the inhibitors causing osmotic blistering. One approach is to coat inhibitors with a plasma-polymer surface to reduce the release rate of the encapsulated inhibitor. Yang and van Ooij [131] coated triazole particles with an inner layer of (hydrophobic) perfluorohexane plasma polymer and then an outer layer of pyrrole plasma polymer. The resultant particles were then dispersed into a water-based epoxy and it was shown that the release rate of the triazole had been significantly reduced and blistering was not observed. 

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