Plasma Treatment of Surfaces

In a final section the effects of plasma-treatment of surfaces and materials including catalysts are described. 

The principal problems for sdicone mbber as a viable lens material are the nonpolar nature, which gives Hpid deposits and wettabdity problems and the tendency to adhere to the cornea. Efforts to modify the sdicone lens surface for improved wettabdity have achieved limited success. These efforts include grafting hydrophilic monomers, such as HEMA, GM (150), and NVP (151—153), to the lens surface and plasma treatments of finished lenses. Efforts to improve the movement of sdicone lenses on the cornea with various lens designs have not been successfld, and the cause of lens—cornea adherence, which is not an exclusive problem of sdicone lenses, is an active area of research. 

The parameters of treatment were chosen since these led to the most pronounced changes of polymer surface in our previous experiments [70-74]. It was observed elsewhere that plasma treatment of polymer macromolecules results in their cleavage, ablation, alterations of chemical structure and thus affects surface properties e g. solubility [75]. The chemical structure of modified polyethylene (PE) was characterized by FTIR and XPS spectroscopy. Exposition to discharge leads to cleavage of polymeric chains and C-H bonds followed by generation of free radicals which easily oxidize [10,76]. By FTIR spectroscopy the presence of new oxidized structures within whole specimen volume can be detected. IR spectra in the 1710-1745 cm" interval [71,77] from PE, exposed to... 

Above described results prove that plasma treatment of PE leads to cleveage of molecular chain and production of polar groups. Since these changes may enhance interaction with polar solvents, the water etching of modified PE was examined the calculated thickness of the surface layer removed from plasma-modified PE (240 s, 8.3 W) by 24 hour water etching is 20.6 4.6 nm [78]. 

Jang, B.J., Das, H., Hwang, L.R., Chang, T.C. (1988). Plasma treatments of fiber surfaces for improved composite performance. In Proc. ICCI-II, Interfaces in Polymer. Ceramic and Metal Matrix Composites (H. Ishida ed.), Elsevier Sci. Pub. New York, pp. 319-333. 

C. Baquey, F. Palumbo, M.C. Porte-Durrieu, G. Legeay, A. Tressaud, R. d Agostino, Plasma-treatment of expanded PTFE offers a way to a biofunctionalization of its surface, NIM Nucl. Instmm. Methods Phys. Res. B 151 (1999) 255-262. 

Plasma treatment of powder substrates is difficult compared to that of a flat substrate. The main reason for this is the agglomeration of powders and the large surface area per unit mass of the powder. In order to modify the surface, each powder particle must be exposed to plasma. Unexposed regions are seldom modified. Therefore, the surface modification of powder substrates by plasma has to be dealt with differently. 

Fig. 7 Atomic force microscopy image illustrating defect structures in wrinkled surfaces prepared by plasma treatment of stretched PDMS and subsequent relaxation...

Bilayered polysilane LEDs have been obtained by inserting a SiOx thin layer between the cathode and a Wurtz synthesized PMPS emitter film.94 The SiOx layers were prepared by 02 plasma treatment of the PMPS film surfaces. It was found that the external quantum efficiency was significantly enhanced by this treatment. This enhancement has been attributed to an increased electron injection via tunneling, resulting in a reduced hole current caused by the blocking effect of the thin SiOx layer. The weak visible emission observed from single-layer polysilane LEDs is almost completely eliminated. It was concluded that the visible emission is caused by the erosion of the PMPS surfaces due to the collision with hot metal particles during the vacuum deposition of the cathode, and this erosion process is avoided by the SiOx layer. 

New catalysts of hydrogen oxidation for low-temperature fuel cells are molybdenum and tungsten carbides [2, 3], For solid polymeric fuel cells the novel catalysts by plasma treatment of polymer membrane have been developed. The radicals at surface are generated. These radicals are catalysts of anodic reactions [4]... 

The surface wettability by water drops has been clearly linked with the concentration of chemically bound nitrogen in the surface. Conversely, measurements of advancing and receding contact angles for water can provide information regarding surface composition. On the other hand, there appears to be little or no direct correlation between water wettability and adhesive strength of evaporated aluminum films. Substantial improvement in adhesion of Ai to many polymers can be achieved by 02 plasma treatment of the polymer surface before metallization. Other workers have shown this to result in chemical linkages between the metal and polymer surface moieties. 

Plasma treatments using various gases can introduce different functional groups to wood surfaces. They may also be used to improve the adhesive properties of plastic coatings. For example, plasma treatments are used industrially as a method of coating automobile bumpers. However, there are some problems in applying plasma treatments to wood. First, the equipment required for plasma treatments is expensive. Second, it is difficult to treat porous woods with plasma under reduced pressures. The latter problem has led to the investigation of normal pressure plasma treatments of wood. 

Polymer substrates are often coated with metals for a wide variety of reasons. In many cases, the chemical condition of the surface has been found Q) to alter the adhesion of the metal film to the substrate. In particular, oxygen plasma treatment of polymer surfaces before metal deposition has been found (, 4)... 

Figure 10.8 Scanned image of the surface of two alloy panels showing adhesion failure caused by the omission of O2 plasma treatment of the substrate prior to plasma film deposition and application of the primer (Deft 44-GN-72 MIL-P-85582 Type I Waterbased Chromated Control Primer), a) Panel after Skydrol LD4 fluid resistance test, which had the O2 plasma treatment prior to film deposition and primer application, b) Panel after scribed wet (24-h immersion in tap water) tape test, which had not been treated with the O2 plasma treatment prior to film deposition and primer application.

The main purpose of developing the AMT system is to treat large substrate surfaces via a scanning process. In order to investigate the effectiveness of AMT plasma treatment of large substrate surfaces, large CRS panels of 17.8 cm x 17.8 cm and 25.4 cm X 25.4 cm were used as the substrate. The experimental results are shown in Figures 17.35 and 17.36. 

The same principle applies to plasma surface modification. It is generally observed that O2 plasma treatment of a polymer surface dramatically increases the adhesion of paint applied on the treated surface. Flowever, the adhesion thus created... 

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