Physical plasma treatment

Surface modification of a contact lens can be grouped into physical and chemical types of treatment. Physical treatments include plasma treatments with water vapor (siUcone lens) and oxygen (176) and plasma polymerization for which the material surface is exposed to the plasma in the presence of a reactive monomer (177). Surfaces are also altered with exposure to uv radiation (178) or bombardment with oxides of nitrogen (179). Ion implantation (qv) of RGP plastics (180) can greatiy increase the surface hardness and hence the scratch resistance without seriously affecting the transmission of light. 

Some physical techniques can be classified into flame treatments, corona treatments, cold plasma treatments, ultraviolet (UV) treatment, laser treatments, x-ray treatments, electron-beam treatments, ion-beam treatments, and metallization and sputtering, in which corona, plasma, and laser treatments are the most commonly used methods to modify silicone polymers. In the presence of oxygen, high-energy-photon treatment induces the formation of radical sites at surfaces these sites then react with atmospheric oxygen forming oxygenated functions. 

FIGURE 9.7 The contact angle of PDMS after various surface treatments (a) 3 h after 02 plasma treatment (28° C), (b) 48 h after 02 plasma treatment (70° C), (c) 144 h after 02 plasma treatment (90° C) and (d) parylene-coated PDMS (92° C)[1000]. Reprinted with permission from the Institute of Physics Publishing. 

Protein adsorption onto intrinsically repellent materials is enhanced by a brief plasma treatment that chemically and physically alters the surface properties. Stencil-assisted plasma oxidation of inherently hydrophobic polymers (e.g., PDMS... 

In this work, we have shown how a plasma treatment, which enables us to improve the Al-PP adhesion, leads to both chemical and physical modifications (the latter being observed for treatment time as short as 23 ms) at the polypropylene surface. 

Physical methods include plasma treatments, UV irradiation, corona discharge, and flame treatment. Among these, plasma treatment is widely used for the surface modification of synthetic polymers. Plasma can be obtained by exciting gases into an energetic state by radio frequency, microwave, or electrons from a hot filament discharge. Generation of plasma requires a vacuum, which normally poses several... 

The net effect of this treatment is that the virgin polystyrene is changed from a neutral, hydrophobic surface to a derivatized, charged hydrophihc surface that allows cell spreading and attachment (Dunn, 1984). The use of different gas mixtures in the controlled environment of the plasma treatment chamber can yield a variety of different surfaces (Figure 3.5.1). For a detailed discussion on physical analysis, see Salvati et al. (1991). 

This article describes some of the recent progress in the area of plaana polymerization and plasma treatment. It is not intended to be an exhaustive overview of the field, but instead a summary of the highlights of research studies in this field as perceived by the authors. Fundamentals of plasma physics and chemistry are also briefly described in order to hdp understanding of plasma processing in the gas phase and on the substrate. 

Many pretreatment techniques are used in practice (Table 8.2). The normal physical method used to improve the adhesive strength of the coating to the substrate is to slightly roughen the surface by solvent treatment, abrasion, or blasting. Some plastics (e.g., polyolefins) require special pretreatment methods processes that modify the surface molecular layers of the plastic to increase their polarity have proved suitable (e.g., flaming, immersion in an oxidizing acid, immersion in a benzophenone solution with UV irradiation, corona treatment, plasma treatment). 

To address these issues, several strategies for the preparation of such composites have been reported. Here we report some of these strategies involving physical mixing in solution, infiltration of monomers in the presence of nanotube sheets and chemical functionalization of CNTs by plasma treatment. 

Adhesion can be modified by chemical or physical methods to increase the surface free energy. The following procedures can be used for modifying the surface chemical treatment, ultraviolet treatment, flame treatment, and plasma treatment. 

Synthetic fibers do not contain natural impurities although there are added impurities such as sizing materials and oil stains. Therefore, their pretreatment process is simpler than other natural fibers. However, synthetic fibers such as polyester and acrylic have poor wettability, dyeability, and antistatic behavior. After plasma treatment, the fiber surface gets physically altered, and hydrophilic functional groups are introduced to the fiber surface, which improves the wettability of the fiber significantly. In recent years, many researchers have studied ways to modify polyester textile materials, and good results have been obtained (Morent et al., 2008). 

The capability of plasmas to modify the chemical and physical properties of the surface without affecting the bulk properties of the base material has been advcinta-geous in several cases [35-38]. Either surface modification or thin film deposition can create specific surface chemistries for optimization of membrane performances in separation processes [39]. It is well known that the surface wettabihty and the adhesion of polymer can be significantly improved by plasma treatment with non-polymer-forming gases. The plasma treatment also leads to the formation of radicals [35] that are promoters of surface cross-linking functionahzation. 

Nastuta, A.V., et al. Stimulation of wound healing by helium atmospheric pressure plasma treatment. Journal of Physics D Applied Physics 44(10), 105204 (2011)... 

Grigoras, C., et al. Influence of Atmospheric Pressme Plasma Treatment on Epithelial Regeneration Process. Romanian Journal of Physics 56, 54—61 (2011)... 

For surface modification applications, thick grafting layers are unnecessary and even undesirable because they may change bulk physical properties of the polymer, such as crystallinity and tensile modulus. A two-step method can be used to minimize the formation of the homopolymer. The polymer is preirradiated in air to produce peroxide groups on the surface. Grafting is subsequently initiated thermally in contact with a monomer. Other methods such as corona discharge, ozone treatment, and plasma treatment have also been used to generate peroxide groups on polymer surfaces. 

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