Plasma surface functionalization

It should be remarked that the plasma surface functionalization by oxygen plasma with and without reduction to monotype OH functional groups yields a lower peel strength compared to the use of the monotype functional groups bearing adhesion-promoting plasmapolymer layers (cf. Fig. 11). 

Bromination. Bromination of polymer surface employing the bromoform plasma presents a highly selective method of controlled surface functionalization. Only traces of Br anions were detected as negligible side-products by means of XPS and, under adverse conditions, the deposition of polymer layers was observed as measured with a microbalance. The XPS measured introduction of Br at polymer surfaces for two types of plasma treatment is illustrated in Fig. 4. 

The plasma membranes of many types of eukaryotic cells also contain receptor proteins that bind specific signaling molecules (e.g., hormones, growth factors, neurotransmlt-ters), leading to various cellular responses. These proteins, which are critical for cell development and functioning, are described in several later chapters. Finally, peripheral cytosolic proteins that are recruited to the membrane surface function as enzymes. Intracellular signal transducers, and structural proteins for stabilizing the membrane. 

Polymer surfaces, exposed to blood and blood plasma, can function like the stationary phase in partition liquid chromatography, that is, the molecular blood elements (lipids, proteins) cannot only adsorb on, but may dissolve into the surface layer of the polymer. 

Surface functionalization of PP films in the O2 plasma was performed in the cw mode. PP films which were coated with plasma polymer layers of functional-group carrying monomers had been used without any additional plasma pretreatment. PTFE films were exposed first to H2 radio-frequency (RF) plasma (cw mode) for 1-1800 s at pressure p=6Pa and power P=300W, followed by the deposition of adhesion-promoting plasma polymer layers. 

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). 

For many industrial applications of plastics that are dependent on adhesive bonding, cold gas plasma surface treatment has rapidly become the preferred industrial process. Plasma surface treatment, which is conducted in a vacuum environment, affords an opportunity to minimize or eliminate the barriers to adhesion through three distinct effects (1) removal of surface contaminants and weakly bound polymer layers, (2) enhancement of wettability through incorporation of functional or polar groups that facilitate spontaneous spreading of the adhesive or matrix resin, and (3) formation of functional groups on the surface that permit covalent bonding between the substrate and the adhesive or matrix resin. Since plasma treatment is a process of surface modification, the bulk properties of the material are retained. The nature of the process also allows precise control of the process parameters and ensures repeatability of the process in industrial applications. Finally, several studies have demonstrated that these surface modifications can be achieved with minimum impact on the environment. 

As effective as these surface modification processes might be, they present limitations in terms of the extent to which the surfaces of polymers can be modified. Plasma-induced grafting offers another method by which chemical functional groups can be incorporated. In this process, free radicals are generated on the surface of a polymer through the use of an inert gas plasma. Because of the nonreactive nature of the inert gas plasma, surface chemical modification of the polymer does not occur. If the polymer surface that has been... 

Y.L. Li, K.G. Neoh, and E.T. Kang, Plasma protein adsorption and thrombus formation on surface functionalized polypyrrole with and without electrical stimulation, J. Coll. Interf. Set, 275(2), 488 95 (2004). 

In the literature several methods to chemically modily poly(styrene) have been reported. The interest in the surface functionalization stems from the need to improve cell adhesion on PS petri-dishes for medical and biological applications, while PS cross-linking techniques were investigated for potential application as lithography resist. However, only two of the numerous reported techniques proved to be effective and suitable for the mesoporous styrenic templates, namely exposure to ozone or plasma ignited in several atmospheres, such as nitrogen, air, oxygen, and water vapor. 

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