Free radicals, in plasma

FREE RADICALS IN PLASMA POLYMER AND FREE RADICALS IN SUBSTRATE... 

Ungemach, F.R. (1985). Plasma membrane damage of hepato-cytes following lipid peroxidation involvement of phospholipase A2. In Free Radicals in Liver Injury (eds. G. Poli, K.H. Cheeseman, M.U. Dianzani and T.F. Slater) pp. 127-134. IRL Press, Oxford. 

The possible involvement of free radicals in the development of hypertension has been suspected for a long time. In 1988, Salonen et al. [73] demonstrated the marked elevation of blood pressure for persons with the lowest levels of plasma ascorbic acid and serum selenium concentrations. In subsequent studies these authors confirmed their first observations and showed that the supplementation with antioxidant combination of ascorbic acid, selenium, vitamin E, and carotene resulted in a significant decrease in diastonic blood pressure [74] and enhanced the resistance of atherogenic lipoproteins in human plasma to oxidative stress [75]. Kristal et al. [76] demonstrated that hypertention is accompanied by priming of PMNs although the enhancement of superoxide release was not correlated with the levels of blood pressure. Russo et al. [77] showed that essential hypertension patients are characterized by higher MDA levels and decreased SOD activities. 

Terao, J., Murota, K., and Moon, J.-H., Quercetin glucosides as dietary antioxidants in blood plasma modulation of their function by metabolic conbversion, in Free Radicals in Chemistry, Biology and Medicine, Yoshikawa, T., Toyokuni, Y., Yamamoto, Y., and Naito, Y., Eds., OIAC International, London, 2000, p. 50. 

TMS deposition on PE showed only substrate signals with no detectable TMS signal (Fig. 6.12b). The absence of the TMS signal in this system could be due to the fast reaction of TMS radicals with the surface radicals generated from PE. The more likely explanation is that the number of free radicals in the plasma polymer layer is too small in comparison with the free radicals created in the bulk of the substrate, PE. What we see in Figure 6.13 is the decay of PE polymer free radicals, which were created by the luminous gas of TMS. With substantial decay of the PE free radicals, TMS dangling bonds, which decay much slower, became discernible. 

All of the postdeposition treatments, even treatment with the more inert gas plasmas, leave the surface of the films in a silica-like state. This is thought to be due to the creation of free radicals in the luminous gas phase, which are quickly oxidized upon exposure to the atmosphere prior to analysis. 

It is tempting to use such relatively simple wet chemical methods to determine the amount of free radical on plasma polymers and on polymers treated with glow discharge. However, these methods have serious limitations when applied to the dangling bonds in plasma polymers or polymer free radicals in polymers treated with glow discharge. The most serious limitation is the accessibility of the chemical to the free radicals to be analyzed. Another serious limitation is the specificity of chemical reactions. 

The effect of pulsed discharge on plasma polymerization may be viewed as the analogue of the rotating sector in photoinitiated polymerization. The ratio r of off time 2 to on time ti, r = l2lti, is expected to influence the polymerization rate depending on the relative time scale of t2 to the lifetime of free radicals in free radical addition polymerization of a monomer. This technique was used to estimate the average lifetime of free radicals in the polymerization. 

In both the polymerizations, free radicals are the species that are responsible for the formation of bonds in the depositing materials. The growth mechanism, however, is not by the conventional chain-growth free-radical polymerization. In a conventional free-radical chain-growth polymerization, two free radicals and 10,000 monomer molecules yield a polymer with degree of polymerization 10,000, which does not contain free radicals. In contrast to this situation, in plasma polymerization and Parylene polymerization, 10,000 species with free radical(s) recombine to yield a polymer matrix that has an equivalent degree of polymerization, and contains numbers of unreacted free radicals (dangling bonds). 

Plasma coating or treatment in one stage followed by exposure to vinyl monomers for additional free radical initiated plasma polymerization. 

Resistance of polymers to ozone attack is studied in space environments in actual applications. In the laboratory, glow discharge or plasma etching is the common method for laboratory study of ozone effect. Plasma and low earth-orbit environments are not equivalent. For instance, oxygen plasma contains a variety of other particles including electrons and free radicals in addition to atomic oxygen. In contrast, atomic oxygen is the dominant constituent of low earth-orbit. 

In the bottom part of Table I, the reactions of free radicals in reactive plasmas are summarized. As described in the preceding sections, there are various reactive or transient species in reactive plasmas. It is generally accepted, however, that free... 

To clarify the roles of free radicals in reactive plasmas, it is necessary to measure the products in free radical reactions 1 though 5, which have not been fully understood in the physicochemical studies. 

The most specific property of plasma-polymerized films is a high concentration of free radicals in the films and a large niunber of cross-links between macromolecules. The... 

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