Masayuki Kuzuya*, Kosuke Ito, Yukinori Yamauchi, Shin-ichi Kondo

Laboratory of Pharmaceutical Physical Chemistry, Gifu Pharmaceutical University
5-6-1, Mitahora-Higashi, Gifu 502-8585, Japan
kuzuya@gifu-pu.ac.jp

In view of the fact that surface reactions of plasma treatment are initiated by plasma-induced surface radicals, we have often emphasized that study of the radicals formed is of utmost importance for full understanding of the nature of plasma treatment. Thus, we reported a detailed electron spin resonance (ESR) study on plasma-induced radicals of a variety of synthetic and natural polymers.

In general, chemical reactions are controlled by intensive properties such as concentration, temperature, pressure and so forth, but plasma reactions are controlled by not only intensive properties but also extensive properties such as shape and size of plasma chamber and the method of plasma generation. Thus, experimental design including establishment of correlation between result of plasma treatment and plasma-operational conditions is a difficult and complicated task. If you fully understand, however, the nature of plasma-induced free radicals (generated radical quantity, structure and its reactivity etc.) formed on each polymer surface, you can discuss the experimental data of plasma treatment conducted under various plasma-operational conditions on comparable basis, since plasma-irradiation eventually affects the surface radical formation whatever plasma operational conditions may be.

We have carried out a number of argon-plasma irradiations on polycrystalline carbohydrates under various kinds of plasma operational conditions such as plasma duration, plasma power, and Ar pressure and, and the radicals formed was studied by ESR. Among carbohydrates studied, it was found that polycrystalline myo-inositol could be the best carbohydrate, since it gives several kinds of plasma-induced radicals some of which undergo thermal rearrangement resulting in the formation of different type of radicals, and then various types of ESR spectra were obtained depending on the plasma-operational conditions. Thus, the analyses of free radicals of plasma-irradiated myo-inositol can be used as spin probe for chemical plasma diagnosis. The present method is also very useful for future experimental designs of effective plasma treatment.