Positron Annihilation Mechanism Correlated with Microstructure of C₆₀-Contained Chitosan

Positron annihilation lifetime spectra measurements were performed on C₆₀-containing chitosan as a function of temperature ranging from 290 to 380K. Both the ortho-positronium annihilation lifetime т₃ and its intensity I₃ increase with increasing temperature, however, the values of I₃ in C₆₀-containing chitosan are smaller than that in pure chitosan, and the slope of т₃ with temperature is also suppressed after C₆₀ linked. The existing three models for positron annihilation in polymer have been compared to analyze the experiment result. It is realized that only the spur reaction model, combined with the free volume model, can explain it satisfactorily. The ortho-positronium lifetime and intensity were affected by the local physicochemical environment of material, i.e., free-volume structure, electron scavenging and trapping sites, etc. The linked C₆₀ that play a significant chemical inhibition and quenching role on positronium formation and annihilation is first observed. The microstructure change brought by C₆₀ group has also been discussed.