Positron Annihilation Mechanism Correlated with Microstructure of C60-Contained Chitosan

Abstract

Positron annihilation lifetime spectra measurements were performed on C60-containing chitosan as a function of temperature ranging from 290 to 380 K. Both the ortho-positronium annihilation lifetime τ3 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 τ3 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.