Positron annihilation mechanism correlated with microstructure of C-60-contained chitosan

Positron annihilation lifetime spectra measurements were performed on C-60- containing chitosan as a function of temperature ranging from 290 to 380 K. Both the ortho-positronium annihilation lifetime tau(3) and its intensity I-3 increase with increasing temperature, however, the values of I-3 in C-6 0-containing chitosan are smaller than that in pure chitosan, and the slope of tau(3) With temperature is also suppressed after C-60 linked. The exist ing three models for positron annihilation in polymer have been compared to analyse 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 phy sicochemical environment of material, i.e., free-volume structure, electron scavenging and trapping sites, etc. The linked C-60 that play a significan t chemical inhibition and quenching role on positronium formation and annih ilation is first observed. The microstructure change brought by C-60 group has also been discussed.