Some Principles of the Studies of Positron Annihilation in Polymer Systems

Abstract

Positron annihilation characteristics are used to find out the number and size of defects (elementary free volume) in some polymers considered as nonhomogeneous systems. The results obtained enable to understand some physico‐chemical proporties of these materials.

Positron annihilation study of iodine sorption in acrylonitrile-butadiene-styrene

“…ferent approaches. We follow the prescription outThe results from an XRD study shows this polylined by Goldanskii et al, 26 according to which mer to be semicrystalline with 52% crystallinity.…”

Thermally induced microstructural changes in cotton fibers: A free‐volume study

“…There seems to some difference of opinion with regard to the assignment of the intermediate-lifetime component ( 2 ) with intensity I 2. I followed the prescription of Goldanski et al, 18 according to which, this component is thought to arise due to the trapping of positrons in the defects present in the crystalline regions or in the crystalline-amorphous interface regions. The longest lived component ( 3 ) with intensity I 3 was attributed to pick-off annihilation of the o-Ps in the free-volume sites present in the amorphous regions of the polymer matrix.…”

“…Figure 3(a,b) shows the variation of 2 and I 2 as a function of annealing temperature. These changes corresponded to the crystalline regions as per the treatment of Goldanski et al 18 The molecular chains in cotton fibers take ordered arrangement and somewhat stable in the presence of water. 8 Because water molecules are present in the amorphous regions, as the removal of water molecule starts, the strain on the crystalline regions will be withdrawn, 28 and the chains get some freedom to rearrange.…”

“…11 I calcu- lated crystallinity as I 2 /(I 2 ϩ I 3 ) 18 and plotted it as a function of annealing temperature; this graph looked exactly like that of F v change (Fig. 4), suggesting that the crystallinity of cotton fibers increased with temperature, thereby reducing the F v in the final stages of annealing.…”

Degradation of acrylonitrile-butadiene-styrene and polycarbonate by UV irradiation

“…The shortest lifetime component ( 1 with intensity I 1 , is attributed to free annihilation of the positrons with a contribution from the decay of p-Ps. The second lifetime component ( 2 with intensity I 2 is considered to be due to the annihilation of positrons trapped at the defects present in the crystalline regions or trapped at the crystalline-amorphous interfaces [31]. The longest lifetime component ( 3 with intensity I 3 is attributed to the pick-o annihilation of the o-Ps in the free volume sites present mainly in the amorphous regions of the polymer matrix [30].…”