Thermally induced microstructural changes in undoped and doped polyacrylonitrile: A positron-annihilation study

Abstract

Positron-lifetime measurements have been made in undoped and polymers 0.8 wt%iodine-doped polyacrylonitrile (PAN) under annealing from room temperature to 160'C. From the measured lifetimes, the free-volume size is calculated following the treatment of Nakanishi, Jean, and collaborators. The variation in free-volume size as function of temperature seems to suggest molecular-chain-folding processes in amorphous regions of the polymer, positron trapping at kink-type defects, and at the interface between crystalline and amorphous regions at lower temperatures. This study indicates that in the undoped state, the polymer has a glass transition temperature at 90'C which is shifted toward lower temperature in the doped state by 30'C. The results also suggest the degradation of the polymer in the two states after 100'C and the effect of annealing is only on the size but not on the density of free-volume sites.

Temperature dependence of positron-annihilation lifetime, free volume, conductivity, ionic mobility, and number of charge carriers in a polymer electrolyte polyethylene oxide complexed withNH4<

“…11 The observed temperature dependence of the electrical conductivity of ion-conducting polymers has also been explained 1 in terms of the free-volume theory. The study of thermally induced microstructural changes leading to free-volume changes in polyacrylonitrile 12 ͑PAN͒ or free-volume change associated with the amorphicity of polymer salt complexes, 13 have been reported using a positron annihilation technique. In spite of all these studies the theoretical explanation of the measured ion transport properties is far from satisfactory.…”

Order‐disorder transitions in self‐assembled polymers: A positron annihilation study

“…180 Å 3 up to 55 o C and shows a stepwise decrease thereafter. It is known in polymers that the free volume gets reduced upon degradation [8]. A separate thermo gravimetric analysis (TGA) measurement do not show significant weight loss at this temperature thus revealing that the free volume reduction is not due to thermally induced degradation.…”

Ftir Study for Structural Pattern Changes Due to Irradiation in Pe-Pp Block Copolymer

“…Many modern machines and electronic components have polymers as one of the ingredient. Employing polymers in designing machines and electronic components has resulted in lowering the weight of those items and also the cost of their production [2]. But it is better to take care while using such machines and electronic components made of polymers in presence of radiations.…”