A positron annihilation lifetime study of isothermal structural relaxation in bisphenol‐A polycarbonate

Abstract

SynopsisPositron annihilation lifetime spectroscopy has been used to study the isothermal relaxation response of compression molded bisphenol-A polycarbonate at temperatures of 263, 273, and 303 K. The temperature dependence of both the lifetime and intensity of the ortho-Positronium (0-Ps) pickoff component is discussed in terms of ductile-to-brittle transition behavior and free .volume theory. An additive exponential model and the Williams-Watt model were used to ;analyze the relaxation as a function of temperature and provided results consistent with the anticipated molecular mobility of polycarbonate at sub-2' ' temperatures.

Differential scanning calorimetric and free volume study of reactive compatibilization by EPM‐g‐MA of poly(trimethylene terephthalate)/EPDM blends

“…Hence, three‐component analysis results are presented here. The attribution of these lifetime components is as follows 12–21. The shortest lifetime component τ 1 (0.130–0.170 ns) with intensity I 1 (45–50%) is attributed to p‐Ps and free positron annihilations.…”

“…PALS is one of the sophisticated tools currently available for determining directly the nanometer‐sized free volume cavities and their relative number density (concentration) in polymers10–14 and recently, in polymer blends 10. To enunciate the versatility of this method, we mention only a few of the interesting studies carried out using this technique: water sorption in contact lens polymers,15 polymers containing silver nanoparticles,16 structural relaxation of polyethylene terephthalate and polycarbonate,17–19 ageing studies on polymers,20 etc. When positrons from a radioactive source ( 22 Na) are injected into a molecular medium like polymers or blends, they reach thermal energy in a very short time (∼1 ps), through the interaction with the surrounding atoms and molecules, losing the energy by inelastic collisions.…”

Compatibilizer‐induced microstructural changes in poly(trimethylene terephthalate)/EPDM blends studied by the positron annihilation lifetime technique and differential scanning calorimetry

“…PALS is one of the sophisticated tools currently available for determining directly the angstrom‐sized free volume holes and their relative number density (concentration) in polymers,10–14 and also recently in polymer blends 11. Interesting studies carried out using PALS have included water sorption in contact‐lens polymers,15 polymers containing silver nanoparticles,16 structural relaxation of PET and polycarbonate,17, 18 and ageing studies on polymers,19 which clearly show the versatility of the technique. When positrons from a radioactive source ( 22 Na) are injected into a molecular medium like polymers, they reach thermal energy in a very short time (around 1 ps), through interaction with the surrounding atoms and molecules and losing energy by inelastic collisions.…”

“…Ps can exist in one of two allowed spin states: para‐positronium (p‐Ps) if the spins are aligned antiparallel and which annihilates into two gamma rays with a lifetime of 125 ps, or ortho‐positronium (o‐Ps) if the spins are parallel and which annihilates into three gamma rays with a lifetime of 140 ns in free space. Owing to the fact that o‐Ps is preferentially localized in the free‐volume holes of polymer systems,10–20 the PALS parameters, namely o‐Ps lifetime (τ 3 ) and its intensity ( I 3 %), have been widely used in the study of microstructural behaviour of this class of materials. It is usual to correlate the relative concentration of the free‐volume holes to the viscoelastic properties of the system under investigation.…”

A study on free volume of acrylonitrile-styrene copolymer and methyl methacrylate-styrene copolymer by using positron annihilation

“…[1][2][3] According to a theoretical model of Tao and Eldrup, 4,5 the ortho-positronium (o-Ps) is assumed to reside in a spherical potential well, and it gives the connection between the o-Ps lifetime 3 and average radius of the potential well. Within this framework, the average size of free volume holes could be estimated by means of a semiempirical equation.…”