Correlation between Electron Density and Momentum in Free Volume Holes of Some Semicrystalline Polymers

Abstract

Positron annihilation lifetime (PAL) and Doppler broadening (DB) measurements were carried out in four semicrystalline polymer samples, viz., polycarbonate (PC), acrylonitrile-butadiene-styrene (ABS), polytetrafluoroethylene (PTFE), and Nylon 6, 6 (PA). A correlation between the S and Wparameters which reflect the electron momentum, and the orthc-positronium (0-Ps) lifetime reflecting the electron densities in free volume sites is observed. Interestingly, the present results support the known intuition that 0-Ps has a higher momentum component compared to p-Ps and free annihilations but different from that observed by Davies and Pethrick.') Manasagangotri, Mysore 570 006, India.1'

Free-volume microprobe study of iodine diffusion in polymers

“…Even though the Fujita's free‐volume theory satisfactorily describes the diffusion of a number of organic liquids and vapours in polymer solutions, there have been no attempts to correlate the diffusion coefficient with the fractional free‐volume by direct measurement of these two quantities, particularly in solid phase of the polymers. In recent times, positron lifetime spectroscopy (PLS) has been found to be an attractive and sophisticated tool for determining the angstrom‐sized free‐volume holes and their concentration in polymers 16–18. We use this technique in the present study to measure the free‐volume change upon iodine diffusion in the three polymers acrylonitrile–butadiene–styrene (ABS), poly(ethylene terephthalate) (PET) and polycarbonate (PC).…”

Diffusion of seawater in unsaturated polyester resin and its glass fiber reinforced composites in the presence of titanium dioxide as UV absorber

“…Thermoset polymers, because of their highly crosslinked structure, are expected to contain small size free volume cavities. 21,22 as compared to thermoplastics like polycarbonate, 23 polyethyleneterephthalate, 23 polytetrafluoroethylene, 24 etc. The curing of UPR involves free-radical chain growth crosslinking and hence is expected to be highly crosslinked owing to its covalently bonded structure.…”

Water Sorption Studies in a RGP Contact Lens Polymer Paraperm by Positron Lifetime Technique

“…The source-sample sandwich geometry (sample on either side of 22 Na positron source) was used for the positron lifetime measurements. More details of the experimental procedures are reported elsewhere [3,11]. Positron lifetime spectra with more than 10 6 counts under each spectrum were recorded for each sorption time.…”