Journal ArticleDOI
Positronium annihilation in amine‐cured epoxy polymers
TLDR
In this article, the authors determined the free-volume hole sizes in amine-cured epoxy polymers by comparing the observed ortho-positronium lifetimes with the known lifetime-free volume correlation for low-molecular-weight systems.Abstract:
Positronium annihilation spectroscopy (PAS) has been used to study the microstructural properties of amine-cured epoxy polymers. We have determined the free-volume “hole” sizes in these polymers by comparing the observed ortho-positronium lifetimes with the known lifetime–free volume correlation for low-molecular-weight systems. The free volumes for four epoxies with different crosslink densities are found to vary significantly over the temperature range between −78° and 250°C. The free-volume holes for these polymers are found to range from 0.025 to 0.220 nm3. Two important transition temperatures were found: one corresponds to the glass transition temperature Tg determined by differential scanning calorimetry (DSC), and the other occurs about 80–130°C below Tg. The sub-Tg transition temperature is interpreted tentatively as being where hole size reaches dimensions adequate for positronium trapping or else the onset temperature for local mode or side-chain motions. These two transition temperatures plus two additional onset temperatures are found to be correlated with crosslink densities calculated from stoichiometry.read more
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Journal ArticleDOI
Positron annihilation spectroscopy for chemical analysis: A novel probe for microstructural analysis of polymers☆
TL;DR: Positron annihilation spectroscopy for chemical analysis (PASCA) has been developed to analyze the microstructure of polymers as discussed by the authors, where the positronium atom is trapped in the atomic-scale holes which have a size ranging from 1 to 10 A. Theoretical aspects, experimental developments, and examples in analyzing the microstructures of epoxy, PEEK, and PMMA polymers are presented.
Journal ArticleDOI
Positron annihilation : A probe for nanoscale voids and free volume ?
Journal ArticleDOI
Positron annihilation lifetime studies of changes in free volume on cross-linking cis-polyisoprene, high-vinyl polybutadiene, and their miscible blends
R. Srithawatpong,Z. L. Peng,B. G. Olson,Alex M. Jamieson,Robert Simha,John D. McGervey,T. R. Maier,Adel Farhan Halasa,Hatsuo Ishida +8 more
TL;DR: In this paper, the authors measured the fractional free volume hole sizes in vulcanized cis-polyisoprene (CPI), high-vinyl polybutadiene (HVBD), and their 50 : 50 blend were made via determination of orthopositronium annihilation lifetimes.
Journal ArticleDOI
Effect of cross-linking on the free-volume properties of diethylene glycol bis(allyl-carbonate)polymer networks: a positron annihilation lifetime study
Günter Dlubek,J Stejny,M A Alam +2 more
TL;DR: In this article, the effect of cross-linking on the free-volume properties of poly(diethylene glycol bis(allyl carbonate)) networks was studied using a series of networks with progressively decreasing density of crosslinks.
Journal ArticleDOI
Nanoscopic properties of silica filled polydimethylsiloxane by means of positron annihilation lifetime spectroscopy
TL;DR: Positron annihilation lifetime spectroscopy (PALS) was performed on a series of polydimethylsiloxane (PDMS)/fumed silicon dioxide (SiO2) composites at temperatures between -185 and 100degreesC to study the effect of filler content and filler particle size on the free volume properties and the positron annihilation characteristics as mentioned in this paper.