Influence of polar groups in binary polymer blends on positronium formation

Abstract

The present work studied the role of the polar group unconjugated oxygen on the inhibition of positronium (Ps) formation in two binary blends made from a set of chosen constituent polymers with polar and weakly polar groups (nonpolar). The polymer blend samples of PVC-EVA and PVC-SAN were investigated by coincidence Doppler broadening and positron lifetime techniques. The strong polar acetate group in the EVA contributed to positron annihilation with electrons of unconjugated oxygen (-C + =O − ) as revealed by the momentum distribution curves peaking around 17 P L (10 −3 m 0 c). The ortho-Ps intensity indicated the unconjugated oxygen shows about a 28% Ps reduction even in the presence of a strong Ps inhibiting halogen (Cl − ). In contrast, this effect was not seen in the PVC-SAN blends since SAN contains a weakly polar (nonpolar) acrylonitrile group (C≡N). Our results indicate the chlorine of PVC in the blends is a major contributor to Ps inhibition through the formation of a (Cl − -e +) bound state but the unconjugated oxygen in EVA of the PVC-EVA blend also plays a similar, but lesser, role.

Positron annihilation and other experimental studies on polycarbonate/MPDMAPP nanocomposite

“…The measurements of Doppler broadening of the positron annihilation gamma ray line shape are helpful in monitoring the changes of the predominant trapping sites for positrons in doped polymer . The S‐parameter from DBS spectrum is defined as the ratio of counts in selected number of channels around the peak to the total number of counts under it and thus represents the fraction of positrons annihilating with low momentum electrons.…”

Structural and antibacterial properties of a γ‐radiation‐assisted, in situ prepared silver–polycarbonate matrix

“…Before annihilation, the neutral o ‐Ps particles were localized in regions of low electron density, such as free‐volume holes or cavities of the polymer. The probability of a pickoff process is related to the electron density near the cavity of the inner surface and, hence, to its size such that longer o ‐Ps lifetimes correspond to larger free‐volume holes …”

“…In polymers, ortho ‐positronium ( o ‐Ps; metastable bound state of electrons and positrons with parallel spin) preferentially localizes and annihilates in the free‐volume holes of a polymer . This characteristic of o ‐Ps makes it the microprobe of choice, and its lifetime and intensity become a measure of the electron density and free‐volume size in the study of the microstructural behavior of polymers …”

Blending ultrahigh‐molecular‐weight polyethylene and poly(ethylene/10‐undecen‐1‐ol) in one nascent particle

“…So far, these blends have always been synthesized by solution blending or melt blending . However, the miscibility of these two polymers is poor because of their unmatched molecular structures and the long relaxation time of the UHMWPE chains . The former will cause unmatched solubility parameters and also incompatible crystallization rates; this weakens interfacial adhesion .…”