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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.

ABSTRACT We have investigated the effect of ion implantation on structural modification and the electrical conductivity of Bakelite-resistive plate chamber (RPC) detector material used in high energy physics experiments. Samples of Bakelite polymer were exposed to 100 keV and 150 keV oxygen ions in the fluence of 1012 to 1015 ions cm−2. Ion implantation induced microstructural changes have been studied using positron annihilation lifetime spectroscopy, X-ray diffraction and Fourier transform infrared techniques. Positron lifetime parameters viz., o-Ps lifetime and its intensity showed formation of radicals, secondary ions due to the creation of interior tracks by high-energy ions followed by chain scission at lower fluence of 100 keV implantation. The decreased free volume size at 150 keV ion implantation is an indication of crosslinking and filling up of interior tracks by the implanted ions. Variation of ac conductivity with frequency obeys Jonscher power law at 100 keV and the conduction mechanism is explained by barrier hopping model. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44962. [ABSTRACT FROM AUTHOR]

It is well established that copper sulfide is formed due to reaction of sulfur with copper conductors in transformers and reactors. However, there is very little experimental evidence to demonstrate copper sulfide diffusion into bulk of paper. Diffusion experiments have been carried out on three samples of kraft paper having different thickness. Positron Annihilation Lifetime Spectroscopy has been used to investigate the possibilities of copper sulfide diffusion into bulk of paper. This study has demonstrated that copper sulfide can diffuse into the bulk of paper leading to either increase or decrease in free volume of paper. The reasons for changes in free volume of paper due to copper sulfide deposits are explained. The consequences of copper sulfide diffusion on PD, voltage-current characteristics under ac and volume resistivity are discussed. Electric field simulation has been used to explain the effects of Cu ions and copper sulfide formation on electric stress distribution across paper. [ABSTRACT FROM AUTHOR]

To explore the structural modifications in terms of crosslink density and electrical conductivity in polymer based Bakelite RPC detector material was exposed to 8 MeV electron beam with the irradiation doses of 20 kGy to 100 kGy in steps of 20 kGy. The microstructural changes of Bakelite upon electron beam irradiation have been studied using Positron Annihilation Lifetime Spectroscopy (PALS), X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) Spectroscopy. Positron lifetime parameters viz., o-Ps lifetime and its intensity showed chain scission at lower doses (at 20 kGy and 40 kGy) followed by crosslinking due to the radical reactions. These changes are effectively explained with the help of FTIR and XRD parameters. The reduction in electrical conductivity of Bakelite material beyond 60 kGy is correlated between conducting pathways and crosslinks in the polymer matrix. The appropriate dose of electron beam on Bakelite might reduce the leakage current of Bakelite RPC detector material and hence improves the performance of the detector. [ABSTRACT FROM PUBLISHER]

Abstract: Positron lifetime spectroscopy is used to develop a new approach to characterize the individual interfaces in ternary polymer blends and hence determine composition dependent miscibility level. This approach has its genesis in KSR and KRZ models for the evaluation of hydrodynamic interaction parameters (αij). The method successfully applied for binary blends (single interface) earlier is theoretically modified for ternary blends and experimentally verified by measuring free volume content in blends and their constituents. We have tested the efficacy of this method in two ternary blends namely SAN/PVC/PMMA and SAN/EVA/PVC at different compositions. The effective hydrodynamic parameter αeff evaluated using individual α values turns out to be handy in predicting the overall miscibility level of a ternary blend. Results show that SAN/PVC/PMMA exhibits maximum αeff of −9.67 at composition 75/5/20 and SAN/EVA/PVC shows −3.18 at 50/35/15 indicating that miscibility level is high at these compositions for these two blends. DSC and SEM studies have also been used to supplement positron results. [Copyright &y& Elsevier]

The key requirements for a membrane in polymer electrolyte membrane fuel cells are a high ion conductivity, mechanical strength, and barrier properties. We reported earlier on two new promising hyperbranched polymers: poly(benzimidazole- co-aniline) (PBIANI), with a uniform rectangular net structure, and poly(benzimidazole- co-benzene) (PBIB), with a honeycomb structure. Both polymers exhibit a high ion conductivity and mechanical strength and have proven themselves suitable for the membranes of high-temperature polymer electrolyte membrane fuel cells. In this article, we deal with the determination of crystal structure and free-volume cell/microvoid size of these two polymers. Both PBIANI and PBIB had the same d-spacing (3.5 Å). However, the percentage of crystallinity was higher and the crystallite size was larger for PBIB. The kinetic diameters of hydrogen (2.89 Å), oxygen (3.46 Å), water (2.60 Å), and methanol (∼ 4.00 Å) were much larger than the free-volume cell/microvoid diameters of PBIANI (1.81 Å) and PBIB (1.96 Å) but much smaller than those of Nafion 115 (6.54 Å) and polybenzimidazole (PBI) (∼ 6.00 Å). The very small free-volume sizes of PBIANI and PBIB ensured good barrier properties against hydrogen, oxygen, water, and methanol, unlike those of Nafion- and PBI-type membranes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 [ABSTRACT FROM AUTHOR]

The article examines the probability of miscibility in binary polymer blends through hydrodynamic interaction. Free volume content in blends of carefully selected systems was measured via positron annihilation lifetime spectroscopy. A generalized model was utilized to understand the viscometric behavior of polymer/solvent systems to polymer/polymer systems in this free volume approach.

This study reports characterization of polyurethane/polymethyl methacrylate (PU/PMMA, 50/50) Semi-Interpenetrating Polymer Network (SIPN) prepared by in-situ polymerization, and filled with different weight percent (wt%) of natural polymer, Gaur-Gum (GG). These are characterized for density, tensile strength and percentage elongation at break. Positron annihilation lifetime measurements have also been carried out to measure the free volume of these composites. The results show good correlation between free volume content of the composites with the mechanical properties. These natural polymer-filled composites were subjected to biodegradation using a specific microorganism, Aspergillus niger. The influence of A. niger on composites has also been studied. The results show that the weight loss of the specimens exposed to A. niger media increases with increase in gaur gum in the composite. Interestingly the weight loss of GG-filled composites seems to be more than the quantum of GG incorporated which is a clear indication that degradation of PU/PMMA system is responsible for the weight loss. [ABSTRACT FROM AUTHOR]

The article presents the results of a study involving the effects of microwave and electron beam (e-beam) irradiation on immiscible and partially miscible polymer blends. Polymers studied included polyvinyl chloride, polymethylmethacrylate and ethylene vinyl acetate. The irradiation was used to modify the interfacial tension of the blends. Free volume data using the positron lifetime technique was analyzed, and a hydrodynamic interaction parameter was deduced from it. Microwaves were found to be more effective than e-beams for improving interfacial stability.

A comparative study of water and glucose sorption in a rigid gas-permeable contact lens polymer, Fluoroperm 92, has been carried out using positron annihilation lifetime spectroscopy, gravimetric analysis and refractive index measurements. The water sorption in FP92 is non-Fickian, whereas for glucose sorption it changes to Fickian. Glucose molecules reduce the interaction of water molecules with the polymer, resulting in more free water than bound water. It is observed that lenses which contain more bulk-water are prone to lens dehydration and corneal desiccation. The present results indicate that, in case of diabetics, as the glucose level increases in the aqueous humor, there would be more free water than bound water, which increases the propensity for corneal desiccation. The change in refractive index with increase in glucose content indicates decrease in optical transparency of the material. [ABSTRACT FROM AUTHOR]

The article discusses the free volume microprobe studies on polymethyl methacrylate/polyvinyl chloride and polystyrene blends. The blends were qualified using Differential Scanning Calorimetry which were found to be poor to describe whether polymethyl methacrylate/polyvinyl chloride blends are mixable due to the small gap in their glass temperatures. The blending may result to either compatible system or incompatible system.

The kinetics of moisture uptake in a rigid gas-permeable contact lens material, Fluoroperm60, has been investigated. The free volume changes accompanied by the sorption of water were monitored using the positron lifetime spectroscopy (PLS) technique. The positron results indicated swelling in the initial stages of sorption and the filling of vacant free volume sites with water in the later stages of sorption. The sorption curve suggests that the diffusion process in this polymer follows the dual-mode sorption model. Using this model, it was possible to separate Fickian-controlled diffusion and relaxation-controlled diffusion. Furthermore, the positron results combined with the sorption results indicated that Fujita's free volume theory does not seem to be valid for the diffusion process in the present sample under study. The variation of the permeability as a function of the free volume suggests that the amount of water in a contact lens is a measure of its permeability. [ABSTRACT FROM AUTHOR]

Abstract: A series of different weight ratios of guar gum viz. 5, 10, 20 and 30 were incorporated into polyurethane/polyacrylonitrile (PU/PAN, 50/50) semi interpenetrating polymer networks (SIPNs) using polyethylene glycol-400, 4,4′-diphenyl methane diisocyanate, acrylonitrile, benzoyl peroxide and new metallic catalyst. The obtained polymer composites were subjected to biodegradation studies using specific fungi Aspergillus niger. The composites are characterized for physico-mechanical properties like density and tensile behaviour of the specimens before and after biodegradation. The positron annihilation lifetime spectroscopy (PALS) was used to monitor the content of free volume before and after biodegradation. The extent of degradation was examined by change in tensile behaviour and surface morphology. The influences of fungi on mechanical and morphological behaviour of filled IPNs are found to be interesting. The free volume changes in the composite systems correlates well with the mechanical properties. [Copyright &y& Elsevier]

The morphology of immiscible and highly incompatible blends of Sorona® polymer [Poly(trimethylene terephthalate), PTT] and ethylene propylene diene rubber (EPDM) blends has been studied with and without the addition of a compatibilizer precursor EPM-g-MA. These incompatible blends are characterized by a two-phase morphology, narrow interphase, and poor physical and chemical interactions across the phase boundaries. Therefore, a reactive route was employed to compatibilize these blends by the addition of maleic anhydride grafted ethylene propylene rubber (EPM-g-MA). The blends were prepared in an internal mixer. The morphology was examined by scanning electron microscopy (SEM) after preferential extraction of the minor phase. The SEM micrographs were quantitatively analyzed for domain size measurements. The morphology of the blends indicated that the EPDM phase was preferentially dispersed as domains in the continuous Sorona® matrix up to 30% of its concentration. A co-continuous morphology was observed above 30 wt% of EPDM content followed by a phase inversion beyond 60 wt% of EPDM. The influence of EPM-g-MA on the phase morphology of blends was studied quantitatively by SEM. It was found that the addition of EPM-g-MA reduces the domain size of the dispersed phase followed by a leveling off at higher concentrations of the compatibilizer. This is an indication of interfacial saturation. The experimental compatibilization results were compared with theoretical predictions. The conformation of the compatibilizer at the interface was analyzed based on the area occupied by the compatibilizer at the blend interface. Free volume measurements using positron annihilation lifetime spectroscopy (PALS) were done to analyze the interaction of blends. In the case of uncompatibilized blends the free volume values tend to increase by the addition of EPDM phase showing high level of incompatibility. Addition of EPM-g-MA to the blends tends to decrease the free volume showing its compatibilizing effect. [Copyright &y& Elsevier]