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Abstract: Interfaces in binary polymer blends play a pivotal role in moulding their physical properties. We observe a diffused interface in immiscible and partially miscible binary polymer blends for which the methods of preparation characterize the interface widths. The interface widths for three binary blends of PVC/PS, PS/PMMA, and PVC/SAN are in the maximum range of 2.15, 5.04 and 6.24 nm respectively. We establish a correlation between hydrodynamic interaction and the Flory–Huggins interaction parameter which is consistent with self-consistent mean field theory and the usual constructed density profile across the interface. Our approach is based on the hydrodynamic interaction which is derived from free volume data measured by positron lifetime spectroscopy. [Copyright &y& Elsevier]

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]

Erosion characteristics of high chromium (Cr, 16-19%) alloy cast iron with 5% and 10% manganese (Mn) prepared in metal and sand moulds through induction melting are investigated using jet erosion test setup in both as-cast and heat-treated conditions. The samples were characterised for hardness and microstructural properties. A new and novel non-destructive evaluation technique namely positron lifetime spectroscopy has also been used for the first time to characterise the microstructure of the material in terms of defects and their concentration. We found that the hardness decreases irrespective of the sample condition when the mould type is changed from metal to sand, On the other hand, the erosion volume loss shows an increasing trend. Since the macroscopic properties have a bearing on the microstructure, good credence is obtained from the microstructural features as seen from light and scanning electron micrographs. Faster cooling in the metal mould yielded fine carbide precipitation on the surface. The defect size and their concentration derived from positron method are higher for sand mould compared to metal mould. Lower erosion loss corresponds to smaller size defects in metal mould are the results of quicker heat transfer in the metal mould compared to the sand mould. Heat treatment effects are clearly seen as the reduced concentration of defects and spherodisation of carbides points to this. The erosion loss with respect to the defects size and concentration correlate very well. [ABSTRACT FROM AUTHOR]

Abstract: The microstructural changes in human hair due to chemical and photochemical oxidative processes have been monitored in terms of free volume employing Positron Annihilation Lifetime Spectroscopy (PALS). The results show that upon UV exposure the photosensitive amino acid residues present in the amorphous domains of virgin/bleached hair cross-link under ambient conditions. Further, the bleached hair readily undergoes photodamage in comparison with the virgin hair implying the diminished photoprotective action of the melanin granules within it. Swelling of hair fiber was evident in the early stages of UV exposure (<300h), bleaching, and humidification subsequent to irradiation. Swelling and cross-linking were the two main processes observed following UV exposure, which oppositely affect the free volume holes size. Supplementary techniques such as DSC and XRD were used to support/extend the interpretation of the PALS results. The UV irradiation resulted in reduction of the average crystallite size in hair, which is attributed to the possible fragmentation of protein domains. The present work is the first positron lifetime measurement on human hair that demonstrates the ability of PALS to provide information on hair damage at molecular level, a vital input for cosmetic industry and applicable to biopolymers research as well. [Copyright &y& Elsevier]

Abstract: Abrasion and slurry erosion behaviour of chromium–manganese iron samples with chromium (Cr) in the range ∼16–19% and manganese (Mn) at 5 and 10% levels have been characterized for hardness followed by microstructural examination using optical and scanning electron microscopy. Positron lifetime studies have been conducted to understand the defects/microporosity influence on the microstructure. The samples were heat treated and characterized to understand the structural transformations in the matrix. The data reveals that hardness decreased with increase in Mn content from 5 to 10% in the first instance and then increase in the section size in the other case, irrespective of the sample conditions. The abrasion and slurry erosion losses show increase with increase in the section size as well as with increase in Mn content. The positron results show that as hardness increases from as-cast to heat treated sample, the positron trapping rate and hence defect concentration showed opposite trend as expected. So a good correlation between defects concentration and the hardness has been observed. These findings also corroborate well with the microstructural features obtained from optical and scanning electron microscopy. [Copyright &y& Elsevier]

Epoxy resins need modifications by rubbery additives, fillers, etc. for enhancement of their usage in various applications. This study aims to determine the mechanical properties of silicone (i.e., amine-containing poly dimethyl siloxane)-modified resins in combinations with fly ash. The mechanical properties, especially tensile/flexural strength and moduli, were determined. Amine-containing silicone (ACS) was found to weaken the epoxy resin. However, ACS-modified epoxy resin was found to tolerate the addition of a small amount of fly ash filler as it had better tensile and flexural strengths compared with the unfilled, modified resin. In contrast to this, the unmodified resin was found to have its tensile and flexural strengths deteriorated by the filler. The reason for this behaviour was speculated to be due to the ACS acting as an additional coupling agent between the resin and the filler. These properties were sought to be correlated with free volume parameters measured from Positron Annihilation Lifetime Spectroscopy. Free volume measurements appear to indicate enhanced epoxy-fly ash interactions by ACS. Scanning Electron Microscopy indicates better filler distribution in the ACS-modified resin compared with the unmodified resin. [ABSTRACT FROM AUTHOR]

Abstract: Partially miscible blends of PP/NBR and PVC/SAN with different compositions have been prepared by solvent casting and characterized by positron annihilation lifetime and differential scanning calorimetry. Phase modification in these systems has been brought about using e-beam and microwave irradiations. These changes have been studied through free-volume monitoring. The changes in free-volume parameters on e-beam and microwave irradiations on the two systems clearly show improved interaction between the blend constituents as a result of cross-linking through hydrogen bond formation. However, the free-volume data do not indicate whether the improvement in miscibility is due to changes at the interface or in the constituents of the blend. We have extended free-volume data to evaluate the hydrodynamic interaction parameter α, which is the measure of excess friction at the interface of the blend. Hydrodynamic interaction parameter shows that e-beam is a better interface stabilizer if the blends contain no polar group/groups and microwave irradiation is a better route to stabilize the interface in the case where the blend contains a polar group. [Copyright &y& Elsevier]

Abstract: The diffusion behavior of a commercial permanent liquid hair dye in human hair has been investigated using positron annihilation lifetime spectroscopy (PALS) and gravimetric sorption method. The positron technique makes it possible to non-invasively characterize the angstrom sized free volume holes in hair, which are supposed to be express pathways for diffusion of small molecules. The o-Ps lifetime parameters τ 3 and I 3 decrease rapidly during the first 60min of sorption time. The overall decrease in o-Ps lifetime (τ 3) was well over 200ps and o-Ps intensity (I 3) drops by 3.5%. These positron results are explained in terms of dye molecules filling the free volume holes and hair morphology. The dye penetrates the cuticle rapidly, but slowly in cortex. The first hour of dyeing appears to be the most effective period of deposition of dye molecules within hair. These results are well corroborated by the sorption results which suggest that the dye diffusion is essentially a diffusion controlled (i.e. Fickian) process, with no observable relaxation effects. In the latter part of the sorption, where positron parameters remain almost constant, mass increase might be due to surface adhesion. These two stages of sorption are well separated by the positron technique. The sorption curve also yielded an average value of apparent diffusivity of the dye in hair. From this study, we conclude that the free volume theory and positron technique, widely used in polymer research, may expediently be used to understand hair properties, more importantly diffusion of dye molecules. [Copyright &y& Elsevier]

The wear resistance of high chromium iron is well recorded. However, the same is not the case as regards the use of manganese at higher percentages in high chromium irons and its influence on wear behaviour. Hence, this work highlights the slurry wear characteristics of chromium (◻ 16-19%) iron following the introduction of manganese at two levels i.e. 5 and 10%. It is known that the wear properties are dictated by the microstructural features. To alter the structure, the cooling rate of casting has been varied by adopting two different types of moulds (i.e. sand and metal) and subsequently subjecting to thermal treatment. The as-cast and heat treated samples are examined for microstructure and then evaluated for hardness and slurry erosion properties. As the manganese content is increased from 5 to 10%, the hardness showed a decrease in value both in the as-cast and heat treated conditions. The slurry erosion loss, expectedly, showed an increase irrespective of the sample condition (i.e. mould type/heat treatment adopted). The findings are corroborated with the microstructural features obtained through optical and scanning electron microscopy. [ABSTRACT FROM AUTHOR]

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]

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]

Abstract: Miscibility and phase separation in SAN/PMMA blends have been investigated using DSC, IR spectroscopy and positron lifetime spectroscopy (PLS). Single broad glass transition observed throughout the blend compositions, may be due to overlap of two glass transitions. IR measurements clearly indicate the absence of strong interactions. This supports miscibility is due to intramolecular repulsive forces in the SAN component. On the other hand, free volume data show negative deviation from linear additivity indicating the blends are miscible. The interchain interaction parameter β exhibits a complex behavior and the extent of miscibility is not revealed. Following Wolf’s treatment, we have evaluated the geometry factor γ and hydrodynamic interaction parameter α and found α is a suitable parameter in predicting the miscibility window. The cloud points in SAN/PMMA blends increase with decreasing PMMA content. The change in free volume size correlates well with the observed change in cloud point. [Copyright &y& Elsevier]

Abstract: The gas permeability coefficient of nano and micro composites of natural rubber, carboxylated styrene butadiene rubber and 70:30 natural rubber/carboxylated styrene butadiene rubber blend membranes has been investigated with special reference to type of filler, gases, filler loading and pressure. The layered silicates such as sodium bentonite and sodium fluorohectorite were the nanofillers used and the conventional micro fillers were clay and silica. Latex nanocomposites were characterized by X-ray diffraction technique. The dispersion of layered silicates in the polymer matrix was analysed using transmission electron microscopy. The fluorohectorite silicate showed excellent dispersion in natural rubber matrix. The effect of free volume on the gas barrier properties was investigated by positron annihilation lifetime spectroscopy. It was observed that due to the platelet like morphology and high aspect ratio of layered silicates, the gas barrier properties of nano filled latex membranes were very high. The crosslink density values and extent of reinforcement were estimated in order to correlate with the gas barrier properties. The oxygen/nitrogen selectivity of these membranes were investigated. The diffusion of gas molecules through the polymer was determined by time-lag method and diffusion selectivity of the membranes was computed. [Copyright &y& Elsevier]

Positron lifetime measurements have been performed to investigate the free volume dependence of the mechanical properties of Epoxy/poly methyl methacrylate (PMMA) blends of varying composition of PMMA (2.5, 5, 7.5, 10, 12.5, 15, and 17.5 wt%). The mechanical properties of the blends have been evaluated according to the (ASTM) standard. The positron results indicate that the mechanical properties like tensile strength and surface hardness have a significant dependence on the free volume of the blends. It is also found that the blends of the present study show positive deviation from the familiar linear additivity rule suggesting the immiscible nature of the blends. Further, up to 5-wt% of PMMA in the blend, an increase in relative fractional free volume correlates well with a decrease of tensile strength. [ABSTRACT FROM AUTHOR]

Abstract: The blends of poly(trimethylene terephthalate) (PTT) and ethylene propylene diene monomer (EPDM) with different composition have been studied by positron lifetime technique (PLT) and differential scanning calorimetric (DSC) measurements. The DSC results for the blends of 50/50 and 40/60 show clear two glass transition temperatures indicating two-phase system. No melting point depression was observed for the blend system, which strongly supports the incompatibility. From the positron results an increase in free volume hole size and its concentration has been observed with the increase in EPDM content of the blend which indicates further that there is coalescence of free volumes of EPDM with the PTT to some extent and phase separation behavior continues. Another interesting aspect is that the relative fractional free volume exhibits neither negative nor positive deviation from the log additivity rule. It agrees well with the log additivity rule. The interchain interaction parameter evaluated from these results show some complex behavior. XRD results show the decrease in crystallinity of the blend with the increase in fractional free volume with the increase in concentration of EPDM. [Copyright &y& Elsevier]

Studies thermally induced microstructural changes in natural polymer-Nistari silk fibers using positron lifetime measurements. Variation in positron results indicating structural changes in Nistari silk; Measurement of activation energies for crystalline and amorphous regions; Indication of a possible change in structure of cotton fibers owing to cross-linking.

The free volume modifications in carbon-ion irradiated poly (ethylene terephthalate) (PET) have been investigated using positron lifetime method and sorption kinetics by the gravimetric method. The positron results indicate the formation of linear tracks and free radicals. Iodine sorption suggests Longmuir type of filling of the free volume sites by iodine in the initial stages of sorption, and in the later stages, swelling and conformational changes dominate. Using dual sorption model, diffusion- and relaxation-controlled sorption have been separated. Further, it has been found that the diffusion process deviates from Fick''s law and hence from Fujita''s free volume theory for both virgin and C-ion irradiated PET. [Copyright &y& Elsevier]

The influence of vinylidenefluoride (3% composition) on the physical ageing of poly(chlorotrifluoroethylene) at 70 °C has been investigated using the positron annihilation lifetime technique. Both the ortho-positronium (o-Ps) pick-off lifetime and its intensity show a systematic variation with ageing time. The o-Ps intensity exhibits non-exponential character which can be fitted with two additive exponential decay curves and the free volume is found to exhibit the Doolittle type of free volume relaxation. The relaxation times were evaluated from the structural relaxation function and the non-exponentiality parameter was estimated using the Kohlrausch–Williams–Watts (KWW) function, which indicates the deviation from exponential relaxation. Based on the relaxation times, the activation energies calculated seems to label the different kinetic units/irregularity in the chain backbone of PCTFE structure participating in the relaxation process. Physical ageing seems to yield close packing of polymer chains. [Copyright &y& Elsevier]

Positron lifetimes in C[sub 60] and C[sub 70] fullerenes have been measured using Positron Lifetime technique. The analyzed lifetime spectra yields a single lifetime component in agreement with the earlier measurements. XRD measurements have also been used to characterize the fullerene samples. The C[sub 60] and C[sub 70] fullerenes have regular crystallographic face centered cubic structure with lattice constant a = 14.149 Å and 14.903 Å respectively in good agreement with the literature data. The present positron results clearly support the conclusion that positrons do not form positronium in fullerenes. [ABSTRACT FROM AUTHOR]

Glass-fiber reinforced epoxy nanocomposites are widely used in high voltage outdoor applications. One of the serious problems of outdoor insulation is the surface tracking and erosion that leads to premature failure of insulation. In this paper free-space length, surface energy and surface tracking of epoxy composites with nano alumina, silica and micro alumina trihydrate fillers and unidirectional glass fiber reinforcement are discussed. Quantitative interfacial analysis has been used by determining the freespace length of the composites. The results of tracking are explained on the basis of contact angle measurements and the concept of surface energy is used to substantiate the results. The time-to-track and surface erosion of dry and water treated nanocomposites are determined by the inclined plane tracking and erosion method. The experimental results have revealed that the hydrophobic nature of glass epoxy composites improves with addition of fillers. The surface energy, wettability and interaction parameters show reduction with the addition of fillers. It is observed that the Glass Epoxy composite with combination of nano alumina, silica and micro ATH fillers exhibits good thermal, electrical and mechanical properties with improved tracking and erosion resistance. [ABSTRACT FROM AUTHOR]

The glass resistive plate chamber (RPC) detector materials were exposed to 8 MeV electron beam from 20 to 100 kGy in steps of 20 kGy. In order to study the electron beam irradiation-induced effects in glass RPC detector material, positron annihilation lifetime spectroscopy (PALS), X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic investigations were carried out. PALS analysis at lower electron doses indicates the increased void size with the creation of additional sites in the glass network. This is attributed to the breakage of Si-O bonds at the regular tetrahedral sites of Si-O-Si up to 40 kGy. The reduced void size at higher irradiation doses indicates the increased chemical bonding between the tetrahedral sites of Si-O-Si and hence increases the short-range order in the silica glass. These changes are complement with the XRD, FTIR results and the measured electrical conductivity. The variation of AC conductivity with frequency obeys Jonscher power law in all the electron irradiation doses at room temperature. The variation in optical band gap energy from the ultraviolet-visible (UV-Vis) spectra inferred the elimination of defects accumulation at higher irradiation doses due to the glass network close packing. [ABSTRACT FROM AUTHOR]

The paper reports the results of moisture and filler induced effects on the dynamic mechanical properties of glass fiber reinforced epoxy hybrid composites. The rate of water diffusion into the composites has been determined to understand the effect of moisture on the dynamic mechanical properties. Significant differences in the moisture uptake properties of the composites are observed which induce changes in storage modulus (E′), loss modulus (E″), and damping factor (tan δ). It is also observed that water diffusion depends on the free volume content of the hybrid composites. Results of this study indicate that hybrid composites with combination of micro and nanofillers possess good dynamic mechanical properties in presence of moisture at higher temperatures. [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]

Abstract: Nanocomposite membranes (NCMs) of sodium alginate/poly(vinyl pyrrolidone) blend polymers incorporated with varying concentrations of phosphotungstic acid (H3PW12O40) (PWA) nanoparticles have been prepared and used in ethanol dehydration by the pervaporation (PV) technique. Effects of filler concentration, temperature and feed water composition have been investigated to understand the PV performance of the membranes in terms of separation factor and flux. Surface morphology/energy, free volume, collective and complex range of interactions between the permeants and membranes as well as membrane swelling were studied. Arrhenius activation parameters for diffusion and permeation have been estimated. Membranes were characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), and environmental emission scanning electron microscopy (ESEM). Size of the PWA nanoparticles was determined by a particle size analyzer. Surface free energies calculated from contact angles as well as free volume and fractional free volume parameters obtained from positron annihilation lifetime spectroscopy (PALS) have been used to understand the membrane transport phenomenon in terms of membrane–permeate interactions. [Copyright &y& Elsevier]

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]

Abstract: The influence of dynamic vulcanization and blend composition on the free volume properties of polypropylene (PP)/nitrile butadiene rubber (NBR) blends has been studied by using a novel technique based on positron annihilation lifetime spectroscopy (PALS). The non-vulcanized blends presented an increase of average free volume size holes and relative fractional free volume, which is an indication of incompatibility between the blend components. The dynamic vulcanization decreased the PALS parameters because of the presence of the crosslinking both inside the rubber phase and, probably, at the interface. In spite of the significant difference in PALS parameters observed as a function of the vulcanization, the mechanical properties were similar for non-vulcanized and vulcanized blends of similar composition. [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]

Resistive Plate Chamber (RPC) detector materials viz., Asahi and Saint Gobain float glasses were exposed to 500 keV and 1 MeV oxygen ions at diverse fluences. Positron Annihilation Lifetime Spectroscopic (PALS) investigations were carried out to explore the ion implantation induced microstructural modifications in these glasses. Positron lifetime parameters at lower ion implantation fluences suggests the breakage of Si O bonds at the regular tetrahedral sites of Si O Si and the displacement of molecules due to the formation of track inside the silicate glass structure in Asahi glass samples. In both the glasses, the reduced void size at higher ion implantation fluences indicates the increased chemical bonding between the tetrahedral sites and hence increases the short range order. The local temperature induced diffusion followed by trapping of ions in the interior glass voids is predominant at higher fluences. The microstructural modifications and electrical conductivity in both the glasses were well correlated with the measured free volume parameters. The variation in optical band gap from the UV–Vis absorption edge inferred the possibility of strain mismatch in the glass network by the elimination of defects at higher implantation fluences. This is complementary with Fourier Transform Infrared (FTIR) results. [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]

Epoxy resin based nanocomposites with silica (SiO2), alumina (Al2O3) and zinc oxide (ZnO) as nano fillers were fabricated to investigate the relationship between the polarization and depolarization current. The polarization and depolarization current, charge carrier mobility, absorption current and nano size free volume cavities of nano dielectric epoxy composites and their interrelation are discussed. It is observed that the current magnitude increases in the three nanocomposites with loading of nano SiO2, Al2O3 and ZnO and the peak width of each composite is greater than that of pure epoxy. Free volume studies are carried out using positron annihilation lifetime spectroscopy (PALS). From the results it is observed that molecular polarizability decreases and charge carrier mobility increases with the incorporation of SiO2, Al2O3 and ZnO loading. This trend is typical in Al2O3, whereas in case of SiO2 the molecular polarizability is unaffected and with ZnO, molecular polarizability and charge carrier mobility decrease above 10 wt% filler. The Al2O3 nanofillers are structurally different as compared to SiO2 and ZnO fillers. It is observed that Al2O3 has more influence on polarizability of the composite. [ABSTRACT FROM AUTHOR]

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 PL (10-3 m0c). 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 FROM AUTHOR]

Abstract: The carbon fabric reinforced epoxy (C–E) with different loading of organo-modified montmorillonite (oMMT) hybrid composites were prepared using hand lay-up technique followed by autoclave curing. The effects of oMMT loading on mechanical properties and three-body abrasive wear behaviour of hybrid composites have been investigated. The three-body abrasive wear tests with different loads/abrading distances were performed at room temperature using a Rubber wheel abrasion test apparatus. Experimental results obtained from tensile tests indicate that the tensile strength and modulus of hybrid composites increases with the increment of oMMT nanoparticles. Furthermore, the C–E specimens with 5wt% oMMT loading exhibit superior tensile strength than those that do not contain any oMMT nanoparticles. The abrasive wear test results showed that the wear volume increased with increasing abrading distance and the specific wear rate decreased with increasing abrading distance/load for all hybrid composites. Among the oMMT loaded hybrid composite samples tested, 5wt% oMMT loaded hybrid composite showed a promising trend. Free volume property of the hybrid composites measured from positron lifetime spectroscopy seems to correlate well with the mechanical and wear properties. Finally, the different wear mechanisms were observed on the worn surface of the hybrid composites including micro and macro cracks, pitting, as well as debonding and breakage of the fibers by scanning electron microscopy, atomic force microscopy coupled with vision measure scope. [Copyright &y& Elsevier]

The hydrothermal synthesis of TiO2 nanoparticles on the surface of calcium aluminosilicate beads of 0·5-1·0 mm in diameter has been carried out under mild hydrothermal conditions. The advantage of immobilisation of the TiO2 nanoparticles by coating on calcium aluminosilicate beads is the ease and efficiency to recover the photocatalyst. The experimental temperature was varied from 150 to 220°C and the experimental duration was 24 h with an autogenous pressure in 1M HCl as solvent. A systematic characterisation of TiO2 coated calcium aluminosilicate beads was carried out by employing analytical techniques like X-ray powder diffraction, SEM, FTIR spectroscopy and positron annihilation lifetime spectroscopy. The photocatalytic treatment of toxic organic pollutants in textile effluents was studied using hydrothermally prepared TiO2 coated calcium aluminosilicate beads. The photodegradation characteristics were studied under both sunlight and ultraviolet light source on the degradation of organic pollutants. Several parameters like concentration and dilution factors of effluents, light source and intensity, initial pH of medium, experimental duration and catalyst loaded into the aqueous medium of textile effluent were studied. The degradation reaction was optimised with respect to the experimental duration and catalytic loaded. The reduction in the chemical oxygen demand (COD) and %T revealed the minimisation of organic pollutants along with colour removal from the textile effluent. [ABSTRACT FROM AUTHOR]

Blends of poly (vinyl alcohol) (PVA), poly-N-acyl ethyleneimine (PEI) and gelatin (PVA/ PEI/Gel) in the weight ratios 100/0/2, 95/5/2, 90/10/2, 85/15/2, 80/20/2 and 70/30/2 were prepared by solution casting method. The effects of poly (ethylene imine) component in the blend and microwave irradiation on the mechanical and microstructural properties have been investigated using various techniques along with Positron Annihilation Lifetime Spectroscopy (PALS). We observed tremendous improvement in mechanical properties after microwave irradiation for 60 s in 5 wt% of PEI component blend. These results are supported by the SEM data as well the optical data. The free volume data from positron results showed minimum free volume at 5 wt% of PEI after 60 s of irradiation due to cross linking through hydrogen bond formation and possible estrification among the blend components. These results correlate well the mechanical properties like tensile strength and modulus. [ABSTRACT FROM AUTHOR]

Polymer-Zeolites composites have been prepared, using castor oil based polyurethane (PU) as a host and AlPO4-5 as particulate filler. The prepared PU/zeolite composites have been characterized for mechanical properties such as tensile strength and tensile modulus. These PU composites exhibited an improved mechanical performance compared to the unfilled PU. Thermo gravimetric analyzer (TGA) curve shows that all the chain-extended PUs are stable up to 250 °C and maximum weight loss occurs at 490 °C. The thermal stability of composites increases with increase in zeolite content. Microcrystalline parameters and micro voids of composites have been measured by using wide-angle X-ray scattering (WAXS) and Positron Annihilation Lifetime (PALS) methods respectively. The microcrystalline parameters and micro-voids from PALS indicate the interaction of the filler with the matrix is stronger beyond 5% of the filler which reflect the mechanical performance as well. Surface morphology of composites has been studied using Scanning Electron Microscopy (SEM). The photomicrograph of SEM indicates a uniform distribution of zeolite filler in the PU matrix. [ABSTRACT FROM AUTHOR]

Abstract: A new photocatalyst titania:activated carbon (TiO2:AC) composite was prepared by impregnating anatase type TiO2 nanoparticulates onto the activated carbon surface through a mild hydrothermal route. A varied ratio of TiO2 to AC was considered for impregnation. As-prepared TiO2:AC composite was characterized by various techniques such as powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), BET surface area and positron annihilation lifetime spectroscopy (PALS). Powder XRD results showed the persisting nature of anatase phase of TiO2 deposited on the activated carbon surface. The BET, FTIR and PALS results revealed the impregnation threshold. The TiO2 particulates were well adhered and uniformly dispersed on the carbon surface as confirmed by SEM. [Copyright &y& Elsevier]

Microstructural studies on BaCl2 doped polyvinyl alcohol (PVA) polymer films were carried out using density, PAL and dielectric measurements at room temperature. The positron annihilation studies on these samples shows considerable effect on the PVA microstructure due to doping and is understood by invoking the chemical reaction between Ba2+ ions of BaCl2 with OH groups of PVA via intra/inter molecular hydrogen bonding, which forms the complex. This complex formation modifies the free volume content in the amorphous fraction, and results in an enhancement of the polymer crystallinity. At higher dopant concentrations, the number of such complexes increases, and ends up with the formation of dopant aggregates or agglomerates leading to certain phase separation into a polymer-rich phase and a dopant-rich phase. These phase separations are thought to be due to the existence of two or more crystalline phases within the polymer matrix. The XRD study also supports this enhancement of PVA crystallinity due to doping. The electrical studies on the doped PVA reflects that the complex formation due to doping affects the microstructure and hence the dielectric properties including the dc and ac conductivities of the polymer. All of these observed results were analyzed and understood based on the microstructural modification of PVA as a function of dopant concentrations. [ABSTRACT FROM AUTHOR]

The photocatalytic degradation of indigo carmine dye was studied using hydrothermally prepared TiO2 impregnated activated carbon (TiO2 : AC). A comparison between the degradation of the indigo carmine dye using commercial TiO2 and TiO2 : AC revealed the efficiency of the title compound. The degradation reaction was optimized with respect to the dye concentration and catalyst amount. The reduction in the chemical oxygen demand (COD) revealed the mineralization of dye along with colour removal. The active compound like TiO2 was impregnated onto the activated carbon surface under mild hydrothermal conditions (< 250°C, P ∼ 40 bars). The impregnated activated carbon samples were characterized using powder X-ray diffraction (XRD) and scanning electron microscope (SEM). [ABSTRACT FROM AUTHOR]

Structural relaxation in high-density virgin polyethylene and silver oxide doped polyethylene has been investigated using positron annihilation lifetime technique at 30 °C and 100 °C ageing temperatures. The ortho-positronium (o-Ps) pick-off lifetime and its intensity show no changes with isothermal ageing time for the virgin sample at 30 °C. In the case of the doped sample at 30 °C, the o-Ps intensity shows exponential relaxation in the short-time range. At 100 °C, the o-Ps lifetime remains almost constant, whereas the o-Ps intensity exhibits an exponential character in the virgin and doped samples, which can be fitted with exponential decay curves. The relaxation times have been evaluated from the structural relaxation function constructed using o-Ps intensity values, and the stretching exponent β has been estimated using the Kohlrausch–Williams–Watts (KWW) function. Positron results indicate that the stretching exponent β seems to be temperature dependent. [ABSTRACT FROM AUTHOR]

The effects of γ-irradiation on the methanol diffusion behaviour in polycarbonate have been investigated by UV-visible, Fourier Transform Infra-red (FTIR) Spectroscopy, Positron Annihilation Lifetime Spectroscopy (PALS), Differential Scanning Calorimetry (DSC), Sorption, and Optical Microscopy. Positron results show that the free volume size and its content decreases after γ-irradiation which is due to cross-linking of chains. The cross-linking process is further confirmed by DSC measurements, which indicate an increase in glass transition temperature (Tg) after γ-irradiation. Sorption results reveal that methanol diffuses faster in virgin polycarbonate as compared to cross-linked polycarbonate (after gamma irradiation) in agreement with the results of supplementary techniques. Interestingly, the optical microscopic examination of the sample surfaces provides clear evidence of decreased micro-crack formation in γ-irradiated polycarbonate as compared to the virgin sample. This decrease in crack formation can be related to the decrease in the rate of methanol diffusion. [ABSTRACT FROM AUTHOR]

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]

Structural relaxation in UV irradiated poly (ethylene terephthalate) (PET-UV) has been investigated using positron lifetime techniques. Positron lifetime results show that the structural relaxation processes in PET-UV encompass three different time regimes, unlike the unirradiated poly (ethylene terephthalate) (PET) where only two relaxation times were observed. The relaxation functions constructed from the measured ortho positronium intensity, I3, exhibit non-exponential character that can be best fitted with two additive exponentials. To determine the extent of deviation from exponential relaxation, we have used the Narayanaswamy model (KWW function) and evaluated the stretching parameter β. From the relaxation times derived from the exponential decay curves, the activation energies have been calculated and from these activation energies it seems possible to label the different kinetic units of the UV irradiated poly (ethylene terephthalate) structure participating in the relaxation processes. [Copyright &y& Elsevier]

Positron lifetime and gravimetric measurements of iodine sorption and diffusion behaviour in electron-irradiated polycarbonate and un-irradiated polycarbonate are investigated. The increase in ortho-positronium lifetime on electron-irradiation shows that scission of carbonate groups in the main-chain and formation of free radicals is the predominant process. The UV absorption measurement supports this. The free volume in polycarbonate after electron-irradiation seems to be not composed of independent pores but of interconnected channels. The positron results on iodine diffusion in un-irradiated polycarbonate shows a slower diffusion rate, whereas in electron-irradiated polycarbonate faster diffusion is observed. The gravimetric measurement of iodine diffusion attains an early saturation in electron-irradiated polycarbonate as compared to un-irradiated polycarbonate although in both cases the diffusion is nearly Fickian. An exponential type of correlation has been observed between fractional free volume and diffusion coefficient validating Fujita''s free volume theory for un-irradiated and electron-irradiated polycarbonate. [Copyright &y& Elsevier]