Mean Free Volume Research Articles

Surface Microstructure Study on Corona Discharge-Treated Polyethylene Using Positron Annihilation Spectroscopy.

The microstructure and chemical properties of the corona discharge process could provide an effective method for predicting the performance of high-voltage cable insulation materials. In this work, the depth profile of the microstructure and chemical characteristics of corona discharge-treated PE were extensively investigated using Doppler broadening of position annihilation spectroscopy accompanied with positron annihilation lifetime spectroscopy, attenuated total reflectance Fourier transform infrared spectra, Raman spectra and contact angle measurement. By increasing corona discharge duration, the oxygen-containing polar groups, including hydroxyl, carbonyl and ester groups, strongly contribute to the deterioration of hydrophobicity and the enhancement of hydrophilicity. And the mean free volume size, with a broadening distribution, decreases slightly. The line shape S parameter decreases because of the decrease in free volume elements and the appearance of oxygen-containing groups. Also, the thickness of the degradation layer, determined from the S parameter with positron injection depth, increases and diffuses into the PE matrix. A linear S-W plot within the degradation layer of different corona treatment duration samples indicates the defect type does not change. The S parameter decreases and the W parameter increases with an increasing corona duration. Using a slow positron beam, the nondestructive probe can be used to profile the microstructure and chemical environment across the corona discharge damage depth, which is beneficial for investigating the surface and interfacial insulation materials.

Investigating the Free Volumes as Nanospaces in Human Stratum Corneum Lipid Bilayers Using Positron Annihilation Lifetime Spectroscopy (PALS).

This work is the first one that provides not only evidence for the existence of free volumes in the human stratum corneum but also focuses on comparing these experimental data, obtained through the unique positron annihilation lifetime spectroscopy (PALS) method, with theoretical values published in earlier works. The mean free volume of 0.269 nm was slightly lower than the theoretical value of 0.4 nm. The lifetime τ3 (1.83 ns with a coefficient of variation CV of 3.21%) is dependent on the size of open sites in the skin. This information was used to calculate the free volume radius R (0.269 nm with CV 2.14%), free volume size Vf (0.081 nm3 with CV 4.69%), and the intensity I3 (9.01% with CV 10.94%) to estimate the relative fractional free volume fv (1.32 a.u. with CV 13.68%) in human skin ex vivo. The relation between the lifetime of o-Ps (τ3) and the radius of free volume (R) was formulated using the Tao-Eldrup model, which assumes spherical voids and applies to sites with radii smaller than 1 nm. The results indicate that PALS is a powerful tool for confirming the existence of free volumes and determining their size. The studies also focused on describing the probable locations of these nanospaces in SC lipid bilayers. According to the theory, these play an essential role in dynamic processes in biological systems, including the diffusion of low-molecular-weight hydrophobic and moderately hydrophilic molecules. The mechanism of their formation has been determined by the molecular dynamics of the lipid chains.

Effect of electron beam irradiation on hole structure of cellulose acetate membrane

Cellulose acetate (CA) is one of the most popular biomaterials used for filtration membranes in water treatment.In this study, the CA membranes immersing in water were irradiated by electron beam, and the hole structure of CA membranes at different irradiation doses was investigated. The SEM pictures show the combination of micro-meter sized pores in CA membrane during the irradiation process. The electrochemical impedance spectroscopy(EIS) results reveal the membrane resistance decreases with the irradiation dose, which implies easier ion permeation. The positron annihilation lifetime measurement (PAL) results indicate the mean free-volume hole size becomes smaller with increasing irradiation dose. The above results demonstrate that electron beam irradiation would lead to chain scission of CA, and then the formation of new pores and pores combination, which provides more channels for ion permeation. FTIR results suggest stronger hydrogen bonding in CA after the irradiation in water. The differential scanning calorimetry (DSC)results indicate that the crystallinity has been enhanced with the irradiation dose up to 10 kGy and reduces in the range from 10 kGy to 80 kGy. The results could provide the clues explaining the performance deterioration of CA membrane during treating radioactive waste water.

Molecular simulation of CO2 capturing by dual functionalized phosphonium-based amino acid ionic liquids

Various solvents have been proposed considering the importance of CO2 gas removal from the environment. Over the past few decades, ionic liquids (ILs) have elicited much attention due to their unique properties. In this regard, capturing the CO2 gas by phosphonium-based amino acid ILs (AAILs) was studied by molecular dynamics (MD) simulation. The effect of cation functionalization was studied. The anion was glycinate, [GLY]-, and the cation was tetrabutylphosphonium, [P4444]+, functionalized by different functional groups including acidic (−COOH), alcoholic (−OH), amine (−ΝΗ2), and ether (−OCH3). Density, absorption energy, radial distribution function (RDF), mean square displacement (MSD), concentration profile, free volume, and fractional free volume were under investigation. According to density values calculated from MD simulation, functionalized AAIL with a carboxylic acid group ([P4444COOH][Gly]) is the most concentrated system with the maximum interaction energy between AAIL and the trapped CO2 gas equal to − 1.917 kcal.mol−1. In addition, the lowest volume variation was observed through this physical absorption. RDF analysis reveals that anion interaction with CO2 gas is the most considerable one in the case of [P4444COOH][Gly] AAIL. The CO2 uptake is 2:1 for functionalized AAILs that shows cation functionalization improves CO2 gas absorption capacity; each mole of [P4444COOH][Gly] AAIL is capable of surrounding 2.11 mol of CO2. Finally, the gas diffusion coefficient is the lowest one in [P4444COOH][Gly] AAIL as the solvent-free volume is observed as a continuous channel to trap CO2 gas with the lowest gas diffusivity parameter.

Effect of composition and coordination number on some fundamental parameters in the Ge-Se glass

Chalcogenide glasses of GexSe100-x (x=10, 15, 20, 25 and 30 at.%) glasses were prepared by vacuum melting. An empirical relation between the glass transition temperature (Tg) and <r> is proposed by applying the Gibbs-Di Marzio equation for the Tg of a crosslinked polymer as a function of cross-linked density. We found a good agreement with the experimental result of Tg for GexSe100-x glasses. Several parameters such as mean atomic volume density, compactness, and free volume percentage which are more sensitive to the structure network changes were calculated. Their variation is discussed in connection with the proposed structural model. The variation of the molar volume and Tg with <r> indicates the coexistence of topological and chemical ordering effects. With the structural modification, the number of lone-pair decreases, and the covalent coupling of the structural network increases with increasing Ge content, due to the increases in the crosslinked between Ge and Se bridge.

Influence of Crosslinking Extent on Free Volumes of Silicone Rubber and Water Diffusion after Corona Discharge.

Silicone rubber is widely used as an insulating material. In this article, silicone rubber samples were prepared by varying the content of crosslinker (2,5-bis(tert-butyl-peroxy)-2,5-dimethylhexane, DBPMH), and the free volume holes in the samples were investigated by means of positron annihilation lifetime spectroscopy (PALS) measurement. The surface chemical structure, surface micromorphology and water diffusion of the samples after corona discharge treatment were studied by FTIR, SEM and EIS measurements, respectively. As the crosslinker weight ratio increased from 0.2 wt.% to 1.5 wt.%, the mean free volume hole size first decreased and then remained unchanged. However, the concentration of free volume holes did not vary as the crosslinker weight ratio increased. SEM morphologies show that surface cracks were produced on samples having high crosslinking levels after corona treatment. The water diffusion coefficient of samples after corona treatment increased from 3.13 × 10−10 cm2 s−1 to 17.68 × 10−10 cm2 s−1 in the initial immersion period, as the crosslinker weight ratio increased from 0.2 wt.% to 3.0 wt.%. The results indicated that deterioration of samples with high crosslinking levels were more serious and water repellency more easily lost. The corona resistance ability of low crosslinking level silicone rubber stems from internal low molecular weight molecules.

Development of Tg-less epoxy thermosets by introducing crosslinking points into rigid mesogenic moiety via Schiff base-derived self-polymerization

Novel glass-transition-temperature-less (Tg-less) epoxy thermosets were prepared by a Schiff base (CH=N)-derived self-polymerization of mesogenic epoxy. The self-polymerization mechanism was verified by differential scanning calorimetry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The epoxy–CH=N addition reaction formed a new tertiary amine, introducing a crosslinking point into the rigid mesogenic moiety. Dynamic mechanical analysis of the cured system showed a slight α-relaxation in tanδ, and a high storage modulus was maintained at > 250 ℃. Also, no drastic increase in the coefficient of thermal expansion related to the glass-transition behavior was observed. The results suggested that the crosslinking point formed in the rigid mesogenic moiety effectively suppressed the thermal motion of networked chains, resulting in Tg-less behavior. An imidazole catalyst was used to enhance the self-polymerization reactivity. The imidazole content effect on the temperature-dependency of the mean free volume in the network structure was investigated by positron annihilation lifetime spectrometry.

Nano-Porous-Silicon Powder as an Environmental Friend.

Nano-porous silicon (NPS) powder synthesis is performed by means of a combination of the ultra-sonication technique and the alkali chemical etching process, starting with a commercial silicon powder. Various characterization techniques {X-ray powder diffraction, transmission electron microscopy, Fourier Transform Infrared spectrum, and positron annihilation lifetime spectroscopy} are used for the description of the product’s properties. The NPS product is a new environmentally friendly material used as an adsorbent agent for the acidic azo-dye, Congo red dye. The structural and free volume changes in NPS powder are probed using positron annihilation lifetime (PALS) and positron annihilation Doppler broadening (PADB) techniques. In addition, the mean free volume (VF), as well as fractional free volume (Fv), are also studied via the PALS results. Additionally, the PADB provides a clear relationship between the core and valence electrons changes, and, in addition, the number of defect types present in the synthesized samples. The most effective parameter that affects the dye removal process is the contact time value; the best time for dye removal is 5 min. Additionally, the best value of the CR adsorption capacity by NPS powder is 2665.3 mg/g at 100 mg/L as the initial CR concentration, with an adsorption time of 30 min, without no impact from temperature and pH. So, 5 min is the enough time for the elimination of 82.12% of the 30 mg/L initial concentration of CR. This study expresses the new discovery of a cheap and safe material, in addition to being environmentally friendly, without resorting to any chemical additives or heat treatments.

Role of moisture in photo-ageing -macromolecular architecture evolution of acrylic-urethane network

In this work, the role of moisture in photo-ageing was discussed for the case of an acrylic-urethane network. Ageing behaviours were characterised by Fourier transform infra-red spectroscopy, positron annihilation lifetime spectroscopy, sol-gel analysis, and differential scanning calorimetry. Two common features between dry and wet photo-ageing, namely, decrease in the mean free volume and increase in the glass transition temperature were observed as photo-oxidation progressed. The characteristics of the final internal structure of the wet photo-aged sample differed from those of the dry photo-aged sample. Although the dry photo-aged samples suggested network densification due to extensive crosslinking formation, wet photo-ageing led to an inhomogeneous structure wherein the average molar mass between crosslinks (at a scale of several nanometres) increased and some domains crosslinked at the sub-nanoscale. Considering the physical (plasticisation) and chemical (hydrolysis) effects induced by water, a possible mechanism for the evolution of the macromolecular architecture was proposed for photo-ageing in dry and wet environments.

Tuning Selectivities in Gas Separation Membranes Based on Polymer-Grafted Nanoparticles.

Polymer membranes are critical to many sustainability applications that require the size-based separation of gas mixtures. Despite their ubiquity, there is a continuing need to selectively affect the transport of different mixture components while enhancing mechanical strength and hindering aging. Polymer-grafted nanoparticles (GNPs) have recently been explored in the context of gas separations. Membranes made from pure GNPs have higher gas permeability and lower selectivity relative to the neat polymer because they have increased mean free volume. Going beyond this ability to manipulate the mean free volume by grafting chains to a nanoparticle, the conceptual advance of the present work is our finding that GNPs are spatially heterogeneous transport media, with this free volume distribution being easily manipulated by the addition of free polymer. In particular, adding a small amount of appropriately chosen free polymer can increase the membrane gas selectivity by up to two orders of magnitude while only moderately reducing small gas permeability. Added short free chains, which are homogeneously distributed in the polymer layer of the GNP, reduce the permeability of all gases but yield no dramatic increases in selectivity. In contrast, free chains with length comparable to the grafts, which populate the interstitial pockets between GNPs, preferentially hinder the transport of the larger gas and thus result in large selectivity increases. This work thus establishes that we can favorably manipulate the selective gas transport properties of GNP membranes through the entropic effects associated with the addition of free chains.

Exploring the potential role of pyrazoline derivatives in corrosion inhibition of mild steel in hydrochloric acid solution: Insights from experimental and computational studies

Iron and its alloys are commonly used materials in petroleum refining facilities. However, poor corrosion resistance is always a disturbing problem for these industries. Herein, we demonstrated the utility of two pyrazoline derivatives (PYRs), namely, 2-(4-(4,5-dihydro-3-(4-methoxyphenyl)-1H-pyrazol-5-yl)phenoxy)acetic acid (PYR-1) and 2-(4-(4,5-dihydro-3-p-tolyl-1H-pyrazol-5-yl)phenoxy)acetic acid (PYR-2) for enhancing mild steel (MS) resistance in 1.0 M HCl using chemical, electrochemical, scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and computational techniques. Weight loss measurements revealed that the optimum concentration of inhibitors is 5 mM. The maximum inhibition efficiencies (based on electrochemical results) were obtained 94% and 88% for PYR-1 and PYR-2, respectively. Pyrazolines retard corrosion at room temperatures and show high inhibition efficiency at higher temperatures, (above 90% at 333 K). XPS results showed that these compounds could effectively inhibit acid attack through physical and chemical adsorption on the metal surface. PYRs adsorption onto the steel surface follows Langmuir adsorption model. Electrochemical results revealed that the new compounds could exhibit excellent corrosion inhibition performance and displayed mixed-type inhibition. The performances of inhibitor films and the potential mechanisms were also investigated theoretically using MD simulation, radial distribution function (RDF), mean square displacement (MSD) and free volume theory. The present results will be helpful to uncover the versatile importance of pyrazoline compounds in the corrosion inhibition process.

Information Contained in Molecular Motion

The equivalence between information and entropy is used to interpret the entropy of a molecular gas as missing information about its internal state of motion. Our considerations show that thermodynamic information is principally composed of two parts which continually change in the course of gas-kinetic collisions. While the first part relates to energy carried by the individual molecules in the form of kinetic energy and in internal excitations, the second relates to information concerned with the location of the molecules within their own mean-free volumes. It is shown that this second kind of information is generated in gas-kinetic collisions and rapidly deteriorated and lost by quantum mechanical dispersion until it is re-gained in follow-on collisions. It is proposed that gas-kinetic collisions can be regarded as measurement processes in which information is continually gained, deteriorated and erased. As these processes occur naturally without any human intervention, it is argued that thermodynamic information—like entropy—fully qualifies as an objective physical quantity.

The Influence of Bond Angle on Thermophysical Properties of Three-Center Lennard-Jones Fluids: Computer Simulation and Theory

Abstract We carry out extensive computer simulations to study the phase equilibrium, thermodynamics, and diffusion coefficient of three-center Lennard-Jones (3CLJ) fluids with an emphasis on the effects of bond angle on these properties. We take into account several bond angles ranging from θ 0 = 60 to 180 degrees and two equilibrium bond elongations le = 1.0 and 0.5 (in Lennard-Jones length unit). Moreover, we study the fully flexible (FF) 3CLJ fluids for molecules with bond length 1.0. Gibbs ensemble Monte Carlo (MC) simulations are performed to compute the densities of the vapor-liquid coexisting phases and the vapor pressure, and direct three-phase (vapor-liquid-vapor) molecular dynamics (MD) simulations are carried out to calculate the surface tension. We then apply constant NVT MC simulations to obtain the internal energy, the pressure, and the pair correlation function, and utilize equilibrium MD simulations to compute the diffusion coefficient of systems with le = 1.0. In addition to MD simulations, the modified Cohen-Turnbull (mCT) theory is used to to compute the diffusion coefficient and the mean free volume appearing in the mCT relation is provided by the results of the Generic van der Waals (GvdW) theory. We show that the mCT theory is capable of reproducing the MD simulation values quite well over a wide range of density with slight overestimations at medium range. The angle dependence of different thermophysical properties are analyzed and discussed in details.

Free volume characteristics on water permeation and salt rejection of polyamide reverse osmosis membranes investigated by a pulsed slow positron beam

Polyamide thin film composite reverse osmosis membranes on porous polysulfone support were prepared using m-phenylenediamine, trimesoyl chloride and dimethyl sulfoxide (DMSO) with various contents as precursors via an interfacial polymerization. The membrane with heterogeneous multilayer structure was depth-profiled by positron annihilation lifetime spectroscopy based on a pulsed slow positron beam and the thickness of the polyamide active layer can be estimated through fitting the results of depth dependence of o-Ps intensity. The free volume characteristics in the polyamide selective layer of the membranes were evaluated and were correlated with the permeation properties. With increasing DMSO content, mean free volume size (VFV) was enlarged, which was responsible for the enhanced water and sodium chloride permeation. However, the salt rejection was significantly decreased with a slight increase in the VFV around a critical value of 88.0 A3, which was the average size of hydrated sodium and chloride ions. It was well interpreted for that the broadened free volume distribution enables an amount of larger free volumes to be involved in the salt permeation, although little change in VFV was found.

Thermodynamic and transport properties of nitrogen fluid: Molecular theory and computer simulations

Computer simulations and various theories are applied to compute the thermodynamic and transport properties of nitrogen fluid. To model the nitrogen interaction, an existing potential in the literature is modified to obtain a close agreement between the simulation results and experimental data for the orthobaric densities. We use the Generic van der Waals theory to calculate the mean free volume and apply the results within the modified Cohen-Turnbull relation to obtain the self-diffusion coefficient. Compared to experimental data, excellent results are obtained via computer simulations for the orthobaric densities, the vapor pressure, the equation of state, and the shear viscosity. We analyze the results of the theory and computer simulations for the various thermophysical properties.

Improving CO2 permeation and separation performance of CO2-philic polymer membrane by blending CO2 absorbents

To research effects of CO2 absorption capacity and type of CO2 absorbent on the CO2 separation and free-volume properties of facilitated transport membranes, two types of CO2 absorbents, namely monoethanolamine (MEA) and ionic liquids (ILs:[P66614][Triz] and [P66614][2-Op]), were adopted. The CO2 absorption capacities of MEA, [P66614][Triz] and [P66614][2-Op] were about 0.561mol CO2 per mol, 0.95mol CO2 per mol and 1.60mol CO2 per mol, respectively. All mean free-volume hole radiuses of membranes decreased after blending CO2 absorbents. After polymer membrane blended with two ILs, number of free-volume hole increased, resulting in modest increase of the fractional free volume. Both CO2 permeability and selectivity increased after blending MEA and ILs. The increasing range of CO2 permeability corresponded with CO2 absorption capacity of CO2 absorbents, and membrane blending with [P66614][2-Op] showed the highest CO2 permeability of 672.1 Barrers at 25°C. Pebax/PEGDME membrane blending with MEA obtained the highest CO2/H2 and CO2/CH4 selectivity at 17.8 and 20.5, respectively.

Free volume-related microstructural properties of lithium perchlorate/sodium alginate polymer composites

The effect of salt (LiClO4) on free volume-related microstructural, optical, and dielectric properties of lithium perchlorate (LiClO4)-doped sodium alginate (NaC6H7O6)n solid polymer electrolyte were studied using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), UV–Visible, dielectric measurements, and positron annihilation lifetime spectroscopy (PALS) techniques. The FTIR study reveal that the LiClO4 interact with the OH groups of sodium alginate (NaAlg) and forms charge transfer complex (CTC). These formed CTC within the composite film affect the optical property of the polymer composite, which was reflected from UV–Visible study. The free volume was probed by the PALS technique, which uses the o-Ps pickup lifetime τ3, as an indication of local electron density and mean free volume radius. The o-Ps pickup intensity I3, reflects the probability of o-Ps formation. The o-Ps components τ3 and I3 increases with salt concentration, which shows microstructural modifications due to the decrease in the crystallinity of the NaAlg as observed from XRD studies. Therefore, electrical studies on the doped NaAlg reveal that the ionic movement in the composites is mainly due to the segmental motion of the polymer backbone. So, the complex formation due to doping affects the free volume-related microstructure and hence the dielectric properties including the AC conductivity of the polymer composites. POLYM. COMPOS., 35:1267–1274, 2014. © 2013 Society of Plastics Engineers

TEAK VOLUME MODELLING USING MEAN TREE MEASUREMENTS

Volume prediction al ;1 known precision IS essential especially for planners to makedccisions on torcst management. Thinning planning. harvesting. timber utilisation for ali<uch activities should he planned based on economical returns. to obtain maximum benefits(mill these 111;"1made forest pl.muuionx. Based on the dominant height growth variations.Illrc(' Teak /\llles were identified. ill each teak zone several teak trees were felled and truevolurncx (tot:1I Volume and the Timber Volume) were calculated and Volume Iunctionswere developed I'm each Teak zone, These volume functions were developed using meantrCl' gruW!1l measurements 01';1 st;IIHI. Therefore it is not to he used to dctcrm inc volumesIll' iudividual trccs hut to calculate the per hector volume 01 a stand by measuring the meanp.u.unctcr values of a sl:llId.The volume 01';1 felled tree was obtained by adding volume'S of its components. In the logvolume c.ttcuiauon thc "Hubcrx" equation was used. this equation gives reliable estimateslor ;iilY sli;IJ'" of jogs other than "ncloidic shape. The Diameter at Breast Height (DBH)dlHI the tlll;" hcil-'ht or Ihe tree was recorded before felling the tree. The models tested forh: Iter rill illg were:V =;, + h*DBH2 'I' Height (I)V :=; a + h*DBH2 * Height + c* Height (2)V = a"'DBH"*(Hcight)" 0)V =;\ + h*(DBH') * Height + C*(DBH) (4)In ;I11three zones the hest rilS obtained for volume estimation was model 3. This modelhas obtained high correlation in all three zones compared to other models tested.The volume functions obtained for mean free volume estimation in three Teak zones arc:Zone I: V = .O()OO!:I * (DBH)251111 "(Height ,72-1Zone 2: V = .000102 * (DBH)I.'>O(,' *(Height) .7'15Zonc S: V = .000102 * (DBH(8~~S *(Height) .81SProceedings oftlu: Fourth Annnal Forestry and Environment Symposium /99R of the Department ofForestry and

양전자소멸 수명시간 측정을 통한 폴리머소재의 자유부피에 관한 연구

양전자소멸법은 양전자와 전자가 만나 소멸하면서 발생하는 광자로부터 물질의 상태를 간접적으로 파악하는 실험 방법이다. 본 연구에서는 다양한 분야에서 널리 사용되고 있는 폴리머인 CR, EPDM, NBR에 대하여 양전자소멸법을 통해 양전자 소멸시간을 측정하였다. 한국원자력연구원의 Na-22 선원을 이용한 양전자소멸시간측정장치를 통해 양전자소멸시간의 세가지 수명과 세기를 측정하였다. 이중 세 번째 수명성분은 폴리머의 자유부피와 직접적으로 관계된다. Tao-Eldrup 모델을 이용하여 3가지 폴리머에 대한 자유부피를 측정하였다. 그 결과 CR, EPDM, NBR의 자유부피와 상대비율은 각각 <TEX>$0.1217nm^3$</TEX>(1.910%), <TEX>$0.1478nm^3$</TEX>(5.315%), <TEX>$0.1216nm^3$</TEX>(2.638%)로 나타났다. 이를 통해 양전자소멸법의 폴리머에 대한 적용성을 확인할 수 있었으며 향후 비파괴적으로 폴리머의 특성변화를 분석하는 자료로 활용될 수 있을 것이다. Positron Annihilation Lifetime Spectroscopy is a non-destructive technique to study voids and defects in solids by the measurement of gammas from electron-positron annihilation. In this study, we measured the lifetime of CR, EPDM, NBR, all of which are widely used polymer in various fields. A conventional fast-fast coincidence system in KAERI(Korea Atomic Energy Research Institute) has been used to measure the lifetime spectra, Three lifetime components were analyzed from each lifetime spectra. According to Tao-Eldrup model equation, the size and fraction of free-volume were calculated. Mean radius and free volume fraction of CR, EPDM NBR are <TEX>$0.1217nm^3$</TEX>(1.9103%), <TEX>$0.14780nm^3$</TEX>(5.3147%), <TEX>$0.1216nm^3$</TEX>(2.6381%), respectively. Through these measurements, we identified the feasibility of the PAL system for polymer analysis.

Characterisation of proton irradiated CR-39 detector using positron annihilation lifetime spectroscopy

Abstract The damaged produced by proton beam slowed down in CR-39 polymer results in highest degree of disorder with change of free volume proprieties. Positron annihilation lifetime spectroscopy (PALS) is nowadays well recognized as powerful tool of microstructure investigations. PALS is used in order to get more information at an atomic scale of modifications induced by irradiation of polymers particularly the variation of free volume in the irradiated region. In this paper, the mean free volume hole radii and average free volume of the micro-voids in CR-39 polymer irradiated with 200 MeV therapy proton beam at different positions in spread out Bragg Peak region (SOBP) at Ithemba proton therapy facility have been determined using PALS. © 2006 Elsevier Ltd. All rights reserved.