Correlation between pulse radiolysis and positron annihilation techniques data

Abbé, J.Ch.; Duplâtre, G.; Maddock, A. G.; Talamoni, J.; Haessler, A.

doi:10.1016/0022-1902(81)80584-2

Cited by 51 publications

(21 citation statements)

References 37 publications

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“…32,33 Considering the correlations 3 previously found between the Ps inhibition constants of solutes and their reaction rate constants with the solvated electron, k(e aq -), the values of k in Table 1 would effectively correspond to k (e aq -) < 10 8 M -1 s -1 . 3,34 Qualitatively, the data appear to indicate little influence of T on k, in agreement with inhibition through scavenging of nonsolvated electrons. In contrast, if e + scavenging were involved, then the corresponding e + bound state with AOT should have a shorter lifetime than free e + .…”

Section: Resultssupporting

confidence: 64%

“…B. Lifetimes in AOT/Water/Isooctane Mixtures. In threecomponent analysis of the LS spectra, the longest lifetime due to o-Ps decay in either subphase at each temperature appears to be slightly lower than τ 3 is , irrespective of the other variables, C AOT and w 0 . The mean o-Ps lifetime should be lower than τ 3 is , as some Ps atoms should decay in the aqueous core of the micelles where τ 3 aq , τ 3 is .…”

Section: Resultsmentioning

confidence: 88%

“…As a rule, only those solutes presenting high chemical reactivity are able to interact efficiently, at moderate concentrations, with Ps within its lifetime. 3 In a second step, therefore, in an attempt to gain more detailed information on both the probe and the solutions, the LS spectra were analyzed in terms of four components. In all free parameter analyses, for all C AOT , w 0 , and T, the longest lifetime, τ 4 , appears to be very close (within 1-2σ) to τ 3 is , confirming that o-Ps in isooctane is not affected by the presence of AOT.…”

Section: Resultsmentioning

confidence: 99%

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Four-Component Analysis and Modeling of Positron Annihilation Lifetime Parameters in AOT/Water/Isooctane Microemulsions

Marques¹,

Miguel

Lima

et al. 1996

J. Phys. Chem.

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Reverse micelles are studied in sodium AOT/water/isooctane mixtures as functions of AOT concentration (C AOT ), water to AOT mole ratio (w 0 ) and temperature (T), from 294 to 333 K, using positron annihilation lifetime spectroscopy (LS). By four-component analysis of the spectra, it is possible to extract the LS parameters (intensities, I i , and lifetimes, τ i ) of the triplet positronium (o-Ps) present in the aqueous (I 3 , τ 3 ) and organic (I 4 , τ 4 ) phases. The latter lifetime is constant and corresponds with the value measured in pure isooctane, while τ 3 is remarkably lower than the value for pure water. This difference is attributed to the out-diffusion of o-Ps from the water cores to isooctane. The relevant rigorous diffusion equations imply two fitting parameters, the radius of the water aggregates (r 0 ) and a transmission factor (h). Fixation of r 0 ) 3.6 nm for C AOT ) 0.1 M, w 0 ) 20, and T ) 294 K, as known from previous work, allows the quantitative derivation of the r 0 values for all other conditions. The water spheres appear to present some permeability to o-Ps, with a transmission factor h ) 0.12 nm -1 . The sphere radius increases smoothly with C AOT and w 0 and, more importantly, with T. The changes with w 0 give r 0 ) 0.181w 0 and 0.186w 0 nm at 294 and 298 K, respectively, and are in excellent agreement with previous proposals. The sum of the intensities, I tot ) I 3 + I 4 , is much lower than the o-Ps intensity in pure isooctane. In particular, at C AOT > 0.04 M, I tot appears very close to the value found for pure water. The possibility of a strong inhibition of Ps formation due to the micelles, as proposed in previous work, is ruled out because of the negligible electron or positron scavenging ability of alkyl sulfonates. It is thus concluded that Ps formation occurs primarily in the aqueous part of the micelles, the water aggregates representing efficient traps for the positrons while they are slowing down in the solutions. IntroductionPositronium (Ps), the bound state of a positron (e + ) with an electron (e -), has been used increasingly in recent decades as an efficient probe of the physical and chemical properties of matter. 1 The most commonly used positron annihilation technique (PAT) is lifetime spectroscopy (LS), which allows us to obtain both the lifetimes (τ i ) and relative abundances (or intensities, I i ) of the various positron species. Normally, in order of increasing lifetimes, these are singlet Ps (p-Ps, i ) 1), free positron (i ) 2), and triplet Ps (o-Ps, i ) 3). Because of its distinct long lifetime, the latter appears to be the most useful probe. The o-Ps decay occurs with the emission of two γ-rays through the pick-off process, i.e., the annihilation of the positron with one of the (bound) electrons of the surrounding medium. Information is obtained through two distinct, independent processes, Ps formation and annihilation, both of which depend on various characteristics of the systems under investigation. In liquids, Ps formation may occur on a very short time ...

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Section: Resultssupporting

confidence: 64%

Section: Resultsmentioning

confidence: 88%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Four-Component Analysis and Modeling of Positron Annihilation Lifetime Parameters in AOT/Water/Isooctane Microemulsions

Marques¹,

Miguel

Lima

et al. 1996

J. Phys. Chem.

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“…As shown in Figure 8, τ 3 decreases significantly with increasing salt concentration up to 22 wt % and then it remains approximately constant within the experimental error ((0.05 ns). As the Li + and ClO 4 -ions are unable to promote inhibition or quenching effects, 51 the observed decrease of the τ 3 values may be related to a decrease in the mean radius of the free-volume cavities of the amorphous phases, probably due to the coordination of the Li + ions with the solvating sites of the polymer, as observed for the PU(PEG/PPG)/LiClO 4 system. 19 The higher slope of the decrease in τ 3 is in the same concentration region in which T g1 shows a linear increase.…”

Section: Resultsmentioning

confidence: 81%

Study of Correlations between Microstructure and Conductivity in a Thermoplastic Polyurethane Electrolyte

Furtado

Silva²,

Machado³

et al. 1999

J. Phys. Chem. B

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Micro-Raman and positron annihilation lifetime spectroscopy (PALS) have been used to investigate the structure of a thermoplastic polyurethane/LiClO 4 solid flexible polymer electrolyte at room temperature. Correlation between the free volume and carrier concentration with ionic conductivity was observed. The polyurethane soft phase consisted of a poly(tetramethylene glycol-co-ethylene glycol) copolymer reinforced by condensation with hexamethyldiisocianate. The range of salt concentration between 5 and 35 wt %, which attained the beginning of phase segregation, was also studied by differential scanning calorimetry (DSC), which showed the presence of three thermal events; the soft-phase T g , a change in heat capacity suggested as the hard-phase T g , and a hard-phase ordering endotherm. The total ionic conductivity was found to be approximately 4 × 10 -6 S cm -1 at 23°C up to 27 wt % salt, whereas there were pronounced changes observed by the spectroscopic techniques. The PALS measurements indicated a decrease of 40% of the ratio (V f I 3 /(V f I 3 ) 0 ) between the free volume parameters probed by the positron particle. This ratio is proportional to the fractional free volume of the system. The micro-Raman results showed an increase of ionic aggregation, although the charge carrier concentration increased significantly in the range of compositions studied. The opposite effects of the microstructural changes and the maximum conductivity value, in the observed range of concentrations, are discussed.

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“…The spectral intensity associated with the o-Ps lifetime component is related to the volume fraction of these free volume cavities, if no Ps-quenching functional groups exist in the molecular structure, as is the case in the present study. [18] In recent years, PAS has found increasing interest and growing application in the studies of the local free (empty) volume cavities in polymeric materials. Such cavities play a crucial role in the general mechanical and rheological properties of polymers.…”

Section: Introductionmentioning

confidence: 99%

Physico‐Chemical Characterization of Nanofiltration Membranes

et al. 2007

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This study presents a methodology for an in-depth characterization of six representative commercial nanofiltration membranes. Laboratory-made polyethersulfone membranes are included for reference. Besides the physical characterization [molecular weight cut-off (MWCO), surface charge, roughness and hydrophobicity], the membranes are also studied for their chemical composition [attenuated total reflectance Fourier spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS)] and porosity [positron annihilation spectroscopy (PAS)]. The chemical characterization indicates that all membranes are composed of at least two different layers. The presence of an additional third layer is proved and studied for membranes with a polyamide top layer. PAS experiments, in combination with FIB (focused ion beam) images, show that these membranes also have a thinner and a less porous skin layer (upper part of the top layer). In the skin layer, two different pore sizes are observed for all commercial membranes: a pore size of 1.25-1.55 angstroms as well as a pore size of 3.20-3.95 angstroms (both depending on the membrane type). Thus, the pore size distribution in nanofiltration membranes is bimodal, in contrast to the generally accepted log-normal distribution. Although the pore sizes are rather similar for all commercial membranes, their pore volume fraction and hence their porosity differ significantly.

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Correlation between pulse radiolysis and positron annihilation techniques data

Cited by 51 publications

References 37 publications

Four-Component Analysis and Modeling of Positron Annihilation Lifetime Parameters in AOT/Water/Isooctane Microemulsions

Four-Component Analysis and Modeling of Positron Annihilation Lifetime Parameters in AOT/Water/Isooctane Microemulsions

Study of Correlations between Microstructure and Conductivity in a Thermoplastic Polyurethane Electrolyte

Physico‐Chemical Characterization of Nanofiltration Membranes

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