Free-volume hole relaxation in molecularly oriented glassy polymers

Xia, Zhiyong; Trexler, Morgana M.; Wu, Fei; Jean, Y. C.; Horn, J. David Van

doi:10.1103/physreve.89.022603

Cited by 14 publications

(10 citation statements)

References 62 publications

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“…The observed o ‐Ps pick‐off lifetime has been correlated with the size of free volume holes, and the corresponding intensity ( I 3 ) may be correlated with an apparent free volume fraction (ffv) from positron annihilation data . The voids are assumed spherical for the basis of the present analysis, as described before . A modified Tao‐Eldrup model, a robust semi‐empirical equation for free volume calculation, is applied here by fitting measured o ‐Ps lifetimes (τ 3 ) in a spherical potential well with established sizes of radius, R:

τ_{3} = 0.5 \times {[1 - \frac{R}{R + Δ R} + \frac{1}{2 π} \sin (\frac{2 italicπR}{R + Δ R})]}^{- 1}

where τ 3 and R, are in units of ns and Å, respectively, and ΔR was calibrated to be 1.656 Å .…”

Section: Methodsmentioning

confidence: 99%

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Positron annihilation lifetime spectroscopy study of polyvinylpyrrolidone‐added polyvinylidene fluoride membranes: Investigation of free volume and permeation relationships

Eren

Guney

et al. 2020

Journal of Polymer Science

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Polyvinylidene fluoride (PVDF) membranes were prepared via the phase inversion method from casting solutions containing PVDF, dimethylformamide (DMF), and polyvinylpyrrolidone (PVP) as pore former. PVP was used in the casting solution in a range of 0–5 wt % and extracted. The effect on membranes of using PVP in the casting process was analyzed by X‐ray diffraction, differential scanning calorimetry, scanning electron microscopy, viscosity, and water permeability techniques. With an increase of PVP from 0 to 5 wt %, the PVDF casting solution viscosities increased from 858 to 1148 cP; the resulting PVDF membrane thickness increased; and the crystallinity of PVDF membranes decreased from 40.0 to 33.3%, which indicates that the addition of PVP inhibits the degree of crystallization in the PVDF membranes. SEM results revealed the shape and size of macropores in the membranes; these macropores changed after PVP addition to the casting solutions. The impact of structural changes on free‐volume properties was evaluated using positron annihilation lifetime spectroscopy (PALS) studies. PALS analysis indicated no effect on the average radius (~3.4 Å) of membrane free‐volume holes from the addition of PVP to the casting solution. However, the percentage of o‐Ps pick‐off annihilation intensity, I3, increased from 1.7 to 5.1% with increased PVP content. Further, increasing the PVP content from 0.5 to 5% resulted in an increased final pure water permeability flux. For instance, the 210 min flux for a 14% PVDF + 0.5% PVP membrane was found to be 3.3 times greater than a control membrane having the same PVDF concentration. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020, 58, 589–598

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τ_{3} = 0.5 \times {[1 - \frac{R}{R + Δ R} + \frac{1}{2 π} \sin (\frac{2 italicπR}{R + Δ R})]}^{- 1}

where τ 3 and R, are in units of ns and Å, respectively, and ΔR was calibrated to be 1.656 Å .…”

Section: Methodsmentioning

confidence: 99%

“…Recently, correlation to void volume size has been extended to include the 3γ process from o ‐Ps and modified for hole sizes between 1 and 100 nm, corresponding to observed lifetimes longer than 10 ns …”

Section: Methodsmentioning

confidence: 99%

Positron annihilation lifetime spectroscopy study of polyvinylpyrrolidone‐added polyvinylidene fluoride membranes: Investigation of free volume and permeation relationships

Eren

Guney

et al. 2020

Journal of Polymer Science

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“…where ΔR = 0.166 nm is the thickness of electron layer at the wall of free volume hole [ 24 – 26 ]. The spherical free volume hole size was calculated by means of simple relation: …”

Section: Methodsmentioning

confidence: 99%

Nanoscale Observation of Dehydration Process in PHEMA Hydrogel Structure

Chamerski

Korzekwa²,

Filipecki

et al. 2017

Nanoscale Res Lett

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One of the most important field of interest in respect to hydrogel materials is their capability to water storage. The problem mentioned above plays an important role regarding to diffusion of fluid media containing nanoparticles, what is very useful in biomedical applications, such as artificial polymeric implants, drug delivery systems or tissue engineering.In presented work, dehydration process in hydrogels used in ophthalmology as intraocular lenses was observed. Before measurements studied materials were immersed in deionized water and saline solution to obtain equilibrium swelling state. Studies of the dehydration process were carried out by use of gravimetric analysis, Fourier-Transform Infrared and Positron Annihilation Lifetime Spectroscopy. Obtained results revealed changes in hydrogen bonding structure and free volume holes induced by saline solution ingredients.

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“…Positron spectrometric measurements were taken using a conventional fast-fast coincidence method with events compiled with a multichannel analyzer as previously described [17][18][19]. The time resolution of the spectrometer was < 300 ps, measured in a 100 ns window using a 60 Co source with 22 Na energy settings [20].…”

Section: Methodsmentioning

confidence: 99%

Positron Annihilation Lifetime Analysis of Left- and Right-Handed Alanine Single Crystals

Eren

et al. 2017

Acta Phys. Pol. A

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Studies of the interaction of polarized light or particles (including electrons, e − , or positrons, e + ) with asymmetric forms of matter has been of interest to scientists since the discovery of chirality and the subsequent development of particle physics. Researchers have been interested in e + interactions with chiral molecules for decades, but with mixed and indecisive results. After reviewing the field, we speculated that the e + or positronium (Ps) might interact differently with chiral pairs of large single crystals, i.e., the left-handed or right-handed asymmetric forms of the crystals -and subsequently observed significant differences in "free positron" annihilation and intensities in the evaluation of left-handed or right-handed quartz single crystals. This result may be understood to be a "particle stereorecognition" phenomenon. To extend this line of inquiry we crystallized mm scale L-or D-alanine crystals and performed positron annihilation lifetime spectroscopy measurements using a 22 Na positron source. Alanine crystals were obtained via slow evaporation of water in a Dewar, or from water/acetone solvent in a temperature-controlled environment. These methods resulted in small (≈ 0.5 cm/side) or large (≥ 1.0 cm/side) crystals, respectively. While some intensity (I2) results from left-handed and right-handed crystals varied in positron annihilation lifetime spectroscopy analysis, the errors associated with the measurements do not indicate a stereorecognition of alanine via positron interactions.

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Free-volume hole relaxation in molecularly oriented glassy polymers

Cited by 14 publications

References 62 publications

Positron annihilation lifetime spectroscopy study of polyvinylpyrrolidone‐added polyvinylidene fluoride membranes: Investigation of free volume and permeation relationships

Positron annihilation lifetime spectroscopy study of polyvinylpyrrolidone‐added polyvinylidene fluoride membranes: Investigation of free volume and permeation relationships

Nanoscale Observation of Dehydration Process in PHEMA Hydrogel Structure

Positron Annihilation Lifetime Analysis of Left- and Right-Handed Alanine Single Crystals

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