Influence of Polymer Crystallinity and Morphology on Positron Annihilation Characteristics

Dębowska, M.

doi:10.12693/aphyspola.110.559

Cited by 5 publications

(4 citation statements)

References 19 publications

(26 reference statements)

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“…The lifetimeo fC CN is relativelys hort compared with g-CNU and g-CNM. [18] This finding implies that the mobility of chargesi nC CN is fast because of existing crystal-line-amorphous interfaces,w hich agreesw ith the resultsf rom HRTEM and XRD. The results from PL, time-resolved PL, and photocurrent spectra confirm that the charge separation and transfer in g-CN can be promoted by increasing the crystallinity.…”

supporting

confidence: 81%

Modulating Crystallinity of Graphitic Carbon Nitride for Photocatalytic Oxidation of Alcohols

et al. 2017

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Exploiting efficient photocatalystsw ith strengtheneds tructure for solar-driven alcohol oxidation is of great significance. The photocatalytic performance of graphitic carbon nitrides can be considerably promoted by modulating its crystallinity.R esults confirmedt hat ah igh crystallinity accelerates the separation and transfer of photogenerated charge carriers, thus providing more free charges for photoredox reactions. More importantly, the high crystallinity facilitated the adsorption of benzyl alcohol and desorptiono fb enzaldehydea nd simultaneously lowered the energy barrierf or O 2 activation.A saresult,t he crystalline carbon nitride exhibited aroughlytwelvefold promotion with respectt ot he normalc arbon nitride. The remarkable enhancement of activity can be attributed to the synergistic effects of increased electron-hole separation and increased surface reactionk inetics. These findings will open up new opportunities to modulate the structure of polymers for aw ide variety of organic reactions.

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supporting

confidence: 81%

Modulating Crystallinity of Graphitic Carbon Nitride for Photocatalytic Oxidation of Alcohols

et al. 2017

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“…Figure 10 shows the sum ( I 2 + I 3 ) and crystallinity as a function of electron irradiation fluence. Figure 10 clearly shows that the maximum sum of I 2 + I 3 gives the minimum value of crystallinity as was discussed earlier for some semicrystalline polymers 28 …”

Section: Resultssupporting

confidence: 66%

Electron irradiation induced molecular changes in PMMA: A positron spectroscopy study

Awad

Alkureda

Abdel-Hady

et al. 2020

Polymers for Advanced Techs

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To examine the positron annihilation parameters with regard to microstructural changes, the positron annihilation lifetime spectroscopy and measurements of the Doppler broadening of annihilation radiation (DBAR) of electron‐irradiated poly(methyl methacrylate) were carried out at room temperature. Trapping rate equations were applied in terms of the positron bulk lifetime as well as the positron lifetime fitting results to investigate the molecular changes due to electron irradiation effects. It was found that the mean positron lifetime shows the same trend as the o‐Ps intensity. In disordered regions, the positronium trapping rate suggests that trapping of o‐Ps increases with increasing electron irradiation fluence until electron fluence reached 5.9 × 1013 electrons/cm2, after which it begins to decrease. The line shape S‐parameter was found to have similar behavior as the o‐Ps intensity, and suggests that poly(methyl methacrylate) undergoes chain scission, followed by cross‐linking, and eventually degradation, due to the electron radiation effects. The results of positron annihilation spectroscopy were verified by X‐ray results, mechanical, and electrical measurements.

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“…The annihilation of positrons in a polymer normally occurs via several pathways. One of the pathways, o-Ps pickoff annihilation, is often sensitive to polymer free volume element size and concentration, which are characterized by o-Ps lifetime and intensity, respectively. , PALS has been used to study the microstructure of various polymers, such as glassy and partially crystalline polymers, − thermally stable polymers, gas separation polymers, ,, and polymer hydrogels. ,− Moreover, free volume, as probed by PALS, correlates well with transport properties in polymeric materials as diverse as gas separation membranes ,,, and hydrated polymer hydrogels. , Desalination membrane materials have also been investigated using PALS. ,, On the basis of these studies, the positron annihilation technique can probe free volume, which is important in determining penetrant selectivity in reverse osmosis membranes …”

Section: Introductionmentioning

confidence: 99%

Effect of Free Volume on Water and Salt Transport Properties in Directly Copolymerized Disulfonated Poly(arylene ether sulfone) Random Copolymers

et al. 2011

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The influence of cation form and degree of sulfonation on free volume, as probed via positron annihilation lifetime spectroscopy (PALS), and water and salt transport properties was determined in a systematic series of directly copolymerized disulfonated poly(arylene ether sulfone) random copolymers. Polymer samples were studied in both the dry and hydrated states. PALS-based estimates of free volume in the dry polymers were compared with those estimated using density and the Bondi group contribution method, and PALS-based free volume data for hydrated polymers were correlated with water and salt transport properties. The transport properties depend strongly on free volume cavity size. Samples with larger free volume elements have higher water and salt solubility, diffusivity, and permeability and lower water/salt diffusivity and permeability selectivity. Sorption of water alters the characteristic free volume of the polymer matrix by two competing mechanisms: water molecules partially occupy the original free volume in the initially dry polymer, thereby reducing free volume cavity size, and water swells the polymer matrix therefore increasing the mean free volume size as a result of increased polymer chain plasticization. The importance of the second effect increases as water uptake and, thus, plasticization increases.

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Influence of Polymer Crystallinity and Morphology on Positron Annihilation Characteristics

Cited by 5 publications

References 19 publications

Modulating Crystallinity of Graphitic Carbon Nitride for Photocatalytic Oxidation of Alcohols

Modulating Crystallinity of Graphitic Carbon Nitride for Photocatalytic Oxidation of Alcohols

Electron irradiation induced molecular changes in PMMA: A positron spectroscopy study

Effect of Free Volume on Water and Salt Transport Properties in Directly Copolymerized Disulfonated Poly(arylene ether sulfone) Random Copolymers

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