Crosslinked PVA/SSA proton exchange membranes: correlation between physiochemical properties and free volume determined by positron annihilation spectroscopy

Gomaa, Mahmoud M.; Hugenschmidt, Christoph; Dickmann, Marcel; Abdel-Hady, E.E.; Mohamed, Hashim; Abdel-Hamed, M.O.

doi:10.1039/c8cp05301d

Cited by 142 publications

(114 citation statements)

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“…This is due mainly to the loss of moisture adhesion and removal of water molecules from the polymer matrix, with the pristine PVA incurring the greatest loss of water molecules. The second stage of weight loss for the pristine PVA is then observed from 250 to 300 °C, which is attributable to the breakage of C-C and C-O bonds, as the thermal energy is then able to degrade the linear chains of the pristine PVA (Gomaa et al 2018). The ester linkages and additional hydrogen bonds present within the cross-linked PVA structures are gradually degraded in the range of 160 °C.…”

Section: Thermal Stabilitymentioning

confidence: 99%

Fabrication of PVA polymer films with improved antibacterial activity by fine-tuning via organic acids for food packaging applications

et al. 2020

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In this study, organic acids were used as cross-linker with polyvinyl alcohol (PVA) films prepared by a solution-casting method for food packing applications. The effect of incorporating three different organic acids, i.e., malic acid (MA), tartaric acid (TA), and lactic acid (LA), on the physicochemical and biological properties of PVA was explored in detail. The crystalline phase, optical absorption, and functional groups were examined via UV-Vis and Fourier transform infrared spectroscopy. Thermal, microstructural, and surface investigations were conducted by thermogravimetric analysis and scanning electron microscopy, and the antibacterial activity was evaluated. The surface topography and roughness were found to have a strong effect on the bactericidal properties of the films, as confirmed by atomic force microscopy. Among the considered films, PVA/LA exhibited the highest bacterial inhibition, which was largely due to its capacity to modify the local pH and alter the permeability of the microbial layer by disrupting bacteria-substrate interaction. In general, the composite film was found to have attractive properties and can be considered as a food packaging material with low environmental impact based on polyvinyl alcohol.

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Section: Thermal Stabilitymentioning

confidence: 99%

Fabrication of PVA polymer films with improved antibacterial activity by fine-tuning via organic acids for food packaging applications

et al. 2020

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“…Gomaa et al 25,26 prepared cross-linked polyvinyl alcohol/ sulfosuccinic acid (PVA/SSA) as a proton exchange membrane for fuel cell applications. They found that the ionic conductivity and the thermal stability of the crosslinked membranes improved by increasing the concentration of SSA.…”

Section: Introductionmentioning

confidence: 99%

Study of the nanostructure of free volume and ionic conductivity of polyvinyl alcohol doped with NaI

Hmamm

Zedan

Hamed

et al. 2020

Polymers for Advanced Techs

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Positron annihilation lifetime (PAL), AC conductivity, and impedance spectroscopy have been applied for the investigation of polyvinyl alcohol (PVA) doped with different concentrations of NaI in the range from zero to 25 wt%. Wide‐angle x‐ray diffraction measurements reveal that the addition of NaI to the PVA structure leads to a decrease in the crystallinity of the sample. The free volume size obtained from PAL measurements increases with the increase of the NaI concentration on PVA. NaI acts as an inhibitor of positronium formation on the doped polymer with inhibition constant of 0.028 (Mol%)−1. The ionic conductivity of the investigated sample was found to be correlated with the free volume size, which indicates the major role of free volume in the conduction mechanism. The AC conductivity of the prepared samples is measured at room temperature in the frequency range from 50 Hz to 5 MHz. The calculated values of frequency exponent s indicate the hopping mechanism in ionic conductivity. Impedance spectroscopy of PVA doped with different concentrations of NaI was studied. The appeared semi‐circle, in the Nyquist plot, denotes the bulk influence of PVA with different concentrations of NaI. This has been attributed to the parallel connection of bulk resistance and bulk capacitance. Also, the semi‐circle radius of Cole‐Cole plots was found to decrease with the increase of the concentration ratio (wt%) of NaI. So, the increase of the conductivity of PVA with the increase of NaI contents has been investigated.

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“…However, several studies reported a similar trend of lower resistivity at higher temperatures and related this decrease to the re-agglomeration of carbon black aggregates to be responsible for the observed decline in the resistivity [62,63]. Additionally, the increase of the free volume size inside the polymers due to the temperature rise has been shown to increase the conductivity, which is another possible explanation for the observed decrease in resistivity [64].…”

Section: Temperature Dependence Of Volume Resistivitymentioning

confidence: 76%

Volume Resistivity of Viton Polymer under Thermal Aging

2021

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This study examines the influence of various electrical parameters on the volume resistivity of the Viton fluoroelastomer. The transient current, the temperature dependence of volume resistivity, the voltage dependence of resistivity, and the surface morphology of Viton insulators are investigated for new and aged specimens. An accelerated aging process has been employed in order to simulate the natural aging of insulators in service. A detailed comparison between the new and aged samples is presented. The transient effect, which is a challenge to the resistivity measurement of insulators, has been investigated. The first 60 s of the resistivity measurement test showed a significant influence from the transient effect and should be excluded from the data. The volume resistivity of both new and aged samples decreased when the temperature increased. However, the resistivity of the aged sample was lower than the new one at all tested temperatures. When the temperature increased from 35 to 190 °C, resistivity decreased from 4.77 × 1010 to 6.99 × 108 Ω-cm for the new sample and from 2.6 × 1010 to 6.68 × 108 Ω-cm for the aged sample under 500 V. Additionally, the results from this study showed that the volume resistivity is inversely proportional to the applied voltage. Finally, scanning electron microscope (SEM) micrographs/images allowed us to closely examine the surface morphology of new and aged Viton samples. The surface of aged samples has been recognized with higher surface roughness and more significant surface cracks leading to poor performance under high voltage applications.

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Crosslinked PVA/SSA proton exchange membranes: correlation between physiochemical properties and free volume determined by positron annihilation spectroscopy

Abstract: At low humidity (<30 RH%), water molecules begin to fill the intermolecular spaces in the membrane. At high humidity (80 RH%) the membrane swells; the free volume size increases.

Cited by 142 publications

References 50 publications

Fabrication of PVA polymer films with improved antibacterial activity by fine-tuning via organic acids for food packaging applications

Fabrication of PVA polymer films with improved antibacterial activity by fine-tuning via organic acids for food packaging applications

Study of the nanostructure of free volume and ionic conductivity of polyvinyl alcohol doped with NaI

Volume Resistivity of Viton Polymer under Thermal Aging

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