Prof. Hamdy F. M. Mohamed (original) (raw)

Papers by Prof. Hamdy F. M. Mohamed

Radiation Physics and Chemistry

Polymers

Polymer electrolyte membrane (PEM) fuel cells have the potential to reduce our energy consumption... more Polymer electrolyte membrane (PEM) fuel cells have the potential to reduce our energy consumption, pollutant emissions, and dependence on fossil fuels. To achieve a wide range of commercial PEMs, many efforts have been made to create novel polymer-based materials that can transport protons under anhydrous conditions. In this study, cross-linked poly(vinyl) alcohol (PVA)/poly(ethylene) glycol (PEG) membranes with varying alumina (Al2O3) content were synthesized using the solvent solution method. Wide-angle X-ray diffraction (XRD), water uptake, ion exchange capacity (IEC), and proton conductivity were then used to characterize the membranes. XRD results showed that the concentration of Al2O3 affected the degree of crystallinity of the membranes, with 0.7 wt.% Al2O3 providing the lowest crystallinity. Water uptake was discovered to be dependent not only on the Al2O3 group concentration (SSA content) but also on SSA, which influenced the hole volume size in the membranes. The ionic con...

Journal of Membrane Science, 2010

Free volume, O 2 permeability, and uniaxial compression storage modulus of biphenol-based sulfona... more Free volume, O 2 permeability, and uniaxial compression storage modulus of biphenol-based sulfonated poly(arylene ether sulfone) (BPSH) with an ion exchange capacity (IEC) of 1.60 mequiv./g were studied as a function of relative humidity at room temperature. The free volume hole size was quantified using the positron annihilation lifetime (PAL) technique, whereas the uniaxial compression storage modulus was measured by dynamic nanoindentation. Favorable formation of positronium (Ps) due to the antiinhibition effect of-SO 2-allowed for the application of the PAL technique to the study of free volume in BPSH. It was found that as the polymer is hydrated the free volume hole size (V FV,Ps) and O 2 permeability (P O 2) first decrease and then increase. A semi-logarithmic plot of P O 2 versus 1/V FV,Ps for BPSH at different relative humidities showed a good correlation similar to that for different polymers such as polystyrene and polycarbonate in the dry state. Tendency of P O 2 deviating from the correlation in highly hydrated BPSH suggests an effect of polymer softening on O 2 permeation in addition to the dominant effect of the free volume.

Journal of Polymer Research, 2017

Free volume properties, size and distribution, in the bisphenol-a based polycarbonate (PC) sheets... more Free volume properties, size and distribution, in the bisphenol-a based polycarbonate (PC) sheets were investigated as a function of the treatment duration by liquid acetone using the positron annihilation lifetime (PAL) spectroscopy. Along with increasing the PC treatment duration, the free volume sizes decreased and the holes-distribution broadened, which in turns led to the polymer crystallization induction. From the PAL and WAXD data, it has been confirmed that the crystallization capability of the amorphous PC tremendously enhanced, with a rapid increase of the PC crystallinity along with increasing the treatment duration by liquid acetone. These findings were further confirmed by the surface chemistry and topography characterization techniques which revealed the formation of crystalline structure after liquid acetone treatment. The solvent-induced crystallization of PC sheets promoted restrictions to the infrared induced molecular vibrations the surface functional groups which...

Polymers for Advanced Technologies, 2021

The Egyptian Journal of Chemistry, 2021

The adsorption of H2 in dehydrated and hydrated Materials of Institute Lavoisier (MIL-101) was in... more The adsorption of H2 in dehydrated and hydrated Materials of Institute Lavoisier (MIL-101) was investigated theoretically. The effect of terminal water molecules on adsorption as one of the more vital MIL-n trivalent chromium-based porous carboxylates in metal-organic frameworks application in the renewable energy field was also theoretically studied. The MIL-101 structures were optimized for geometry and energy minimization was performed. The calculations were carried out using density functional theory approach with B3LYP functional and mixed basis set of Lanl2DZ and 6-31G(d, p) for Cr and light atoms (C, H, O, F), respectively, as implemented in the Gaussian 09 program package. The spin and atomic charges distribution on the Cr metal atoms, adsorbate, and water molecules are calculated using natural bond orbital (NBO). The density of states (DOS) for the clusters was obtained using Gaussian smearing of Kohn–Sham orbital energies. The natural bond orbital (NBO) for molecular orbit...

Positron annihilation lifetime spectra were measured for polyvinylalcohol (PVA) doped with CuC12 ... more Positron annihilation lifetime spectra were measured for polyvinylalcohol (PVA) doped with CuC12 (0.5 to 5.0 wt%) at temperature range from room temperature to 160 ~ For a fresh pure PVA (without annealing) "t" 3 below Tg was larger in the heating runs than in the cooling runs, but above Tr "r 3 was the same for both runs. The larger r 3 values in the heating run were considered to be due to the existence of strain brought forth in the process of preparation. For annealed pure PVA z3 was the same for the heating and the cooling runs and Tg was shifted to lower temperature, 88 and 80 ~ for fresh and annealed samples, respectively. This shift was attributed to loss of H-bonded water in the annealed pure PVA by heating above 100 ~ Both ~3 and "r 3 were decreased by the added CuC12, being interpreted as the result of inhibition and quenching, respectively. The results show that both the inhibition coefficient otand the quenching rate constant k were smaller than the ...

Energy and Environment Research, 2018

Gasification is one of the most important solutions for plastic waste management. We researched t... more Gasification is one of the most important solutions for plastic waste management. We researched the conversion of plastic waste to fuel using sustainable material (Nano Clay) modified with Nano transition metals (TiO2, MnO, and ZnO). This was processed in a fix bed reactor design. After studying the reaction mechanism of the gasification process, we evaluated the optimize (reactor temperature, reaction time and feeding ratio of the modified catalyst) on the gasification process with its application for the modified catalyst on the degradation of polyethylene high density(PEHD), other waste plastic to fuel (CH4, H2, and other light component gasses). This method can be used as an important resource for renewable energy (like generating electricity and clean fuel), rather than waste for landfills and the incineration process which is the main source of CO2 emissions.

Polymers for Advanced Technologies

Journal of Polymer Research

In the present study, the effect of electric field on thermally treated Nafion 112 was investigat... more In the present study, the effect of electric field on thermally treated Nafion 112 was investigated successfully. The electrically modified Nafion membranes were examined using various techniques such as Fourier transform infrared (FTIR), water uptake, wide-angle x-ray diffraction (WAXD), proton conductivity, thermogravimetric analysis (TGA), tensile test, and positron annihilation lifetime (PAL) spectroscopy. The FTIR patterns show that the chemical structure of the Nafion 112 is unchanged with the electric field. The electric field decreases the degree of crystallinity as deduced from WAXD. Furthermore, the hole volume size deduced from PAL measurement increases with increasing the electric field strengths. As a result of the electric field effect on the thermally treated Nafion 112 membrane, the electrochemical properties were enhanced. The proton conductivity increases from 1.0 × 10–3 to 2.1 × 10–3 S/m. The water uptake increases from 7.4 to 15.5% with increasing the electric field strength up to 80 MV/m and then it reaches a plateau. It was also found that the mechanical and thermal properties of thermally treated Nafion 112 were enhanced because of the electric field effect. The hole volume size was increased from 0.136 to 0.160 nm3 as a function of the electric field. The results from different techniques were correlated successfully. The results were presented and discussed accordingly on a theoretical basis and compared to literature review data.

Egyptian Journal of Physics

Advances in Polymer Technology

Acta Physica Polonica A

Humidity control and water management in polymer electrolyte membranes for fuel cells are still o... more Humidity control and water management in polymer electrolyte membranes for fuel cells are still of high importance to improve the fuel cells' efficiencies. In this study, poly (vinyl alcohol) (PVA)was crosslinked using 15 wt% sulfosuccinic acid (SSA) by a solution casting method and additionally thermally crosslinked at 100 • C. Positron annihilation lifetime spectroscopy was used to study the mean free volume size and the distribution at different humidity. A slight decrease in the free volume was found up to a relative humidity of 30% whereas it increases strongly for a relative humidity of more than 30%. The volume of the voids duplicates from 0.036 to 0.078 nm 3 by changing the relative humidity from 30 to 80%. Thermogravimetric analyzer was used to determine the thermal stability of the membrane. From thermogravimetric analyzer data, it was found that the PVA with 15 wt% SSA membrane are chemically stable up to 200 • C.

Materials Science Forum, 2001

All rights reserved. No part of contents of this paper may be reproduced or transmitted in any fo... more All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 66.249.66.172-09/05/11,18:10:55) ... Positron Annihilation - ICPA-12 doi:10.4028/www. ...

Journal of Radioanalytical and Nuclear Chemistry Articles, 1996

Positron annihilation lifetimes were measured for several polymers in the atmosphere of high pres... more Positron annihilation lifetimes were measured for several polymers in the atmosphere of high pressure CO 2 gas. At low CO 2 pressured both r 3 and 13 decreased due t ~ the Langmuir-type sorption, and at higher pressures their values recovered because the Henry-type sorption takes over. The amount of sorbed CO 2 and dilation of the bulk volume were measured simultaneously, and the free volume fraction was determined at each CO 2 pressure. The free volume fraction became smaller (for polyimide and polycarbonate) or slightly larger (for polyethylene) with the progress of sorption. However, the size of the o-Ps hole estimated from the "r 3 value increased regardless of the change of the free volume fraction. It appears that o-Ps is selectively looking at larger holes or expanding the holes in which it is accommodated. For polycarbonate, which remains to be glassy even at the largest CO 2 smption attained in the experiment, the o-Ps hole size became larger than that before sorption. This implies that, even if the polymer is glassy as bulk, the sorption site is strongly prone to molecular displacement by the pressure of the penetrating Ps. Cautious consideration is evoked about directly correlating the o-Ps lifetime and intensity with the free volume in general.

Journal of Physical Chemistry B, 2009

The positron annihilation lifetime has been applied to study the effect of atmosphere (air and ox... more The positron annihilation lifetime has been applied to study the effect of atmosphere (air and oxygen gas) on A-type zeolite (MS-4A). The measurements were performed at 1 atm of oxygen gas and at 1 atm of air media at room temperature. The lifetime spectra were analyzed using two methods: 1) average results of the ortho-positronium (o-Ps) lifetime and its intensity obtained by PATFIT program and 2) o-Ps lifetime and hole volume distributions given by Bayes' theorem and the maximum entropy principle (MELT program). The results showed that the o-Ps lifetime components have small values when the sample was in oxygen gas medium compared with those in air medium and vacuum. This indicated that both the inhibition and quenching effects of the oPs parameters due to oxygen gas are taking place in MS-4A.

Yanbu Journal of Engineering and Science