Mohamoud Mohamoud - Academia.edu (original) (raw)

Papers by Mohamoud Mohamoud

ECS Meeting Abstracts

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In this work, complex but not complicated spherical trigonometry functions were used to determine... more In this work, complex but not complicated spherical trigonometry functions were used to determine the Islamic prayer times. To the best of our knowledge, it is the first time that a mathematical modelling of the relative shadow height of objects at zenith time has been visually presented for each Julian day of the year in great detail; this is a requirement step for the end and beginning of Zuhr and Asr prayer times, respectively. For practical and proof-of-concept purpose – albeit its applicability to all locations without exception, the prayer times for the capital cities of the under-investigated region of East African countries i.e. Kenya, Somalia, Ethiopia and Djibouti were chosen as case studies for mathematical calculations and data interpretation in addition to Mecca as a benchmark. All the mathematical equations needed for the determination of the beginning for each prayer time were thoroughly reviewed. For data analysis, the widely available MS Excel programme was utilized...

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... Karl S. Ryder and Andy P. Abbott ... 6 Electrodeposition of Metals (Chapter 4), TJS Schuber... more ... Karl S. Ryder and Andy P. Abbott ... 6 Electrodeposition of Metals (Chapter 4), TJS Schubert, SZ El Abedin, AP Abbott, KJ McKenzie, KS Ryder and F. Endres, in Electrodeposition in Ionic Liquids, Edited by F. Endres, AP Abbott and DR Macfarlane, Wiley-VCH Weinheim, 2008 ...

Plastics Engineering, Nov 1, 2008

Journal of Solid State Electrochemistry, Jul 23, 2013

Electrochimica Acta, 2014

ABSTRACT We report significant improvement, though unexpected contrary to intuition, of the redox... more ABSTRACT We report significant improvement, though unexpected contrary to intuition, of the redox behaviour and electrochemical pseudo-capacitance of polyaniline (PAn) conducting polymer composited with non-conducting poly(vinyl alcohol) (PVA). Redox and film composition characterizations were carried out using a combination of in situ electrochemical and nanogravimentric techniques. Film structural changes due to the presence of PVA in the matrix of PAn have been studied with FT-IR and XRD as well as thermal analysis techniques such as TGA and DSC. The increase in PAn/PVA film redox responses compared to pure PAn film was observed to be a factor of ca. 2 while electrochemical capacitance enhancement was obtained to be ca. 40% increase (ca. 130 F g−1 for PAn/PVA composite film compared to ca. 94 F g−1 for PAn). These drastic improvements of composite film's redox behaviour were attributed to the increase in film chain-chain interactions due to the presence of multiple hydrogen bonding created by the introduction of PVA chain segments in the bulk of PAn film and thus enhancing the rate of film redox conversions. Redox enhancement was also associated to the increase in composite film's ion doping capacity.

Journal of Solid State Electrochemistry, 2013

ABSTRACT The deposition and properties under electrochemical potential control of composite films... more ABSTRACT The deposition and properties under electrochemical potential control of composite films of polyaniline and single walled carbon nanotubes were studied using high frequency acoustic wave measurements at quartz crystal resonators. Acoustic admittance spectra were used to provide shear moduli for the growing films as functions of thickness and dopant anion (sulfate, nitrate or perchlorate). The electrochemical and viscoelastic data were compared with those obtained in a parallel set of experiments in the absence of carbon nanotubes. The presence of carbon nanotubes in the deposition solution enhances the rate of polyaniline deposition by a factor of 3–5, according to the dopant. In all media, the shear modulus components increased with film thickness and in any given medium both the storage and the loss moduli were greater in the presence of carbon nanotubes. Since SEM images do not reveal the presence of the carbon nanotubes directly, they are deduced to interact sufficiently strongly with the polymer as to become fully encapsulated. A mean field model is adapted to provide predictive capability at a simplistic level for composite film viscoelastic properties in terms of the mechanical properties of the constituents. When applied to the experimental data, it suggests that the level of carbon nanotube incorporation is modest, despite its significant effect on film deposition and properties.

Journal of Solid State Electrochemistry, 2007

Electrochemical quartz crystal microbalance (EQCM) and crystal admittance measurements were used ... more Electrochemical quartz crystal microbalance (EQCM) and crystal admittance measurements were used to study the potentiodynamic electrodeposition of polyaniline films. Variations in peak admittance provided the distinction between acoustically thin and acoustically thick films. In the former instance, the Sauerbrey equation was used to interpret the EQCM frequency shift in gravimetric terms. In the latter case, admittance spectra were interpreted viscoelastically to yield shear storage and loss moduli. Variations in storage modulus with potential (within a given deposition cycle) and with number of deposition cycles (at a given potential) were small, covering the range 1.1-1.6× 10 7 dyn cm −2 . Variations in loss modulus were much more dramatic, increasing from very low levels typical of a simple fluid to values similar to the storage modulus. More subtle variations of both components within a single potential cycle were highlighted using a novel differential format. This revealed two peaks, correlating with the first film redox process and with further film oxidation/polymerization.

Electrochimica Acta, 2008

ABSTRACT Crystal admittance measurements during potentiodynamic electrodeposition from aqueous HC... more ABSTRACT Crystal admittance measurements during potentiodynamic electrodeposition from aqueous HCl of polyaniline films on a thickness shear mode resonator show the phenomenon of film resonance. This special situation arises when the combination of materials properties (film shear modulus and density) and sample nature (film thickness) is such that the acoustic phase shift across the film, φ=π/2 radians. Admittance spectra in the acoustically thick (but pre-film resonance) region were fitted to a standard Butterworth van Dyke (BvD) electrical equivalent circuit (with series L, C, and R elements) to yield film storage and loss shear moduli. From these values, it was possible to calculate φ of the growing film and thereby track the onset of film resonance. As φ approached π/2 radians, the admittance peak rapidly shifted to higher frequencies and changed dramatically in amplitude. An electrical equivalent circuit with parallel L, C, and R elements was used to model film resonance data; this simplified model ignores the contribution of the bathing electrolyte. Agreement of film shear moduli from both models, and of resonant film thickness from the parallel element equivalent circuit model and coulometric extrapolation of pre-resonant responses, supports the basic tenets of the film resonance model. At film resonance, the cyclic voltammetric response changed dramatically; it is speculated that this is a consequence of the unusual polymer dynamics at film resonance.

Electrochimica Acta, 2006

We describe the application of a new model for the visualization of mobile species (ion and solve... more We describe the application of a new model for the visualization of mobile species (ion and solvent) transfers accompanying redox switching of electroactive films. The system studied was polyaniline, for which the mobile species population changes were determined from redox-driven film mass changes using a thickness shear mode acoustic wave resonator. Acoustic admittance data were used to establish conditions under which the resonator frequency response could be interpreted gravimetrically. Charge and frequency changes accompanying the first redox transition of polyaniline films exposed to aqueous perchloric acid were then used to determine the film's ion and solvent populations. The data are best described by a mechanism in which the early stages of film oxidation are associated with proton transfer (exit) and the latter stages with perchlorate transfer (entry) to satisfy electroneutrality; solvent enters throughout film oxidation and exits throughout film reduction. The alternative of a single ion satisfying electroneutrality throughout would require the rather less likely situation of a non-monotonic solvent flux. Application of the model's diagnostic criteria indicates that the film solvent population is in equilibrium on the timescale of slow scan voltammetry, but shows thermodynamic non-idealities. Hysteresis in the film ion population signals failure of the redox state to maintain equilibrium with the applied potential.

Electrochimica Acta, 2007

ABSTRACT Acoustic admittance measurements at thickness shear mode resonators were used to determi... more ABSTRACT Acoustic admittance measurements at thickness shear mode resonators were used to determine shear moduli for polyaniline films during their potentiodynamic electrodeposition and subsequent redox cycling in aqueous background electrolyte. Data were acquired for films doped with perchlorate, sulphate or chloride anion. For all media, film shear moduli increased progressively with film thickness, from values consistent with a diffuse fluid-like layer to values typical of a viscoelastic material. At any given thickness, both the storage and loss moduli were largest in perchlorate medium; values in chloride and sulphate media were similar to each other, but smaller than in perchlorate. These measures of polymer dynamics are consistent with a previous classification of polyaniline film behaviour, in which perchlorate-doped films are viewed as compact while chloride- and sulphate-doped films are viewed as more open. In monomer-free background electrolyte solution, both film shear modulus components for all anions increased modestly upon film oxidation. Despite some hysteresis on the timescale of slow scan voltammetry, these variations were chemically reversible. Based on measurements involving deposition from chloride medium and transfer to sulphate medium, film shear moduli respond promptly to changes in dopant identity; this is consistent with rapid redox-driven exchange of anions with the bathing electrolyte.

Electroanalysis, 2005

... A. Robert Hillman,a* Mohamoud A. Mohamoud,a Stanley Bruckensteinb a University of Leicester, ... more ... A. Robert Hillman,a* Mohamoud A. Mohamoud,a Stanley Bruckensteinb a University of Leicester, Department of Chemistry, University Road, LE1 7RH, UK b Department of Chemistry, University at Buffalo/SUNY, Buffalo, NY 14260-3000, USA *e-mail: arh7@le.ac.uk ...

Chinese Science Bulletin, 2004

ABSTRACT Polymer solutions have very important applications in the enhanced oil recovery due to t... more ABSTRACT Polymer solutions have very important applications in the enhanced oil recovery due to their unique viscoelastic properties increasing microscale displacement efficiency. In this paper, the viscoelastic properties of partially hydrolyzed polyacrylamide (HPAM) solution have been investigated. Results show that the viscoelastic properties of HPAM increase with HPAM concentration increasing, and decrease with the increase of sodium dodecyl sulfate (SDS). Meanwhile, adding NaCl can destroy the viscoelastic properties.

Chemical Communications, 2009

The electrochemical quartz crystal microbalance was used to determine redox-driven ion transfers ... more The electrochemical quartz crystal microbalance was used to determine redox-driven ion transfers accompanying p-doping of polypyrrole (PPy) films in the choline chloride-based deep eutectic ionic liquid ethaline; electroneutrality maintenance is gravimetrically dominated by choline cation transfer and this requires the presence within the undoped film of ionic liquid, when this finite reservoir of choline is exhausted there is a shift to chloride transfer.

Analytical Chemistry, 2011

Comprehensive exploration of the viscoelastic properties of polyaniline films exposed to aqueous ... more Comprehensive exploration of the viscoelastic properties of polyaniline films exposed to aqueous perchloric acid has been made as a function of applied potential (E), temperature (T), and mechanical oscillation frequency (f = ω/2π) using high-frequency acoustic wave resonators. The outcomes are expressed in terms of storage and loss shear modulus signatures, G&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;(E, T, ω) and G″(E, T, ω). Surprisingly, these are barely sensitive to potential, through which both polymer charge and solvation are manipulated, and only modestly sensitive to temperature. In contrast, the response to timescale is dramatic. Using the principle of time-temperature superposition, G&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; and G″ at different temperatures and frequencies (time scales) can each be placed on master relaxation curves. Models developed for mechanical properties of bulk polymers at low frequency were applied to these thin film responses at high frequency. These include the Williams-Landel-Ferry model, the activation model, and the Rouse-Zimm model based, respectively, on concepts of free volume, thermal activation, and relaxation. Each of the models could be applied with physically reasonable outcomes in terms of the relevant parameters (thermal expansion coefficient, glass transition temperature, and activation enthalpy). G&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; and G″ values are correlated with solvent content. The enthalpy change for solvent entry is small, positive and relatively independent of polymer charge state, all of which contrast sharply with the behavior of thiophene-based conducting polymers in organic solvents.

Journal of Taibah University for Science, 2014

In this report, we investigate the electrochemical capacitance and redox behaviour of a stand-alo... more In this report, we investigate the electrochemical capacitance and redox behaviour of a stand-alone polyaniline-poly(vinyl alcohol) composite film cast on an insulating substrate (normal printer paper) and compared it with an electrochemically synthesized composite film deposited on a gold electrode. The stand-alone composite film showed timescale-dependent, wide range charging-discharging redox cycling and high electrochemical capacitance in potentiodynamic electrochemical experiments carried out in 1 M HCl solution.