Abdalla Obeidat

Nucleation rates of water and heavy water using equations of state.

The original formula of Gibbs for the reversible work of critical nucleus formation is evaluated in three approximate ways for ordinary and heavy water. The least approximate way employs an equation of state to evaluate the pressure difference between the new and old phases. This form of the theory yields a temperature dependence for the nucleation rate close to that observed experimentally. This is a substantial improvement over the most commonly used (and most approximate) form of classical theory.

Evolution of a current in a resistor

The current in a simple electric circuit consisting of a resistor and a power supply is studied under the assumption that the current starts from zero and reaches its maximum value. It suggests that an evolution process of a current occurs approximating the circuit temporarily to an R-L circuit. The current equation is solved analytically using Mittag-Leffler function. The equation was also solved numerically. Results supported the assumed behavior of current to evolve from zero to its saturation value.

Two-Dimensional Texture of Intrinsic Conductive Poly(styrene-co-maleanilic Acid) Grafted with Polyaniline: Formation and Conductivity

Intrinsically conducting polyaniline is grafted onto a preformed poly(styrene-co-maleanilic acid) copolymer backbone via chemical oxidative coupling of aniline in acidified chloroform/water emulsion. The structure and textural morphology of the grafted poly(S-co-MA-g-PANI) are examined by different spectroscopic, thermal, powder X-ray diffraction and scanning electron microscopic techniques. The d.c. electrical conductivity of the grafted emeraldine base of the obtained materials displays a d.c. conductivity of the order of 10−7 – 10−9 Scm−1, which is ∼2 orders of magnitude greater than that of the reported PANI-EB homopolymer. This enhancement in d.c. conductivity is explained in terms of microstructure-electronic conductivity relationship.

The structure of D2O-nonane nanodroplets

We study the internal structure of nanometer-sized D2O-nonane aerosol droplets formed in supersonic nozzle expansions using a variety of experimental techniques including small angle X-ray scattering (SAXS). By fitting the SAXS spectra to a wide range of droplet structure models, we find that the experimental results are inconsistent with mixed droplets that form aqueous core-organic shell structures, but are quite consistent with spherically asymmetric lens-on-sphere structures. The structure that agrees best with the SAXS data and Fourier transform infra-red spectroscopy measurements is that of a nonane lens on a sphere of D2O with a contact angle in the range of 40°-120°.

Nucleation Rates of Methanol Using the SAFT-0 Equation of State†

Classical and nonclassical calculations of nucleation rates are presented for methanol, an associating vapor system. The calculations use an equation of state (EOS) that accounts for the effects of molecular association based on the statistical association fluid theory (SAFT). Two forms of classical nucleation theory (CNT) were studied: a Gibbsian form known as the P-form and the standard or S-form. CNT P-form calculations and nonclassical gradient theory (GT) calculations were made using the SAFT-0 EOS. Calculated rates were compared to the experimental rates of Strey, et al. [J. Chem. Phys. 1986, 84, 2325-2335]. Very little difference was found between the two forms of CNT for either the temperature (T) or supersaturation (S) dependence of the rates. Nucleation rates based on GT showed improved T and S dependence compared to CNT. The GT rates were also improved by factors of 100-1000 compared to CNT. Despite these improvements, GT does not describe the reported T and S dependence of the nucleation rates. To explore this further, the GT and experimental rates were analyzed using Hales scaled model [J. Chem. Phys. 2005, 122, 204 509]. This analysis reveals an inconsistency between the predictions of GT, which scale relatively well, and the experimental data, which do not scale. It also shows that the measured rate data have an anomalous T and S dependence. A likely source of this anomaly is the inadequate thermodynamic data base for small cluster properties that was used originally to correct the raw rate data for the effects of association.

The validity of the potential model in predicting the structural, dynamical, thermodynamic properties of the unary and binary mixture of water-alcohol: Methanol-water case

Two intermolecular potential models of methanol (TraPPE-UA and OPLS-AA) have been used in order to examine their validity in reproducing the selected structural, dynamical, and thermodynamic properties in the unary and binary systems. These two models are combined with two water models (SPC/E and TIP4P). The temperature dependence of density, surface tension, diffusion and structural properties for the unary system has been computed over specific range of temperatures (200-300K). The very good performance of the TraPPE-UA potential model in predicting surface tension, diffusion, structure, and density of the unary system led us to examine its accuracy and performance in its aqueous solution. In the binary system the same properties were examined, using different mole fractions of methanol. The TraPPE-UA model combined with TIP4P-water shows a very good agreement with the experimental results for density and surface tension properties; whereas the OPLS-AA combined with SPCE-water shows a very agreement with experimental results regarding the diffusion coefficients. Two different approaches have been used in calculating the diffusion coefficient in the mixture, namely the Einstein equation (EE) and Green-Kubo (GK) method. Our results show the advantageous of applying GK over EE in reproducing the experimental results and in saving computer time.Two intermolecular potential models of methanol (TraPPE-UA and OPLS-AA) have been used in order to examine their validity in reproducing the selected structural, dynamical, and thermodynamic properties in the unary and binary systems. These two models are combined with two water models (SPC/E and TIP4P). The temperature dependence of density, surface tension, diffusion and structural properties for the unary system has been computed over specific range of temperatures (200-300K). The very good performance of the TraPPE-UA potential model in predicting surface tension, diffusion, structure, and density of the unary system led us to examine its accuracy and performance in its aqueous solution. In the binary system the same properties were examined, using different mole fractions of methanol. The TraPPE-UA model combined with TIP4P-water shows a very good agreement with the experimental results for density and surface tension properties; whereas the OPLS-AA combined with SPCE-water shows a very agreement wit...

Sensitive detection schemes for small variations in the damping coefficient based on the Duffing-Holmes oscillator with a potential application in magnetic sensing

In this work we proposed two detection schemes based on the non-linear properties of the Duffing-Holmes oscillator for the detection of small variations in the damping coefficient. Theoretically, variations in the damping coefficient up to 0.001% with the possibility to be pushed further can be detected based on our model. A potential on-off magnetic sensor suitable for biomedical applications is suggested by implementing these two schemes with Giant Magnetoresistance based magnetic sensors.In this work we proposed two detection schemes based on the non-linear properties of the Duffing-Holmes oscillator for the detection of small variations in the damping coefficient. Theoretically, variations in the damping coefficient up to 0.001% with the possibility to be pushed further can be detected based on our model. A potential on-off magnetic sensor suitable for biomedical applications is suggested by implementing these two schemes with Giant Magnetoresistance based magnetic sensors.

The structure of D[subscript 2]O-nonane nanodroplets

We study the internal structure of nanometer-sized D2O-nonane aerosol droplets formed in supersonic nozzle expansions using a variety of experimental techniques including small angle X-ray scattering (SAXS). By fitting the SAXS spectra to a wide range of droplet structure models, we find that the experimental results are inconsistent with mixed droplets that form aqueous core-organic shell structures, but are quite consistent with spherically asymmetric lens-on-sphere structures. The structure that agrees best with the SAXS data and Fourier transform infra-red spectroscopy measurements is that of a nonane lens on a sphere of D2O with a contact angle in the range of 40°-120°.

The structure of D 2 O-nonane nanodroplets

We study the internal structure of nanometer-sized D2O-nonane aerosol droplets formed in supersonic nozzle expansions using a variety of experimental techniques including small angle X-ray scattering (SAXS). By fitting the SAXS spectra to a wide range of droplet structure models, we find that the experimental results are inconsistent with mixed droplets that form aqueous core-organic shell structures, but are quite consistent with spherically asymmetric lens-on-sphere structures. The structure that agrees best with the SAXS data and Fourier transform infra-red spectroscopy measurements is that of a nonane lens on a sphere of D2O with a contact angle in the range of 40°-120°.

Free energy of formation of small clusters using the BAR method and MD simulations

Accurate free energy difference calculations based on molecular dynamics (MD) simulations are still a computational challenge. In this study, the free energy differences between successive cluster sizes of SPC/E-water are calculated using the Bennett acceptance ratio (BAR) method at three temperatures, T = 220K, 240K, and 260K. The simulation results show that the free energy differences of the small clusters scale nicely with the inverse of TcT-1, using the appropriate critical temperature, Tc, of SPC/E-water of 625 K.