Study of electrical,mechanical, and nanoscale free‐volume properties of NBR and EPDM rubber reinforced by bentonite or kaolin

The effect of Na bentonite, Ca bentonite, and kaolin fillers on the macrostructure and microstructure of acrylonitrile butadiene rubber, ethylene propylene diene rubber, and their blend (50/50) was studied through electrical and mechanical measurements, as well as with positron annihilation lifetime spectroscopy. The real part of permittivity (ε′), dielectric loss (ε″), and the crosslinking density were found to increase with increasing filler content. The increase of crosslinking density of the blend with increasing amount of fillers reflects a decrease in the equilibrium swelling up to 21.50 wt % compared with that of the unfilled blends. The mechanical investigation showed pronounced increase in the tensile strength, and in elongation at break with the addition of up to 21.50 wt % of filler. In addition, comparing between different fillers showed that the reinforcing effect of Na bentonite is more effective than Ca bentonite and kaolin but the physico‐mechanical of Ca bentonite is less than that for kaolin. The positron annihilation lifetime measurements revealed that the free‐volume properties were strongly affected by the amount and type of filler, in particular, the free‐volume fraction was dramatically decreased with increasing filler content. Furthermore, correlations were made between the free‐volume parameters and both electrical and mechanical properties. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1825–1838, 2009     

Synthesis,characterization, and electroluminescence properties of poly(fluorenevinylene benzobisthiazoles)

A series of vinylene‐linked copolymers based on electron‐deficient benzobisthiazole and electron‐rich fluorene moieties were synthesized via Horner–Wadsworth–Emmons polymerization. Three different polymers P1 , P2 , and P3 , were prepared bearing octyl, 3,7‐dimethyloctyl, and 2‐(2‐ethoxy)ethoxyethyl side chains, respectively. The polymers all possessed moderate molecular weights, good solubility in aprotic organic solvents, and high fluorescence quantum efficiencies in dilute solutions. P2 , which bore branched 3,7‐dimethyloctyl side chains, exhibited better solubility than the other polymers, but also exhibited the lowest thermal decomposition temperature of all polymers. Overall, the impact of the side chains on the polymers optical properties in solution was negligible as all three polymers gave similar absorption and emission spectra in both solution and film. Guest‐host light‐emitting diodes using dilute blends of the polymers in a poly(N‐vinylcarbazole) host gave blue‐green emission with P2 exhibiting the highest luminous efficiency, 0.61 Cd/A at ～500 nm. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

An Efficient Scheme for Stochastic Finite Element Solutions

The Polynomial Chaos expansion in Stochastic Finite Element Methods increases the size of the resulting linear systems dramatically. In iterative scheme which takes the underlying statistics into account is suggested for the efficient numerical solution. Additionally, an approach for the solution of von Mises stresses from the Polynomial Chaos representation of the displacement field is outlined. (© 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation and measurement of AES depth profiles; a case study of the C/Ta/C/Si system

A multilayer sample (C (23.3 nm)/Ta (26.5 nm)/C (22.7 nm)/Si substrate) was submitted to AES depth profiling by Ar⁺ ions of energy 1 keV and angles of incidence of 72°, 78°, and 82°. The shapes of the as-measured depth profiles were strongly different emphasizing that the ion-bombardment conditions strongly affects the shapes of measured depth profiles. We simulated the depth profile measured at an angle of incidence of 72° by calculating the backscattering factor, applying attenuation lengths available in the literature, and simulating the ion-bombardment-induced specimen alteration with a TRIDYN simulation and a trial and error method. The good agreement between the calculated and measured depth profiles justified the method applied.     

Improved analytical formulae for correcting elastic-scattering effects in X-ray photoelectron spectroscopy

We present new predictive formulae for the correction parameters Q_x and β_eff that are used to account for the effects of elastic scattering in quantitative X-ray photoelectron spectroscopy. These formulae were derived from an analysis of published calculations of Q_x and β_eff from extensive Monte Carlo simulations for a group of elemental solids. Two formulae are given for each parameter. One formula is a function of the single-scattering albedo and the photoelectron emission angle, and is useful for emission angles between 0° and 80°. The other formula is a function only of the single-scattering albedo and is useful for emission angles between 0° and 50°. The single-scattering albedo is in turn a simple function of two material parameters, the inelastic mean free path and the transport mean free path. The latter parameters can be determined readily from available predictive formulae for any material or from databases. The root-mean-square and mean deviations of the Monte Carlo values of Q_x and β_eff from those found with the new formulae are comparable to or smaller than those found with formulae published by Seah and Gilmore.     

Relationships between electron inelastic mean free paths, effective attenuation lengths, and mean escape depths

The terms inelastic mean free path (IMFP), effective attenuation length (EAL), and mean escape depth (MED) are frequently used to specify the surface sensitivity of Auger-electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). These terms are different conceptually because of the effects of elastic-electron scattering, and generally have different numerical values for a specified material and electron energy. In addition, values of the EAL and MED depend on the instrumental configuration. We give an historical overview of efforts to measure EALs by the overlayer method and of work to investigate elastic-scattering effects in AES and XPS. We then apply an analytical formalism developed from a solution of the kinetic Boltzmann equation within the transport approximation to demonstrate the relationships between the IMFP, EAL, and MED for selected elemental solids and for common measurement conditions. Examples are given to show the magnitude of elastic-scattering effects on MED values for angle-resolved XPS and AES. If XPS or AES data are acquired for emission angles between zero and 60°, the ratio of the MED to that found with elastic scattering neglected is approximately constant (to within 10%), and this ratio can be used to determine an average value for the EAL. This EAL value can then be used to establish the depth scale in the data analysis. Finally, we show ratios of the EAL to the IMFP for XPS from the Au 4s subshell with Mg K X-rays as a function of emission angle and depth; this ratio has a weak dependence on emission angle from zero to 40° but a more pronounced dependence for larger emission angles.     

EPES sampling depth paradox for overlayer/substrate system

An unexpected interface effect for the sampling depth of elastic peak electron spectroscopy (EPES) in applications to the overlayer/substrate system has been found. The sampling depths expressed as an information depth (ID) for Au/Ni and Rh/Al systems and selected energies in the range 200–10,000 eV were obtained from Monte Carlo (MC) simulations for typical for EPES cylindrical mirror analyser (CMA) configuration. It turned out that deep minimum in the ID dependence on the interface depth can exist. For example, for Rh/Al system at the energy of 2000 eV the ID can be smaller by a factor of two than the ID for the system elements. This effect can be explained in terms of the differential cross sections.     

Synthesis and Antitumor Evaluation of Some New Fused and Binary Pyridines

Syntheses of some new heterocyclic compounds containing pyridone, thioxopyridine, halogenated‐pyridine‐carbonitriles, pyrazolopyridine, and pyridine derivatives were achieved. Besides, a modified synthetic method for the synthesis of 2‐chloro‐4,6‐dimethyl‐nicotinonitrile ( 3 ) through the reaction of acetylacetone and malononitrile as starting materials was implemented. The reaction of 2‐chloronicotinonitrile 3 with substituted amines to 2‐aminonicotinonitrile were also investigated. Fused or binary pyridines were tested for cytotoxicity against well‐known established model Ehrlich ascites cells in vitro. Compound 13 exhibited a high antitumor activity compared with 5‐fluorouracil.     

Surface excitation correction of the inelastic mean free path in selected conducting polymers

In earlier works, the inelastic mean free path (IMFP) of electrons was determined by elastic peak electron spectroscopy (EPES) using Ni and Ag reference standard samples, but fully neglecting surface excitation. Surface excitation that is characterized by the surface excitation parameter (SEP), and may affect considerably the elastic peak for the sample and the reference material. The SEP parameters of selected conducting polymers (polythiophenes, polyaniline and polyethylene) were determined by EPES using Si and Ge reference samples. Experiments were made with a hemispherical analyzer of energy resolution 100-200 meV in the E = 0.2-2.0 keV energy range. The composition of the sample surfaces was determined by in situ XPS, their surface roughness by AFM. The experimental SEP parameter data of eight polymer samples were determined by our new procedure, using the formulae of Chen and Werner et al. in the E = 0.2-2.0 keV energy range. The trial and error procedure is based on the best approach between the experimental and calculated IMFPs, corrected on surface excitation. The improvement in the SEP correction appears in the difference between the corrected and Monte Carlo calculated IMFPs, assuming Gries and Tanuma et al. IMFPs for polymers and standard, respectively. The term describing the improvement by SEP resulted in 50-72% (good correction for five polymers) 24% (poor correction for one polymer), 1-6% (no correction for two polymers). The 100% correction was not achieved, indicating that the difference between experimental and calculated IMFP cannot be entirely explained by surface excitation. Using the SEP data of Si and Ge reference samples based on Chen's and Werner's material parameter values resulted in similar SEP corrections for the polymer samples.