A Shortcut Application of a Flory‐Like Model to Asphaltene Precipitation

A model, previously developed to determine the asphaltene precipitation onset, considered that asphaltene separation is ruled by the solvent quality of the surrounding media. Here, it is shown that it is equivalent to Flory‐Huggins model, when it is hypothesized that the asphaltene concentration is always in the instability range. With this, the controversy on the use of a concentration‐dependent model to describe a phenomenon that is practically independent of concentration is by‐passed. Moreover, improvements of the model are presented, together with sensitivity analysis with respect to its parameters. Two field case applications are reported, showing that the model gives a reasonable fit.     

Poly(phenylene oxide) copolymer anion exchange membranes

Poly(phenylene oxide) block and random copolymers are synthesized by oxidative polymerization of 2,6-dimethylphenol and 2,6-diphenylphenol for potential alkaline exchange membrane application. The copolymers are functionalized on the methyl substituted repeat units through a two-step process to produce pendent quaternary ammonium cationic groups. The amount of quaternary ammonium cations and the ion exchange capacity are quantified through titration measurements. Ionic conductivity of the copolymer membranes is measured by electrochemical impedance spectroscopy. Block copolymers show increased bromide conductivity at higher ion exchange capacities compared with the random copolymer analogs. The bromide conductivity for a block copolymer film with an ion exchange capacity of 1.27 mequiv/g reaches 26 mS/cm at 90 °C and 95% relative humidity. The hydroxide conductivity for the same film was measured to be 84 mS/cm at 80 °C and 95% relative humidity. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1770–1778, 2013     

Nanoassemblies with light‐responsive size and density from linear flexible polyelectrolytes

This study presents electrostatically self‐assembled nanoparticles from linear flexible polyelectrolytes (poly(diallyldimethylammonium chloride or quarternized poly(4‐vinylpyridine)) and an ionic photo‐isomerizable azo dye (Acid Yellow 38) that can change their size upon UV‐light irradiation. Assemblies with narrow size distribution are stable in aqueous solution. For samples with under‐stoichiometric dye load, UV‐light exposure triggers a size decrease, e.g. from a hydrodynamic radius of R_h = 94 nm to R_h = 62 nm for an Ay38‐PDADMAC sample with a charge ratio of l_charge = 0.7. Size changes are caused by trans‐cis isomerization of the dye, accompanied by a change in hydrophilicity, binding enthalpy and entropy. Assemblies are characterized by static and dynamic light scattering, atomic force microscopy, UV–vis spectroscopy and isothermal titration calorimetry. Zeta potential measurements give insight into the electrostatic stabilization and size‐control of the ionic nano‐assemblies, revealing a master curve of effective surface charge density versus hydrodynamic radius. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys., 2013     

Comment on “Density functional theory study of 1,2‐dioxetanone decomposition in condensed phase”

In the preceding paper results are presented, which are in serious conflict with state‐of‐the‐art ab initio method. Based on these new results the authors propose a new explanation of the reason for the preferential production of a phosphorescent state. Here we show that these controversial results are flawed, since the model use exclude biradical electron structures. © 2012 Wiley Periodicals, Inc.     

DFT study of the effect of substituents on the absorption and emission spectra of Indigo

ABSTRACT: BACKGROUND: Theoretical analyses of the indigo dye molecule and its derivatives with Chlorine (Cl), Sulfur (S), Selenium (Se) and Bromine (Br) substituents, as well as an analysis of the Hemi-Indigo molecule, were performed using the Gaussian 03 software package. RESULTS: Calculations were performed based on the framework of density functional theory (DFT) with the Becke 3- parameter-Lee-Yang-Parr (B3LYP) functional, where the 6-31 G(d,p) basis set was employed. The configuration interaction singles (CIS) method with the same basis set was employed for the analysis of excited states and for the acquisition of the emission spectra. CONCLUSIONS: The presented absorption and emission spectra were affected by the substitution position. When a hydrogen atom of the molecule was substituted by Cl or Br, practically no change in the absorbed and emitted energies relative to those of the indigo molecule were observed; however, when N was substituted by S or Se, the absorbed and emitted energies increased.     

An experimental investigation of the pressure and concentration dependence of muonic Coulomb capture and cascade in gases

Muonic Coulomb capture ratios and x-ray intensity patterns in four binary mixtures of the gases N₂, Ne, Ar, Kr, and Xe have been measured at three atomic ratios. An influence of the concentration has been established. The Lyman series intensity patterns of pure N₂, Ne, Ar, Kr, and Xe were measured at pressures between 0.4 and 51 bar and found to depend on the pressure. Possible explanations are discussed.     

Nonvanishing theorems for L-functions of modular forms and their derivatives

Inventiones mathematicae -