Colloidal stability of aqueous nanofibrillated cellulose dispersions

Cellulose nanofibrils constitute an attractive raw material for carbon-neutral, biodegradable, nanostructured materials. Aqueous suspensions of these nanofibrils are stabilized by electrostatic repulsion arising from deprotonated carboxyl groups at the fibril surface. In the present work, a new model is developed for predicting colloidal stability by considering deprotonation and electrostatic screening. This model predicts the fibril-fibril interaction potential at a given pH in a given ionic strength environment. Experiments support the model predictions that aggregation is induced by decreasing the pH, thus reducing the surface charge, or by increasing the salt concentration. It is shown that the primary mechanism for aggregation upon the addition of salt is the surface charge reduction through specific interactions of counterions with the deprotonated carboxyl groups, and the screening effect of the salt is of secondary importance.     

Mössbauer analysis of Fe−N austenites

Analysis of transmission Mössbauer spectra for high nitrogen Fe?N austenites is done in terms of five iron environments dealing with first and second nearest neighbour shells. The similar analysis for Fe?C austenites which displays only three iron environments led to the conclusion that carbon atoms are ordered whereas nitrogen atoms are more randomly distributed.     

Liouville Theorems for a General Class of Nonlocal Operators

In this paper, we study the equation \(\mathcal {L} u=0\) in \(\mathbb {R}^{N}\), where \(\mathcal {L}\) belongs to a general class of nonlocal linear operators which may be anisotropic and nonsymmetric. We classify distributional solutions of this equation, thereby extending and generalizing recent Liouville type theorems in the case where \(\mathcal {L}= (-{\Delta })^{s}\), s ∈ (0, 1) is the classical fractional Laplacian.     

Heck reaction with an alkenylidenecyclopropane: the formation of arylallylidenecyclopropanes

The palladium-tetraphosphine catalyzed arylation of an alkylidenecyclopropane gives a simple and direct access to 1-aryl-2-methyl-1-(2,2,3,3-tetramethylcyclopropylidene)propenes. This reaction tolerates several functional groups on the aryl bromides. Even heteroaryl bromides have been used successfully. This reaction probably proceeds via a classical oxidative addition of the aryl bromide to palladium, insertion of the CCMe₂ bond in the Ar-Pd bond followed by β-elimination to give the dienes.     

Luminescence Properties of Poly(3-Methoxythiophene)—Bithiophene Composite Oligomers

The electronic absorption and fluorescence spectra of electrosynthesized poly(3-methoxythiophene)— bithiophene (PMOT-BT) composite oligomers were studied in organic solution (DMSO) and/or in the solid state on ITO plates. Different spectral properties (absorption and fluorescence maximum wavelengths, fluorescence quantum yields, etc.) were found to depend on the bithiophene initial concentration used during electrosynthesis and, subsequently, on the film composition and oligomer chain length.     

Crystal structure and ionic conductivity of the soft solid crystal: isoquinoline<Subscript>3</Subscript>•(LiCl)<Subscript>2</Subscript>

A soft solid crystal composed of isoquinoline (IQ) and LiCl was prepared based on the concept of Pearson’s hard-soft acid-base (HSAB) theory. Single-crystal X-ray diffraction best described the isoquinoline₃?(LiCl)₂ as consisting of molecular Li₄Cl₄(isoquinoline)₆ units, where the LiCl cluster is an array of edge-fused Li₂Cl₂ rhombs. Electrochemical impedance measurements on pressed pellets showed that conductivity occurs mainly through the bulk via a hopping mechanism, with a calculated activation energy of E_a = 67 kJ/mol. The high value of the activation energy was due to Li₄Cl₄ clusters that were well separated by intervening IQ ligands in the crystal structure, requiring large hops for ions to migrate through the lattice.     

Detection of Cadmium and Copper Cations Using Amorphous Nitrogenated Carbon Thin Film Electrodes

Nitrogenous amorphous carbon (a‐CN_x) thin films were deposited by radio‐frequency cathodic magnetron sputtering (13.56 MHz) on polished and etched titanium disks. While these films are cheaper to prepare than commonly reported carbon‐based electrodes, the usable electrochemical window in aqueous solution is within the same range and spans from ?1.5 to +1.8 V vs. SCE. The electrochemical reactivity was tested using the ferri‐ferrocyanide redox couple as a function of the thin films preparation parameters. The obtained electrochemical properties allow the use of these a‐CN_x thin films for stripping electroanalysis of cations in water, minimizing potential solvent reactivity. Cadmium and copper were used to test these detection abilities. Better analytical properties (notably sensitivity and linearity) were obtained as compared to a commercial boron doped diamond electrode. Preliminary competition/interaction experiments for these two cations were performed.