Polyfluorene Thin Films Synthesized by a Novel Plasma Polymerization Method

The synthesis of polyfluorene (PF) thin films by simultaneously superposing a continuous and pulsed discharge and the characterizations of these samples are presented. The double discharge plasma system is constructed by superposing two discharges; namely, a low pressure dc glow one and a high current pulsed one. The fluorene monomer in powder form was vaporized in the system at argon plasma without any modification, at 0.5 mbar operating pressure. The structure of the thin films was investigated via XPS, UV–visible, FTIR, XRD and SEM. The FTIR and the UV–visible results revealed that the fluorene structure was retained at the produced samples. Semi-conducting behavior was established, and upon the iodine doping, the optical energy band gap (E _g ) dropped down from 3.7 to 2.4 eV. The morphology of the synthesized PF thin films was amorphous, with granular structures of different sizes depending on the location of the substrate.     

Global weak solutions to a ferrofluid flow model

We are concerned with the global solvability of the differential system introduced by Shliomis to describe the flow of a colloidal suspension of magnetized nanoparticles in a nonconducting liquid, under the action of an external magnetic field. The system is a combination of the Navier–Stokes equations, the magnetization equation, and the magnetostatic equations. We prove, by using a method of regularization, the existence of global‐in‐time weak solutions with finite energy to an initial boundary‐value problem and establish the long‐time behaviour of such solutions. The main difficulty is due to the singularity of the gradient magnetic force and the torque. Copyright © 2007 John Wiley & Sons, Ltd.     

Nonexponential relaxation of the metastable state of the spin-crossover system [Fe(L)2](ClO4)2.H2O [L = 2,6-Bis(pyrazol-1-ylmethyl)pyridine

The relaxation of the metastable state of the spin-crossover compound [Fe(L)(2)](ClO(4))(2).H(2)O, with L = 2,6-bis(pyrazol-1-ylmethyl)pyridine, populated by the LIESST (light induced excited spin state trapping) effect, has been investigated by magnetic measurements. The time dependence of the relaxation curve at several temperatures, starting from different initial states, is in the shape of stretched exponentials, and the thermal variation of the photostationary state under constant photoexcitation is progressive and reversible. These features are satisfactorily modeled by considering noninteracting two-level systems with a distribution of activation energies. A suggested origin for the distribution is the conformational flexibility of the nonplanar heterocyclic ligands. The effect of the intensity distribution during the LIESST process is also accounted for in a simple way.     

Theoretical study of laser light generation and color image formation: FA1:Cs+ and FA2:Li+ centers at the low coordination (100) and (110) surfaces of AgCl and AgBr

The F_A1:Cs⁺ and F_A2:Li⁺ color centers at the low coordination (100) and (110) surfaces of AgCl and AgBr play important roles in laser light generation and color image formation. Double‐well potentials at these surfaces are investigated by using ab initio calculations. Quantum clusters were embedded in the simulated Coulomb fields that closely approximate the Madelung fields of the host surfaces, and ions that are the nearest neighbors to the F_A ? defect site are allowed to relax to equilibrium. The calculated Stokes shifts suggest that laser light generation is sensitive to the simultaneous effects of the vibrational coupling mode, the impurity cation, the coordination number of the surface ion, the lattice anion, and the choice of the basis set centered on the anion vacancy. An attempt has been made to explain these effects in terms of Madelung potential, electron affinity, and optical–optical conversion efficiency. All relaxed excited states of the defect‐containing surfaces are deep below the lower edges of the conduction bands of the ground‐state defect‐free surfaces, suggesting that the F_A(I):Cs⁺ and F_A(II):Li⁺ centers are suitable laser defects. The dependence of orientational destruction, recording sensitivity, and exciton (energy) transfer on the empty cation; the coordination number of the surface ion; and the lattice anion is clarified. The Glasner–Tompkins empirical rule was generalized to include the impurity cation and the coordination number of the surface ion. As far as color image formation is concerned, the supersensitizer was found to increase the sensitizing capabilities of two primary dyes in the excited states by increasing the relative yield of quantum efficiency. The (110) surfaces of AgBr and AgCl were more sensitive than the corresponding (100) surfaces, and AgBr thin film was found to be more sensitive than that of AgCl. On the basis of quasi‐Fermi levels, the difference in the sensitizing capabilities between the examined dyes in the excited states is determined. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Dielectric properties of cleaned and monodisperse polystyrene latexes in microwaves

The dielectric behavior (, ) of three well-cleaned monodisperse polystyrene latexes having the same particle size and the same number of chemically-bound surface groups has been studied at a fixed microwave frequency (9.4 GHz), as a function of temperature and surface group (SO ₄ ^– , COO^–, OH).A large dielectric relaxation was observed in the sulfate-stabilized latex, which has the most polar surface end-group. The anomalous behavior in the thermal dependence of the hydroxyl and carboxyl-stabilized latexes (the OH latex being more pronounced than the COO^– latex) may originate from differences in the experimental conditions used for the preparation of such polymer colloids, or due to the presence of ionic species.On the basis of various dielectric models, the apparent volume fractions of the latexes were calculated. The amount of bound water around the latex particle was quantitatively correlated to the polarity of surface end-group (SO ₄ ^– > COO^– > OH). The differences between the calculated and actual values were not only a reflection of the thickness of vicinal water, but could also be indicative of the presence of oligomeric species in the suspension's medium (serum) of the latex. The permittivities of hydrated particle and of bound water were obtained with a non-linear iterative procedure.     

Complexes of iron(III) salen and saloph Schiff bases with bridging 2,4,6-<Emphasis Type="BoldItalic">tris</Emphasis>(2,5-dicarboxyphenylimino-4-formylphenoxy)-1,3,5-triazine and 2,4,6-<Emphasis Type="BoldItalic">tris</Emphasis>(4-carboxyphenylimino-4′-formylphenoxy)-1,3,5-triazine

Four new trinuclear Fe(III) complexes involving tetradenta Schiff bases N,N ¹ -bis(salicylidene) ethylenediamine-(salenH₂) or bis(salicylidene)-o-phenylenediamine-(salophH₂) with 2,4,6-tris(2,5-dicarboxyphenylimino-4-formylphenoxy)-1,3,5-triazine (DCPI-TRIPOD) or 2,4,6-tris(4-carboxyphenylimino-4′-formylphenoxy)-1,3,5-triazine (CPI-TRIPOD) have been synthesized and characterized by means of elemental analysis carrying out ¹H-n.m.r., i.r. spectroscopy, thermal analyses and magnetic susceptibility measurements. The complexes can also be characterized as high-spin distorted octahedral Fe^III bridged by carboxylic acids. The tricarboxylic acids play a role as bridges for weak antiferromagnetic intramolecular exchange.     

New external reagents for the simultaneous microdetermination of carbon,hydrogen and mercury

Non-conventional, extremely cheap and readily available materials, namely zinc plates, pumice granules or polystyrene foam cubes, have been utilized as new external mercury-retentive agents at room temperature for the simultaneous gravimetric microdetermination of mercury, carbon and hydrogen by the rapid straight empty-tube method of Korshun and Klimova. A standard Pregl absorption tube charged with the reagent is connected between the combustion tube and the water-absorption tube. Satisfactory results are obtained for carbon, hydrogen and mercury, and compare reasonably well with those found by using the traditional silver wool or gold sponge under similar conditions. Sulphur or halogen can also be determined simultaneously, as usual.     

Mössbauer study and molecular orbital calculations on some bimetallic derivatives of ferrocene and ferricinium

We have studied by absorption Mössbauer spectroscopy, some bridged derivatives of biferrocene, unoxidized (Fe^II– Fe^II) and mono-oxidized (Fe^II – Fe^III). The mixed-valence species exhibits a quasi-delocalized behavior at the Mössbauer timescale (～ 10^?8 s), with a splitting of the lines which is interpreted in terms of a partial valence trapping. This in turn reveals intramolecular properties at variance from those of the unbridged cation. SCC-Xα MO calculations have been performed; they correctly reproduce the measured quadruple splittings and provide evidence that the HOMO of the mixed-valence complex is of \(d_{xy} ,d_{x^2 - y^2 } \) type. Some consequences on the mixed-valence properties are discussed.     

Kinetics of anhydride formation in poly(acrylic acid) and its effect on the properties of a PAA-alumina composite

The kinetics of anhydride formation of poly(acrylic acid) (PAA) in porous PAA–alumina composites have been investigated by using a thermogravimetric technique (TGA). Three distinct reaction peaks at 200°C (I), 250°C (II), and 390°C (III) were identified in the dynamic TGA thermogram. These peaks were attributed to bound water removal (I), anhydride formation (II), and polymer degradation (III). The kinetics of the anhydride reaction were studied in a temperature range of 220–240°C and found to follow a second-order mechanism with an activation energy of approximately 38 kcal/mole. In addition, the bound water was found to inhibit the onset of anhydride formation. The degree of conversion to anhydride was correlated with the equilibrium swelling level attained by the composite in water.     

Solid-liquid equilibria and purity determination for binary n-alkane + naphthalene systems

Mixtures of heavy aromatics with high aliphatics are important in the formation of asphaltenes in the oil industry.This work reports binary solid-liquid equilibria for naphtalene + eicosane, +pentacosane, +hexatriacontane mixtures by differential scanning calorimetry. Results are compared with those from modified UNIFAC (Larsen and Gmehling versions) and ideal predictions. Finally, we determine the purity according to van’t Hoff equation. Results are in good agreement with values given by ultraviolet spectrophotometry.