Thermal behaviour of polyacrylamidoxime-copper chelates

The purpose of this work was to investigate the effect of several factors (anion type in the copper salt, pH and concentration of the salt solution) on the structure and thermo-oxidative degradation of the polyacrylamidoxime-copper chelates, by using elemental analysis, IR spectroscopy and dynamic thermogravimetry. The chelates containing copper ions as sulphate exhibit a better initial thermal stability than the polyacrylamidoxime fibre presumably due to the crosslinking generated by the intermolecular complexation of the ions; the removal of the sulphate anions takes place concomitantly with the second step of polymeric chain decomposition. The initial thermal decomposition of the chelates formed by copper ions as nitrate begins at lower temperatures as compared to the polyacrylamidoxime fibre, probably by the nitrate anion release, which partly overlaps the initial decomposition of the copper ion-crosslinked polymeric chains. Copper ions as either sulphate or nitrate catalyse the reactions involved in the main step of polyacrylamidoxime fibre decomposition; the higher the copper amount, the stronger the catalytic effect.     

Periodic unfolding and Robin problems in perforated domains

The periodic unfolding method was introduced in 2002 by D. Cioranescu et al. for the study of classical periodic homogenization. In this Note, we extend this method to perforated domains introducing also a boundary unfolding operator. As an application, we study the homogenization of some elliptic problems with Robin condition on the boundary of the holes. To cite this article: D. Cioranescu et al., C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

Mesomorphic behaviour and TSDC measurements of ortho-metallated palladium(II) and platinum(II) complexes with S,O-donor co-ligands

A series of ortho-metallated Pd and Pt complexes containing an imine ligand carrying three alkoxy chains and N-benzoylthiourea derivatives as co-ligands were prepared and their liquid crystalline properties investigated. Their structures were assigned based on elemental analysis, IR and ¹H NMR spectroscopy, whereas thermal properties were investigated by differential scanning calotimetry and polarising optical microscopy. All the compounds exhibit monotropic transitions involving nematic and smectic A phases, with the mesomorphic behaviour strongly related to the type of N-benzoylthiourea as well as the metal centre used. The thermally stimulated depolarisation current technique was employed to determine the conduction mechanism, phase transition temperature and the activation energies for one of the ortho-metallated Pd complexes.     

Study concerning the electrical resistivity of some liquid metals in ultrasonic field

The increasing of the electrical resistivity values for the overheated high-purity liquid aluminium in range 934 K to 1043 K and for aluminium-silicon eutectic alloy in range 850 K to 960 K, during high-energy ultrasonic field presence is reported. We used DC electrical resistivity measurements. The modification of electrical resistivity values in ultrasonic field due to electron-ion interaction processes and the limited current density in liquid metals is discussed. The effect of cavitation at the high temperature is debated.     

Synthesis of core‐shell structured carboxylated microparticles with a straightforward procedure and their evaluation as a polymer support

Poly(trimethylolpropane trimethacrylate) microspheres with a narrow size distribution were obtained by precipitation polymerization. They were subsequently modified by surface grafting with acrylic acid in a polar ethanol–water reaction medium, without stabilizer, yielding core‐shell particles with diameters in the micrometer range. The resulting polymeric material was characterized by SEM and potentiometric titration, FTIR spectroscopy, and thermal analysis. It was shown that the particle characteristics (size, size distribution, and functionality) obtained by this straightforward procedure can be controlled by modifying the synthesis parameters (monomer concentration, agitation rate, and temperature). The high functionality, the chemical and physico‐mechanical stability, as well as the possibility to control the performances of the resulting polymeric materials by synthesis allow its applications in various areas. Envisaging separation and catalysis domains, Cu(II), Cd(II), and Cr(III) uptake capacity from aqueous solutions was investigated under noncompetitive conditions as a function of synthesized particle functionality, time, and pH range. It was also found that the addition of the carboxylated microparticles to polyethylene stabilized with α‐tocopherol improved the thermo‐oxidative behaviour of the polymeric material. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5889–5898, 2005     

Effects of montmorillonite modification on optical properties of heterogeneous nematic liquid crystal - clay mineral nanocomposites

Investigations of montmorillonite (MMT) clay mineral modification effects on electro-optical properties of nanocomposites, based on the nematic liquid crystal 4-pentyl-4'-cyanobiphenyl (5CB) and MMT have been carried out. Only the composite with MMT modified by an organic surface-active substance, dioctadecyldimethylammonium chloride, has been shown to manifest electro-optical memory effect and contrast. A polar dopant (acetone), added to the mixture, significantly increases composite homogeneity. Results of IR spectroscopy measurements lead to the conclusion, that there is a mutual influence of components on each other in organoclay systems, which appears as an alignment of near-surface layers of both the organic and inorganic components of the composite. Due to such interactions these systems show electro-optical contrast and memory effect. A composite with organophobic Na-MMT does not show these electro-optical properties, due to the absence of component interactions, as shown by IR spectroscopic data.     

Electrical resistivity study of some lead-borate glasses

We present the results of electrical resistivity measurements performed on 20Fe₂O₃80[3B₂O₃(1?x)PbOxA_uO_v] glasses, with AuOv=K₂O, Ca, As₂O₃ and GeO₂. For a given temperature the electrical conductivity is linearly dependent on the fraction of ferrous ions. The experimental data are well described by using a model involving small polarons.     

Stable bundles on hypercomplex surfaces

A hypercomplex manifold is a manifold equipped with three complex structures I, J, K satisfying the quaternionic relations. Let M be a 4-dimensional compact smooth manifold equipped with a hypercomplex structure, and E be a vector bundle on M. We show that the moduli space of anti-self-dual connections on E is also hypercomplex, and admits a strong HKT metric. We also study manifolds with (4,4)-supersymmetry, that is, Riemannian manifolds equipped with a pair of strong HKT-structures that have opposite torsion. In the language of Hitchin’s and Gualtieri’s generalized complex geometry, (4,4)-manifolds are called “generalized hyperkähler manifolds”. We show that the moduli space of anti-self-dual connections on M is a (4,4)-manifold if M is equipped with a (4,4)-structure.     

Functional polymers based on acrylamide crosslinked copolymers

Crosslinked copolymers of acrylamide were obtained by the aqueous suspension polymerization method. Divinylbenzene and N,N-methylene-bis-acrylamide were used as crosslinking agents. Ethylacrylate was used as a third comonomer. The real acrylamide content in the crosslinked copolymers was calculated taking into account the found nitrogen content after the removal of the soluble fractions. The water uptake in dependence on the copolymer structure gave information on the hydrophilicity of these copolymers. Hofmann degradation of the amide groups led to copolymers containing vinylamine functional groups, which were characterized by IR spectroscopy and by anion exchange capacity. Carboxylic groups were generated by the alkaline hydrolysis of the ester groups.