Synthesis and properties of novel donor–acceptor copolymers based on thiophene and squaraine moieties

Two novel donor–acceptor copolymers were synthesized by Sonogashira cross-coupling of alkyl/alkoxy thiophene and dibromo-substituted squaraine moieties. The structures and properties of these polymers were characterized using FT–IR, NMR, UV–Vis, gel permeation chromatography, and cyclic voltammetry. Both copolymers are readily soluble in common organic solvents. The polymer films exhibit broad absorption in the wavelength range from 300 to 1000 nm with the maximum peaks over 750 nm. Electrochemical studies reveal that the band gaps of the polymers range from 1.05 to 1.36 eV. Compared to the alkyl thiophene, the alkoxy thiophene units can effectively lower the band gap and result in significant red-shift absorption spectrum of the resulted polymer. The strong overlap of the solar spectrum and the extremely low band gaps of the polymers suggest that they may be promising candidates for solar cells.     

Synthesis and characterization of thiophene-based donor–acceptor type polyimide and polyazomethines for optical limiting applications

In this communication we describe the design and synthesis of four new conjugated polymers (P1–P4) based on 3,4-ditetradecyloxythiophene. The required diamine monomer was prepared by a unique catalyst-free reduction process using hydrazine hydrate. The structures of the intermediates and polymers were established by FTIR, ¹H NMR spectroscopy. Molecular weights of polymers were determined by gel permeation chromatographic (GPC) method. Their electrochemical properties were investigated by cyclic voltammetry and linear optical properties were determined by UV–Visible absorption and fluorescence emission spectroscopic techniques. Further, their nonlinear optical properties were evaluated by Z-scan technique using Nd:YAG laser. These polymers showed strong optical limiting behavior with two-photon absorption (2PA) coefficients of the order of 10^?10 m/W, which are comparable to that of good optical limiting materials reported in the literature. Also, it has been observed that the optical nonlinearity enhanced with the increase in donor–acceptor strength of the polymer backbone.     

Synthesis,characterization and third-order nonlinear optical properties of novel hyperbranched donor–acceptor polyfluorenes based on 1,3,6,8-tertsubstituted carbazole core

Two novel hyperbranched donor–acceptor polyfluorenes based on 1,3,6,8-tertsubstituted carbazole core (4BrCzP1 and 4BrCzP2) were synthesized and characterized. The third order nonlinear optical properties of the materials were studied using Z-scan technique with femtosecond Ti: sapphire laser with delivering pulses of 140 fs at 800 nm. The nonlinear optical refractive index was 9.29 × 10^?8 esu for 4BrCzP1 and 3.19 × 10^?7 esu for 4BrCzP2, respectively. While the third order nonlinear susceptibility was 1.29 × 10^?9 esu for 4BrCzP1 and 4.33 × 10^?9 esu for 4BrCzP2, respectively. The experimental results indicated that the hyperbranched polyfluorenes was a promising candidate in the application of third order nonlinear optical materials.     

Novel D–π–A dye sensitizers of polymeric metal complexes with triphenylamine or carbazole derivatives as donor for dye-sensitized solar cells: synthesis,characterization and application

Polymer Bulletin - In this paper, four novel D–π–A polymeric metal complexes as dye sensitizers for dye-sensitized solar cell, which have triphenylamine or carbazole derivative...     

Polyimide/nano-TiO2 hybrid films having benzoxazole pendent groups: In situ sol–gel preparation and evaluation of properties

Polyimide/titania (PI/TiO₂) nanocomposite films have been successfully fabricated through the in situ formation of TiO₂ within a PI matrix via sol–gel method. Poly(amic acid) (PAA), which is the precursor of PI, was successfully synthesized by mixing pyromellitic dianhydride (PMDA), with equimolar amount of a diamine monomer having a pendent benzoxazole unit and two flexible ether linkages in N,N-dimethylformamide (DMF) solvent. Tetraethyl orthotitanate [Ti(OEt)₄] and acetylacetone were then added to the resulted PAA. After imidization at high temperature, PI/TiO₂ hybrid films were formed. The structure and morphology of the hybrid nanocomposites with different titania contents (0 wt%, 5 wt%, 10 wt%, and 15 wt%) were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and transmission electron microscopy. The results indicate that the TiO₂ nanoparticles were homogeneously dispersed in the hybrid films. The thermogravimetric analysis of nanocomposites confirms the improvement in the thermal stability with the increase in the percentage of titania nanoparticle. Transmission electron microscopy showed that the nanoparticles with an average diameter of 25–40 nm were dispersed in the polymer matrix.     

Novel 3D scaffolds of chitosan–PLLA blends for tissue engineering applications: Preparation and characterization

This work addresses the preparation of 3D porous scaffolds of blends of chitosan and poly(l-lactic acid), CHT and PLLA, using supercritical fluid technology. Supercritical assisted phase-inversion was used to prepare scaffolds for tissue engineering purposes. The physicochemical and biological properties of chitosan make it an excellent material for the preparation of drug delivery systems and for the development of new biomedical applications in many fields from skin to bone or cartilage regeneration. On the other hand, PLLA is a synthetic biodegradable polymer widely used for biomedical applications. Supercritical assisted phase-inversion experiments were carried out in samples with different polymer ratios and different polymer solution concentrations. The effect of CHT:PLLA ratio and polymer concentration and on the morphology and topography of the scaffolds was assessed by SEM and Micro-CT. Infra-red spectroscopic imaging analysis of the scaffolds allowed a better understanding on the distribution of the two polymers within the matrix. This work demonstrates that supercritical fluid technology constitutes a new processing technology, clean and environmentally friendly for the preparation of scaffolds for tissue engineering using these materials.     

Novel rhenium‐based catalysts for dehydrocondensation of methane with CO/CO2 towards ethylene and benzene

A new family of rhenium‐based catalysts bearing HZSM‐5 zeolite exhibits remarkable performances for the catalytic dehydrocondensation of methane with CO/CO₂ towards ethylene, benzene, and naphthalene in high selectivity of above 90% at 1–3 atm and 973–1023 K. In contrast to Mo/HZSM‐5 catalysts, the EXAFS and TG/DTA/Mass studies reveal that the metallic Re on HZSM‐5 zeolite is a catalytically active and stable phase for the reaction. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the relative strength of adsorption of gases on carbon surfaces with functional groups: fluid–fluid,fluid–graphite and fluid–functional group interactions

Experiments at several temperatures were carried out for adsorption of non-polar and polar fluids on a highly graphitized carbon black, Carbopack F, which is composed of a basal plane of graphene and functional groups at the edges of the graphene layers. By comparing the experimental Henry constants with the theoretical Henry constants, calculated for adsorption on an ideal basal plane of graphite, we can determine the different relations and mutual influences between the various interactions, fluid–basal plane, fluid–functional group and fluid–fluid interactions, in the initial stages of adsorption.     

Two viologen-based crystalline photoactive complexes constructed by zinc chloride and N-(3-cyanophenyl)-4,4′-bipyridinium units: Structural arrangement of donor–acceptor units and photoresponsive characteristics

Two new photoinduced electron transfer supramolecular systems based on halometallate hybrid complexes are built by the combination of zinc chloride and N-(3-cyanophenyl)-4,4′-bipyridinium functional blocks. Photogenerated radicals and reversible photochromic cycles are observed for these molecular switches. Their photoresponsive characteristics are associated with the structural arrangements of the donor and acceptor units.     

Novel Langmuir–Blodgett film with ternary europium complex of long chain mono-eicosyl cis-butene dicarboxylate and 1,10-phenanthroline: Cooperative assembly and luminescence

Maleic anhydride is modified by two long chain alcohol (1-hexadecanol, 1-octadecanol) to the corresponding monohexadecyl cis-butene dicarboxylate (MAH) and monooctadecyl cis-butene dicarboxylate (MAO), respectively. Then the two ternary europium complexes with the as-derived long chain monoester and 1,10-phenanthroline (Phen) are synthesized and characterized. Furthermore the ultra thin luminescent Langmuir–Blodgett (LB) films have been prepared by using the subphase containing Eu³⁺ by the film-formation ability of long chain monoester, whose luminescence has been sensitized by phen. The layer structure of the LB films is demonstrated by low-angle X-ray diffraction and the AFM study reveals that the LB films are uniform and crack free, and the films mainly consist of closely packed lines or stripes. The LB films present characteristic luminescence of Eu³⁺, and the signal can be detected from a single layer.     

Novel supramolecular system of amphiphilic hyperbranched polymer with β-cyclodextrin and hyperbranched topography cavities: Synthesis and selective encapsulation

Novel supramolecular system of amphiphilic hyperbranched polymer with hyperbranched poly(β-cyclodextrin) core was designed and synthesized to accomplish a so-called selective encapsulation, where two types of guest molecules can be encapsulated into two types of molecular cavities from β-cyclodextrin (β-CD) and topography structure of hyperbranched polymer, respectively. The double molecular recognition behaviors from β-CD and hyperbranched cavities drive one guest to go into the former, the other guest to the latter. This selective encapsulation was further confirmed via the release profiles and sequences of Levofloxacin lactate (LL) and Phenolphthalein (PP). LL presents a sustained release period followed by an almost non-release stage, while PP releases on a quite slow rate at first, subsequently on the linearly increasing rate. At the early stage, the release of LL dominates in comparison with PP, and then the release rate of PP increases to play a determinate role in the release system. It can be attributed to the existence of two guests in the different molecular cavities with the different microenvironments. The observed selective encapsulation of supramolecular system is a new phenomenon, which is helpful to extend the application of CD-based hyperbranched polymers in supramolecular science and complex drug delivery system.     

Palladium Complex Immobilized on Magnetic Nanoparticles Modified with 2-Aminopyridine Ligand: A Novel and Efficient Recoverable Nanocatalyst for C–S and C–Se Coupling Reactions

Catalysis Letters - A novel, versatile and efficient magnetically recoverable palladium nanocatalyst [Fe3O4@SiO2/2-aminopyridine-Pd(II)] was fabricated via the immobilization of palladium(II)...     

Polyoxometalate–molybdenylacetylacetonate hybrid complex: A reusable and efficient catalyst for oxidation of alkenes with tert-butylhydroperoxide

The hybrid complex consist of molybdenylacetylacetonate complex covalently linked to a lacunary Keggin-type polyoxometalate, K₈[SiW₁₁O₃₉] (POM), was synthesized and characterized by elemental analysis, SEM, XRD, diffuse reflectance UV–Vis and FT-IR spectroscopic methods. The hybrid complex, [MoO₂(acac)–POM] (1), was used for alkene epoxidation with tert-BuOOH in 1,2-dichloroethane as solvent. The complex (1) can catalyze epoxidation of various olefins including non-activated terminal olefins. The effect of reaction parameters such as oxidant, solvent, and temperature on the epoxidation of cyclooctene was also investigated. This heterogeneous catalyst was reused several times in the oxidation of cyclooctene.     

Mechanistic modelling of kinetics and mass transfer for a solid–liquid system: Leaching of zinc with ferric iron

A systematic approach was developed to consider liquid–solid reactions with rough solid particles and shrinking particle model. The model is able to predict the reactivities of both non-porous and porous solid particles; the reaction order with respect to the solid material varies from zero (non-porous slab) to one (porous particle).As a model system, leaching of zinc sulphide (sphalerite) with ferric iron in an acidic environment was considered. The modelling was based on experimental data obtained in a batch reactor system, for which both conventional mixing and ultrasound was applied. Rival models based on plausible reaction mechanisms were derived and discriminated qualitatively and with regression analysis. The best model described the leaching reaction as a stepwise process, where ferric ions react with solid zinc sulphide in consecutive surface reaction steps. Shrinking particle model along with the surface roughness approach was used. The model predicts first order behaviour with respect to zinc sulphide, while the reaction order with respect to ferric iron varies from one to two as the reaction progresses. This is in accordance with experimental observations. The intrinsic kinetics, liquid–solid mass transfer and the effect of ultrasound were well described by the best kinetic model.     

Plasma and Silane Surface Modification of SiC/Si: Adhesion and Durability for the Epoxy–SiC System

Gaseous plasma pretreatments and surface derivatization using silane coupling agents (SCA) have been used to enhance the adhesive bonding of an epoxy to SiC-coated Si wafers (SiC/Si). The surface modification approaches included 1) an SCA treatment using 3-aminopropyltriethoxysilane (APS) or 3-glycidoxypropyltrimethoxysilane (GPS) and 2) an oxygen plasma pretreatment followed by a silane treatment. Durability was evaluated by immersing epoxy-coated SiC/Si samples in aqueous solutions at various pHs at 60°C for selected times. Adhesion durability for the epoxy-coated SiC/Si systems was qualitatively evaluated by visual inspection to identify debonding and quantitatively evaluated with a probe test to determine the critical strain energy release rate, G _c . Durability via either test approach varied as a function of surface treatment in this manner: oxygen plasma treatment plus silane modification > silane treated > no treatment. X-ray photoelectron spectroscopic characterization of surfaces was carried out following the surface treatments and after complete adhesion failure in the durability tests. The XPS results suggested that improved performance was due to plasma cleaning and modification of the substrate surface, promotion of silane surface interaction, and the formation of a thicker oxide layer.     

(Al3+, Nb5+) co–doped CaCu3Ti4O12: An extended approach for acceptor–donor heteroatomic substitutions to achieve high–performance giant–dielectric permittivity

Substitution of (Al³⁺, Nb⁵⁺) co–dopants into TiO₆ octahedral sites of CaCu₃Ti₄O₁₂ ceramics, which were prepared by a solid state reaction method and sintered at 1090 °C for 18 h, can cause a great reduction in a low–frequency loss tangent (tanδ≈0.045–0.058) compared to those of Al³⁺ or Nb⁵⁺ single–doped CaCu₃Ti₄O₁₂. Notably, very high dielectric permittivities of 2.9 ? 4.1 × 10⁴ with good dielectric–temperature stability are achieved. The room–temperature grain boundary resistance (R_gb≈0.37–1.17 × 10⁹ Ω.cm) and related conduction activation energy (E_gb≈0.781–0.817 eV), as well as the non–Ohmic properties of the co–doped ceramics are greatly enhanced compared to single–doped ceramics (R_gb≈10⁴–10⁶ Ω cm and E_gb≈0.353–0.619 eV). The results show the importance of grain boundary properties for controlling the nonlinear–electrical and giant–dielectric properties of CaCu₃Ti₄O₁₂ ceramics, supporting the internal barrier layer capacitor model of Schottky barriers at grain boundaries.     

A luminescent europium metal–organic framework with free phenanthroline sites for highly selective and sensitive sensing of Cu2 + in aqueous solution

A luminescent europium metal–organic framework [Eu(HL)(L)(H₂O)₂]·2H₂O (1) (H₂L = (2,3-f)-pyrazino(1,10)phenanthroline-2,3-dicarboxylic acid) with uncoordinated phenanthroline nitrogen sites was hydrothermally synthesized. It exhibits highly sensitive and selective sensing of Cu^2 + in aqueous solution. To the best of our knowledge, complex 1 is the first luminescent Eu-MOF with uncoordinated phenanthroline nitrogen sites for selective sensing of Cu^2 + in aqueous solution. The probable sensing mechanism was discussed in detail.     

Rheometers in scanning mode for cure of rubbers with low enthalpy: effect of heating rate and rubber–die contact

Abstract

Rheometers are usually run under isothermal conditions for the cure of rubbers, in spite of the following drawbacks: three experiments at least are necessary at different temperatures selected within a narrow temperature window, and it takes some time for thermal equilibrium to establish between the rubber sample initially at room temperature and the dies. In scanning mode, the dies of the rheometer and the sample should be heated from room temperature up to the selected final temperature at a constant rate. The effect of the value given to the heating rate, which is the main factor in this new method, is especially studied, as well as the quality of the contact between the dies and the sample. The rubber used in the present study is a natural rubber vulcanised with 2% sulphur with a low enthalpy. The kinetic parameters of this cure reaction have been previously determined by isothermal rheometry, and the enthalpy measured by calorimetry. The state of cure–temperature curves in scanning mode have been calculated using a numerical model taking into account the conduction heat transfer through the rubber, the coefficient of heat transfer at the die–rubber interface, and the kinetics of the heat evolved from the cure reaction with the enthalpy. The kinetic parameters are determined from the state of cure–temperature curves, which are similar to the torque–temperature curves, using a least squares method. The values of the kinetic parameters obtained by this last calculation, based on the mathematical treatment of these curves, are the same as those introduced for obtaining these curves using the numerical model. Thus, whatever the heating rate, ranging from 2 to 10 K min ^–1 , and the value of the coefficient of heat transfer at the die–rubber interface expressing the quality of the contact, in scanning mode the moving die rheometer (MDR) can be used to determine the kinetics of the cure of rubbers.