Synthesis and studies of mesomorphism of new octa-(benzo-15-crown-5)-substituted phthalocyanines and transition metal phthalocyaninates

Previously unknown octa-(benzo-15crown-5)-substituted phthalocyanine (1) and its metallocomplexes with Ni(II) (2), Co(II) (3), Cu(II) (4), Zn(II) (5), and Cd(II) (6) are synthesized. The possible formation of mesophases of these compounds is predicted and their mesomorphic properties are studied. It is found that compounds 1, 2, and 4 exhibit high-temperature enantiotropic mesomorphism typical of discotic mesogenes, which is well consistent with the predicted results. Free phthalocyanine (1) reveals dimesomorphism according to the DSC and thermomicroscopic data. According to the studies of miscibility of compound 1 with discotic mesogene, 2,3,6,7,10,11-hexa(cyclohexanebenzoyloxy)triphenylene, which exhibits nematic mesomorphism. The second phase transition is identified as the transition to a nematic phase. According to the texture of this mixture, compound 1 was classified with discotic mesogenes that form columnar nematics (N_Col). The first phase transition of 1 from a crystal to the mesophase was identified as columnar (Col). Phthalocyanines of cobalt (3) and copper(4) revealed latent mesomorphism according to the studies of their mixtures with the chiral nematic liquid crystal of cholesterin diphenylate.     

Octa- and tetra-(benzo-15-crown-5)phthalocyanines in surfactant-containing solutions

The behavior of octa-(benzo-15-crown-5)phthalocyanine (H₂cr₈Pc), as well as cobalt octa- and tetra-(benzo-15-crown-5)phthalocyaninates (Cocr₈Pc and Cocr₄Pc), in aqueous solutions containing cationic or anionic surfactants, such as cetyl trimethylammonium bromide (CTAB), sodium carboxymethyl cellulose (Na-CMC), and sodium dodecyl sulfate (SDS), is studied using electronic spectroscopy. The presence of eight benzo-15-crown-5 ether fragments on the periphery of the phthalocyanine ring is shown to facilitate the dissolution of Pc in an aqueous environment. The interactions between CTAB and crown-containing Pc promotes the dissolution of H₂cr₈Pc; Cocr₈Pc; and, to a lesser degree, Cocr₄Pc, which is accompanied by the appearance of molecular aggregates, including heteronuclear cofacial dimers. The presence of a metal in the ring is not the necessary condition of the process. In microscopically heterogeneous medium, such as an aqueous SDS-containing solution, H₂cr₈Pc is present in monomeric form at SDS concentrations close to C _cr and in dimeric form at SDS content below C _cr. Under similar conditions (environment, surfactant), Cocr₄Pc can exist in monomeric form at SDS concentrations much high than C _cr. The effect of the size of cation on the form of the crown-containing Pc in an aqueous solution is illustrated by an example of H₂cr₈Pc. Na-CMC promotes the dissolution of Pc and enables one to produce K⁺/Mcr₈Pc-modified films from aqueous solutions.     

Formation of surface layers upon evaporation of meso-tetra(benzo-15-crown-5)porphyrin on nanostructured iron surfaces

Morphology and spectral characteristics of the surface structures obtained upon the evaporation of meso-tetra (benzo-15-crown-5)porphyrin on the iron surface are studied with the use of digital optical microscopy, IR Fourier-transform spectroscopy, and x-ray diffraction analysis. During the interaction of porphyrin chloroform solution with nanostructured iron-based metal-oxide nanocomposite template, the process at the original template boundary is shown to initiate the formation of two polymorphous modifications of a porphyrin layer, namely, the aggregated layer and a transparent vitreous layer.     

Photorefractive and nonlinear optical properties of indium(III) tetra(15-crown-5)phthalocyaninate-based composites

Photoelectric, nonlinear optical, and photorefractive properties of hybrid composite materials based on polyvinylcarbazole (PVK) and indium(III) 2,3,9,10,16,17,23,24-tetra(15-crown-5)phthalocyaninate [(15C5)₄Pc]In(OH) are studied in detail. Field dependence of the quantum efficiency in a 7.8 μm-thick layer containing 5 at % [(15C5)₄Pc]In(OH) is measured. The best approximation of the quantum efficiency with Onsager’s equation corresponds to a quantum yield of thermalized electron-hole pairs φ₀ = 0.01 at initial separation r ₀ = 9.8 Å. Z-scan measurements in a nanosecond range showed that the electric susceptibility of [(15C5)₄Pc]In(OH) solution in tetrachloroethane (TCE) with a concentration of 7 × 10^?4 mol/L is χ⁽³⁾ = 1.34 × 10^?9 esu. The maximum coupling gain coefficient found for the material composed of PVK and 5 wt % [(15C5)₄Pc]In(OH) at an electric-field intensity of 200 V/μm is Γ = 80 cm^?1, and the difference between the coupling gain and absorption coefficients is Γ ? α = 70 cm^?1. The dependence of the coupling gain coefficient on the intensity ratio of interfering beams 1 and 2 (β = I ₁(0)/I ₂(0)) in a composite containing 3 wt % [(15C5)₄Pc]In(OH) is measured. An increase in β was attained by decreasing intensity of the signal beam I ₂(0) at constant intensity of the pump beam I ₁(0) = 0.15 W/cm² and E ₀ = 214 V/μm. Within the initial segment of the curve, the coupling gain coefficient increases from 30 to 60 cm^?1; then, the coefficient drops almost to the initial value. The data obtained show that the composite materials studied can be used in practice for correcting faded images. The combined analysis of the results obtained and similar data for gallium and ruthenium tetra-15-crown-5-phthalocyaninate complexes revealed the regularities in the change of the quantum yield of thermalized electron-hole pairs and the photorefractive coupling gain coefficient in a series of complexing metals: gallium(III), ruthenium(II), and indium(III). An increase in the molecular weight of the central metal atom is found to result in a substantial decrease in Γ and φ₀ due to the increase in the spin-orbit coupling constant.     

Photorefractive polymer composites based on ruthenium (II) tetra-15-crown-5-phthalocyanate axially coordinating ethylisonicotinate molecules photosensitive in telecommunication range

Polyvinylcarbazole layers containing ruthenium (II) tetra-15-crown-5-phthalocyanate axially coordinating ethylisonicotinate molecules are found to have photoelectric and photorefractive sensitivity at 1550 nm. The effect is determined by the formation of supramolecular ensembles with the electronic optical absorption and photoelectric sensitivity in the near IR range up to 1600 or 1700 nm and nonlinear optical properties. A photorefractive two-beam coupling gain coefficient Γ measured at 1550 nm increases with an increase in the Ru(II) complex content in the polymer layer and equals 25 cm⁻¹ at 6 wt %. The difference between the coupling gain and absorption coefficients (the actual gain coefficient) is Γ − α = 19 cm⁻¹. Additionally introducing 3 wt % C₆₀ fullerene into the layer does not change the characteristics, but the subsequent preirradiation (irradiation of the whole layer with a 633-nm laser beam in a range of the optical absorption of C₆₀ before recording photorefractive curves) results in an increase in the gain coefficient at 1550 nm up to Γ = 48.3 cm⁻¹ and, hence, in Γ − α = 42.3 cm⁻¹. A time constant of the diffraction grating formation is about τ = 0.8 s.     

Temperature dependence of optical properties of aluminum(III) <Emphasis Type=Italic>meso</Emphasis>-tetra(benzo-15-crown-5)porphyrinate solution in toluene

Aluminum(III) meso-tetra(benzo-15-crown-5)porphyrinate (AlClTCP) is produced from aluminum(III) chloride and meso-tetra(benzo-15-crown-5)porphyrin (H₂TCP) in boiling pyridine. The structure of the novel compound was determined by electronic absorption spectroscopy, nuclear magnetic resonance, and MALDI TOF mass spectrometry. The color of the AlClTCP solution in toluene was found to depend on temperature, namely, the heated solution is pink, while the cooled one is green. Changes in the electronic absorption spectra and fluorescence spectra of the solution depending on temperature are analyzed. According to the data of dynamic light scattering, gradual cooling of the AlClTCP solution in toluene heated to 120°C results in the formation of nanoparticles with a mean diameter of several hundred nanometers that assume a spherical shape. The self-assembly is assumed to take place via the change from the monodentate coordination of the chloride anion by Al³⁺ cation in AlClTCP molecules to a bridgelike coordination.     

Photoelectric, nonlinear optical, and photorefractive properties of polymer composites based on supramolecular ensembles of Ru(II) and Ga(III) complexes with tetra-15-crown-5-phthalocyanine

Techniques of the production of polymer nanocomposites based on tetrapyrrole compounds with photoelectric, nonlinear optical, and photorefractive properties are considered. Supramolecular ensembles of Ru(II) and Ga(III) complexes with tetra-15-crown-5-phthalocyanine are found to form upon the deposition of thin films from tetrachloroethane solutions that have undergone several cycles of heating followed by slow cooling. The surface formation of supramolecular ensembles is studied with the use of atomic force microscopy. The assemblage is found to give rise to photoelectric and photorefractive sensitivity in the near-infrared range (measurements were carried out at 1064 and 1550 nm). The quantum yield of thermalized electron-hole pairs at 1064 nm in composites of polyvinyl carbazole and assembled Ga(III) complexes is 20 times as high as that in composites based on Ru(II) complexes. The largest two-beam coupling gain coefficient at 1064 nm (Γ = 120 cm^?1 at E ₀ = 120 V/μm) was also observed for the Ga(III)-complex-containing composite. The third-order dielectric molecular susceptibility measured in tetrachloroethane solutions of the complexes weakly depends on the nature of the central atom and its axial neighborhood and falls in a range of γ = 4?5.2 × 10^?32 esu.     

Electrochemical impedance studies on the electrochemical properties of poly(3-methylthiophene) in aqueous solutions

Electrochemical impedance spectroscopy (EIS) measurements in a wide frequency range were used to study the electrochemical properties of poly(3-methylthiophene) (PMT) films. PMT was synthesized in acetonitril (AC) using BF₄⁻, ClO₄⁻ and CF₃SO₃⁻ as doping anion and Li⁺ as cation. The electrochemical characterization of these films was performed in aqueous solution using the same electrolyte for synthesis. Different parameters as electrolyte resistance, double layer capacitance, pore resistance, fractal dimensions, internal capacitance and charge resistance. SEM observation of PMT films provide strong evidence of the close relationship between type of electrolyte and their morphology, also is in good agreement with ac impedance results interpretation. The results are interpreted on the basis of models developed for intercalation electrodes in relation to the geometry and morphology of the polymer electrode. The results are discussed on the basis of the structural and chemical parameters of the anions and their interaction with the polymer. The discussion shows that the nature of the anion plays a major role on the electrochemical behavior of the polymer.     

The effect of hydrogen sulphide on ammonium bisulphite when used as an oxygen scavenger in aqueous solutions

The effectiveness of ammonium bisulphite (ABS) as oxygen scavenger and the behaviour of H₂S in brine/ABS solutions are examined. Deionised water, 1 wt.% NaCl and 3.5 wt.% NaCl with different ABS concentrations are bubbled with H₂S gas, while the dissolved oxygen, sulphide, E_H and pH are measured. With the exception of natural seawater, ABS concentration much greater than 100 ppmw (parts per million by weight) is needed to completely scavenge dissolved oxygen in all the solutions considered. The reaction between ABS and H₂S leads to increase in sulphide. The implications of the results for environment assisted cracking of oil and gas production tubings are discussed.     

The effects of anions on the behaviour of scratched iron electrodes in aqueous solutions

Two distinct types of electrochemical behaviour are observed when iron electrodes held at constant potential are rapidly scratched in the presence of reactive anions in aqueous solutions. The results presented here deal with the effects of bicarbonate, chloride and phosphate ions in alkaline solutions. Chloride and phosphate each accelerate the first oxidative step in the reaction by direct formation of adsorbed surface complexes with Fe(I). Bicarbonate does not accelerate the first oxidative step and does not complex with Fe(I) at a significant rate. It does, however, enter the second oxidative step by reacting at a significant rate with adsorbed FeOH to give an Fe(II) complex, thereby maintaining a bare reaction surface at higher potentials. The results are compared with those obtained in non-aggressive electrolytes of similar pH. In all cases the Fe(I) intermediate forms to complete monolayer coverage at potentials below the Fe/Fe(II) reversible potentials.     

The role of chelating agents on the corrosion mechanisms of aluminium in alkaline aqueous solutions

The influence of 1,2-diaminoethane (DAE) on the mechanism of aluminium corrosion in KOH solutions at pH 13 was investigated by combining time-resolved inductively coupled plasma optical emission spectrocopy, open-circuit potential measurements and X-ray photoelectron spectroscopy. In pure KOH solutions, a very slow corrosion rate is initially observed, corresponding to the dissolution of the native oxide layer. Following this incubation stage, the corrosion rate is increasing due to the formation and oxidation of Al hydride, until a steady state is reached. DAE behaves as a strong initial corrosion accelerator, due to synergistic effects with hydroxyl ions and a dissolution mechanism in three successive steps has been proposed: (i) a rapid initial dissolution induced by the formation and detachment from the surface of bidentate (chelate) Al-DAE metal bound surface complexes; (ii) a slower step ascribed to the formation and release of monodentate Al-DAE metal bound surface complexes and (iii) a final step dominated by direct oxidation of surface aluminium hydride by hydroxyl species as in pure KOH.     

The effect of preoxidation on the sulfidation of Ni-20Cr (2–5)Al Alloys

Ni-20Cr alloys with 2, 3.5, and 5 wt.% Al have been preoxidized up to 100 hr at 1000°C in dry H₂, in H₂/23% H₂O and in air and subsequently exposed to an H₂/5% H₂S atmosphere at 750° C. During the preoxidation treatment different types of oxide scales were formed which affect the sulfidation protection in different ways. Optimum results were obtained for alloys with 3.5 and 5 wt.% Al after 20 hr exposure to dry H₂ at 1000°C. A thin Al₂O₃ scale is formed which decreases the sulfur attack by more than one order of magnitude. Preoxidation conditions for Ni-20Cr-2Al alloys in H₂ and for Ni-20Cr-2Al and Ni-20Cr-3.5Al in H₂/H₂O were observed to be less effective. No improvement was found for preoxidation in air or for Ni-20Cr-5Al alloys preoxidized in H₂/H₂O.     

The effect of plasma spraying power on the structure and mechanical properties of hydroxyapatite deposited onto carbon/carbon composites

This paper deals with the effect of plasma spraying power on hydroxyapatite (HA) coatings on carbon/carbon composites (C/C composites). The microstructure and phase composition of the as-sprayed coatings have been examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The shear strength of the HA coatings–C/C substrates was detected on a RGD-5 tensile testing machine. Results indicate that the melting extent and the shear strength of the coatings were evidently improved with the increasing of spraying power. Moreover, the amount of decomposed phases is increased and the content of crystalline HA of coatings was slightly changed. Observation of fracture surfaces shows that carbon fiber bundles can bond well with HA coatings using 40 kW spraying power.     

The effect of purine on the corrosion of copper in chloride solutions

The influence of the concentration of purine (PU) on the corrosion and spontaneous dissolution of copper in 1.0 M NaCl solutions (pH 6.8) was studied. The investigations involved electrochemical polarization methods as well as weight-loss measurements, electrochemical quartz crystal microbalance (EQCM) techniques and scanning electron microscopy (SEM). The inhibition efficiency (IE) increases with an increase in the concentration of PU. An adherent layer of inhibitor is postulated to account for the protective effect. The adsorption of PU has been found to occur on the surface of copper according to the Langmuir isotherm. Purine is chemically adsorbed on the copper surface.     

The nature of the copper sulfide film grown on copper in aqueous sulfide and chloride solutions

In this paper, the properties of copper sulfide films formed both anodically and naturally in deaerated/anoxic aqueous sulfide and chloride solutions were investigated using a series of electrochemical and surface analytical techniques. A combination of cyclic voltammetric, corrosion potential (E_corr), and cathodic stripping voltammetric experiments showed that the sulfide film growth kinetics and film morphologies were controlled by the supply of SH⁻ from the bulk solution to the copper surface. There was no passive barrier layer observed on the copper surface under either electrochemical or corrosion conditions. The film morphology was dependent on the type and concentration of anions (SH⁻, Cl⁻) present in the solution. Scanning electron microscopy on both surfaces and focused ion beam-cut cross-sections showed the growth of a thin, but porous, base layer of chalcocite (Cu₂S) after short immersion periods (up to 2 hr) and the continuous growth of a much thicker crystalline outer deposit over longer immersion periods (≥36 hr), suggesting a solution species transport-based film formation process and the formation of an ineffective thin “barrier-type” layer on copper.     

Studies of physicochemical properties of modified carbon nanomaterials for sorption extraction of radionuclides. III. The effect of oxidizing treatment on sorption of Am(III) from aqueous solutions

The purpose of this work was to develop a method of manufacturing a new sorption material by soft oxidation of initial carbon materials with effective sorption characteristics with respect to americium. A technique of oxidation of FAS and VSK carbons is developed. Physicochemical properties of the obtained materials are studied, the micropore size and volume are determined, and IR spectra of samples are studied. Sorption of Am (III) is studied under various conditions. It is established that oxidizing treatment of FAS increases its sorption ability in respect to Am(III).     

The effect of 180 °C-annealing on the electrochemical behavior of nano-thick zinc-electroplated copper in aqueous solutions with different pH

The anodic polarization and a.c. impedance measurements of 4 nm- and 25 nm-zinc-electroplated copper specimens were conducted in aqueous solutions with four different pH-values. The nano-thick zinc-electroplated copper was tested after electroplating and annealing at 180 °C for 1, 2 and 3 h, respectively. The results showed that the open-circuit potential (OCP) of 25 nm-zinc electroplated copper shifted toward noble potential after annealing. A more noble OCP of 25 nm zinc-electroplated copper could be achieved when zinc plated copper was annealed at 180 °C up to 1 h. Similar change was found for 4 nm-zinc electroplated copper only in neutral and alkaline solutions. The a.c. impedance response of all nano-thick zinc-electroplated copper corresponded to two Randle’s circuits in series, in which the circuit measured in a high frequency region of their Nyquist diagrams revealed the electrochemical behavior of nano-thick zinc deposits. The charge transfer resistance of the nano-thick zinc electroplated copper was significantly raised after annealing at 180 °C when tested in pH 9.5 solution. Microstructures of the aforementioned nano-thick zinc electroplated copper were examined with cross-sectional TEM specimens. A distinct phase interface between zinc and copper was observed for as plated specimens, while alloying of zinc and copper at the interface was detected after annealing at 180 °C for 1 h. Electroplated zinc diffused into the copper foil during the 180 °C-annealing and the corrosion potential of the anodic polarization curve indicated the condition of the alloy surface. The annealing effect of 4 nm- and 25 nm-zinc electroplated copper specimens could be related to the results of electrochemical measurement.     

The effect of (ZrB2-SiC) addition on microstructure and mechanical properties of NbMo-matrix composites fabricated by hot-pressing

The effects of (0–60%) vol% (70 vol% ZrB₂ + 30 vol% SiC) additions on microstructure and properties of NbMo substrate fabricated by hot-pressing were studied at room temperature. Types of formed phase were decided by the amount of ZrB₂ and SiC additives. The effective eutectic phase was observed in 15 vol% (70 vol% ZrB₂ + 30 vol% SiC)-NbMo, which was attributed to the addition of SiC. 30 vol% (70 vol% ZrB₂ + 30 vol% SiC)-NbMo had the highest relative density of 98.69%. Compared with x ZrB₂-NbMo composites, the addition of SiC could further improve the hardness of NbMo_ss in x (70% ZrB₂ + 30% SiC)-NbMo when the value of x was same, and NbMo_ss in 60 vol% (70 vol% ZrB₂ + 30 vol% SiC)-NbMo had the highest hardness of 6.82 GPa. Only the 15 vol% (70 vol% ZrB₂ + 30 vol% SiC) addition could improve the compressive strength of NbMo matrix. The reasons for the low strength of 30, 45, 60 vol% (70% ZrB₂ + 30% SiC)-NbMo were the lack of ductile phase and the large amount of hard phase production.     

The influence of different aggressive anions on the electrochemical behaviour of aluminium in sodium nitrate aqueous solutions

The effects of different experimental parameters influencing the determination of critical pitting and protection potentials of aluminium and its alloys have been studied by potentiostatic and potentiodynamic methods. The resistance of aluminium against corrosion in aqueous media can be attributed to a rapidly formed surface oxide film. The addition of the aggressive anions like: chloride, thiocyanide, hydroxyl, sulphide, formate, and acetate (Cl⁻, SCN⁻, OH⁻, S²⁻, HCOO⁻ and CH₃‐ COO⁻) lead to extensive localized attack in all of the cases. The breakdown of the passive film takes into account the migration of aggressive anions through the film. Breakdown occurs when aggressive anions reach the metal‐film interface. E_π is the critical pitting potential, E_p ist the protection potential and the pitting can be formed only in the E_π–E_p polarization range as it was proved in many experiments [1–3]. The most likely action mechanism of aggressive anions is not a complete dissolution of the film, nor penetration of aggressive anions through solid oxide as suggested for nickel and iron [4]. It is more likely to be somewhere in between the two i.e. action of aggressive anions is that of complexing aluminium ions and pulling in water to hydrate the layer in a way similar to that occurring at cathodic hydrogen evolution, where such dramatic increase of hydrogen evolution rate is observed after a certain cathodic potential is reached. Localized corrosion can be prevented by the action of adsorptive inhibitors which prevent the adsorption of the aggressive anions or by the formation of a more resistant oxide film on the metal surface. The corrosion mechanism is not modified by the addition of ammonium rhodanide but only slowed down.