Surface Modification of Silicone Rubber by CF<Subscript>4</Subscript> Radio Frequency Plasma Immersion

Silicone rubber samples were treated by CF₄ capacitively coupled plasma at radio frequency (RF) power of 60, 100 and 200 W for a treatment time up to 20 min under CF₄ flow rate of 20 sccm, respectively. Static contact angle, ATR-FTIR and XPS, and AFM were employed to characterize the changes of surface on hydrophobicity, functional groups, and topography. The results indicate the static contact angle is improved from 100.7 to 150.2°, and the super-hydrophobic surface, which corresponds to a static contact angle of 150.2°, appears at RF power of 200 W for a 5 min treatment time. It is suggested that the formation of super-hydrophobic surface is ascribed to the co-action of the increase of surface roughness created by the ablation reaction of CF₄ plasma and the formation of [–SiF _x (CH₃)_2−x –O–] _n (x = 1, 2) structure produced by the direct attachment of F atoms to Si.     

The role of new functional groups in the surface layer of LDPE during its high-voltage contact polarization

New functional groups containing Al-C bonds and Al₂O₃ molecules are formed in the surface layer of the polymer during depositing of aluminum on polyethylene films. This effect is absent when Au is deposited on the films. For capacitors with Al and Au electrodes, processes of high-voltage contact polarization and conductivity are studied at various configurations of the external electric field. If Al-C organometallic bonds and Al₂O₃ or, for example, Al-O-C bonds are formed in the surface layer during application of high electric fields, a number of dielectric “anomalies” are observed. They manifest themselves as the fact that an increase in the amount of cycles of a bipolar saw-tooth voltage is accompanied by a marked increase in the residual surface charge density. At such a configuration of the external field, a decrease in its frequency (for region, where dE/dt > 0) leads to a marked reduction in high-voltage dielectric permittivity to negative values. This phenomenon is explained by the fact that, along with the external field, an internal field appears owing to formation of the space charge near metal/polymer boundaries.     

First principle electric field response of single-walled boron nitride nanotube: a case study of zigzag (4,0) model

Structural and electrical responses of the (4,0) zigzag model of single-walled boron nitride (BN) nanotube (NT) (with edges terminated by H atoms) have been investigated under the external electric fields (parallel and transverse) with strengths 0−2.0 × 10⁻² a.u. using DFT-B3LYP/6-31G* method. Calculated electric dipole moment shows a significant change in the presence of the parallel and perpendicular external electric fields which result in much stronger interactions at higher electric field strengths. Natural bond orbital (NBO) atomic charges analysis shows that the separation of the center of the positive and the center of the negative electric charges of (4,0) zigzag BNNT increase with increase the applied parallel and transverse electric field strengths. The applied fields change the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies and decrease the HOMO–LUMO gap (HLG) values. The calculated electronic spatial extent (ESE) showed small changes of <0.63% and <1.53% over the entire range of the applied parallel and perpendicular electric field strengths, respectively. Results of this study indicate that the properties of BNNTs can be controlled by applying the proper external electric field. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Impedance studies on the 5-V cathode material,LiCoPO<Subscript>4</Subscript>

Olivine-structured LiCoPO₄ is synthesized by a Pechini-type polymer precursor method. The structure and the morphology of the compounds are studied by the Rietveld-refined X-ray diffraction, scanning electron microscopy, Brunauer, Emmett, and Teller surface area technique, infrared spectroscopy, and Raman spectroscopy techniques, respectively. The ionic conductivity (σ ionic), dielectric, and electric modulus properties of LiCoPO₄ are investigated on sintered pellets by impedance spectroscopy in the temperature range, 27–50 °C. The σ (ionic) values at 27 and 50 °C are 8.8 × 10⁻⁸ and 49 × 10⁻⁸ S cm⁻¹, respectively with an energy of activation (E _a) = 0.43 eV. The electric modulus studies suggest the presence of non-Debye type of relaxation. Preliminary charge–discharge cycling data are presented.     

Effect of external fields applied during hot-water treatment on the aspect ratio of nanocrystallites formed on SiO<Subscript>2</Subscript>·TiO<Subscript>2</Subscript> coatings derived from sol–gel techniques

SiO₂·TiO₂ coatings were prepared by a sol–gel route. The effect of the external fields including mechanical vibration and electric charge applied during hot-water treatment on titania precipitation at the surface of the coatings was investigated. The shape of the resulting precipitates tended to elongate by applying vibration in a parallel or perpendicular direction, or by applying an electric charge. The organization of titania nanocrystallites possibly occurs because of the concentration gradient of dissolved titania species generated by the external fields during the hot-water treatment. A maximum aspect ratio of 38.1 was achieved for the precipitate prepared by hot-water treatment performed under parallel vibration for 5 h. The shape of the resulting precipitates was also influenced by the content of TiO₂ in the SiO₂·TiO₂ coating, with a smaller proportion of TiO₂ increasing the aspect ratio of the resulting precipitate.     

Chemisorption of SO<Subscript>2</Subscript> on the Zn-modified In<Subscript>2</Subscript>O<Subscript>3</Subscript> surface

Chemisorption of SO₂ and O₂ on the In₂O₃ surface containing a zinc additive (0.4–2.7 at.%) was studied in a temperature range of 22–200 °C. At least three forms of sorbed SO₂ exist on the modified In₂O₃ surface. The temperature affects the contribution of single forms of SO₂ sorption and, hence, the change in the electric conductivity. The preliminary sorption of O₂ favors the formation of a donor form of chemisorbed SO₂. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2228–2232, October, 2005.     

Synthesis of TiO<Subscript>2</Subscript> using different hydrolysis catalysts and doped with Zn for efficient degradation of aqueous phase pollutants under UV light

In this work, various TiO₂ and TiO₂ doped with 0.1, 1.0, and 5.0 mol% of Zn were prepared by the sol–gel method varying different hydrolysis catalysts (HNO₃, OHAc, H₃PO₄) in order to be used as photocatalysts for environmental applications. The X-ray diffraction results showed that the different TiO₂ samples have presented the anatase as main phase, However, the acid nature has played an important role in the superficial and optical properties. The N-physisortion analysis has revealed that the specific surface area of calcined TiO₂ samples prepared using H₃PO₄, HOAc, and HNO₃ was 245, 100, and 90 m² g⁻¹, respectively, while the spectroscopic UV analysis, the band gap energy has shifted by 3.3–3.0 eV. In order to improve the optical properties of TiO₂, the last preparation was doped with different zinc concentrations. The result showed that, as the Zn concentration increase by 0.1–5.0 mol%, the surface area increased from 90 to 120 m² g⁻¹. Nevertheless, the E _g returned from 3.0 to 3.32. The SEM analyses have not revealed important morphological changes between no doped and doped materials. The catalytic activity of the composite was studied on the photocatalytic degradation of 2,4-Dichlorophenoxyacetic acid (2,4-D) and the activity results showed that small Zn concentrations decrease the t _1/2 in 28 min.     

On determination of the strength of local electric fields at the bromine atoms in the series of compounds BrCH2R by79Br NQR spectroscopy

The values of changes in the strength of local electric fields at the bromine atoms for a series of compounds BrCH₂R were determined from a hyperbolic equation relating the⁷⁹Br NQR frequencies to their field constants. The totalities of electron-acceptor and electrodonor substituents R are described by equations of the same type differing in their parameters. Deceased. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1150–1154, June, 1998.     

Photocatalytic production of hydrogen in systems based on Cd<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>S/Ni<Superscript>0</Superscript> nanostructures

A relation was established between the composition of Cd _x Zn_1–x S nanoparticles and their ability to accumulate excess negative charge during irradiation. The rate of expenditure of the accumulated charge depends on the composition of the nanoparticles and is determined by their electric capacitance. A correlation was found between the photocatalytic activity of the Cd _x Zn_1–x S nanoparticles in the release of hydrogen from solutions of Na₂SO₃, their composition, and their capacity for photoinduced accumulation of excess charge. It was shown that Ni⁰ nanoparticles photodeposited on the surface of Cd _x Zn_1–x S are effective cocatalysts for the release of hydrogen. It was found that Zn^II additions in photocatalytic systems based on Cd _x Zn_1–x S/Ni⁰ nanostructures have a promoting action on the release of hydrogen from water–ethanol mixtures. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 1, pp. 8–16, January-February, 2009.     

Dependence of the magnetic properties of MnGaN epitaxial layers on external electrical field

Investigation of the magnetic properties of MnGaN epitaxial layers as a function of external electrical field was performed on the basis of field effect structure. The structure included substrate of n-type GaN, epitaxial layer of n-type Mn_xGa_1-xN, dielectric layer and metal layer acting as field effect device gate. Each Mn atom in Mn_xGa_1-xN contributes 4 net spins due to the electrons occupying energy levels ⁴F, ⁴D, ⁴P and ⁴G belonging to 3d orbital, and these levels are in the energy band gap and in the top of the valence band of Mn_xGa_1-xN. The position of the Fermi level is determined to be in the energy band gap of the layer of GaN and to be above the level 4F in the layer of Mn_xGa_1-xN. In this way application of external negative voltage on the gate causes change in the number of electrons contributing net spins and the saturation magnetization M_sat of Mn_xGa_1-xN changes as well. It was found that M_sat changes in the range 1.15 × 10⁻³–0.7 × 10⁻³ A μm⁻¹ if the external voltage changes in the interval 0–−5V. The application of this structure for the design of spintronic devices is discussed in this paper.      

Immobilization of Rhodococcus AJ270 and Useof Entrapped Biocatalyst for the Productionof Acrylic Acid

Summary.  Rhodococcus AJ270 is adsorbed by Dowex 1 at 15.4  mg dry weight per g resin with maximum amidase specific activity observed at lower loadings. Bacteria form a monolayer on the resin surface, and adsorption is complete within 2 min. AJ270 can be entrapped in agar and agarose gels (optimum loading: 20 mg dry weight bacteria per cm³ gel). Adsorption and entrapment improve amidase thermal stability 3–4 fold, and entrapment shifts the pH optimum from 8 to 7. Adsorbed and free bacteria show similar values for K _m and V _max, but entrapped bacteria have higher K _m values. Compared with bacteria adsorbed to Dowex, the activity per cm³ of matrix of agar-entrapped AJ270 is eight-fold higher. In stirred-tank reactors, exposure to acrylic acid reduces the amidase activity of the biocatalyst in the hydrolysis of acrylamide. In column reactors, entrapped AJ270 suffers little reduction in amidase activity against 0.25 M acrylamide over 22 h continuous operation. Received November 18, 1999. Accepted December 14, 1999     

Hydrothermal synthesis of nanostructured MnO2 under magnetic field for rechargeable lithium batteries

Nanocrystalline MnO₂ was synthesized by the hydrothermal method with or without pulsed magnetic fields. It was found that the morphology of the MnO₂ prepared without magnetic field has an urchin-like structure, while the MnO₂ prepared with magnetic fields has a rambutan-like structure. A pronounced increase in the Brunauer–Emmett–Teller specific surface area was obtained when the intensities of the pulsed magnetic fields increased. The battery performances were improved for the samples prepared with magnetic fields. The MnO₂ prepared under a magnetic field of 4 T shows a capacity of 121.8 mAh g⁻¹, while the MnO₂ prepared without magnetic field only shows 103.0 mAh g⁻¹ after 30 cycles.     

Facile preparation and electrochemical properties of large-scale Li<Subscript>1+<Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript> nanobelts

Large-scale Li_1+x V₃O₈ nanobelts were successfully fabricated using filter paper as deposition substrate through a simple surface sol–gel method. The nanobelts were as long as tens of micrometers with widths of 0.4–1.0 μm and thickness of 50–100 nm. The nanobelts were characterized by X-ray diffration (XRD), Fourier infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM). The formation mechanism of the nanobelts was investigated, showing that the morphology of the nanobelts is mainly determined by the calcination temperature. Electrochemical properties of the Li_1+x V₃O₈ nanobelts were characterized by charge–discharge experiments, and the results demonstrate that the Li_1+x V₃O₈ nanobelts exhibit a high discharge capacity (278 mAh g⁻¹) and excellent cycling stability.     

Local structure and photoluminescent characteristics of Eu<Superscript>3+</Superscript> in ZnO–SiO<Subscript>2</Subscript> glasses

The photoluminescence properties of xZnO–(100−x)SiO₂ (x = 0, 5, 10, 20) containing 1% Eu₂O₃ prepared by a sol–gel method were systematically investigated. The results indicated that the relative proportion of f–f transitions to charge transfer (CT) absorption decreased with the increase of ZnO concentration. The intensity of ⁵D₀–⁷F_J transitions of Eu³⁺ ions was enhanced with the increase of ZnO content due to local structure changes and decreased quantities of Eu³⁺ ions clusters. The results of fluorescence line narrow (FLN) spectra indicated that Eu³⁺ ions occupied one site in SiO₂ glass and two sites in ZnO–SiO₂ glasses. The second-order crystal field parameters were calculated. B₂₀ and B₂₂ for site 1 increased with excitation energy, while ones hardly changed for site 2.     

Preparation and electrical properties of Nd and Mn co-doped Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films

Ferroelectric thin films of Nd and Mn co-doped bismuth titanate, Bi_3.15Nd_0.85Ti_3−x Mn _x O₁₂ (BNTM) (x = 0–0.1), were fabricated on Pt/TiO₂/SiO₂/Si(100) substrates by a sol–gel technique. The BNTM films had a polycrystalline perovskite structure and uniform and dense surface morphologies. A lattice distortion was observed in the BNTM films due to Mn ion doping. The ferroelectric measurement of the films indicated that the values of coercive field (E _c ) decreased gradually with the increase of the Mn content (x), however, the remanent polarization (P _r ) increase firstly and then decrease with the increase of x. The sample with x = 0.05 had optimum electrical properties and a maximum 2P _r value. The 2P _r and 2E _c values of the film at a maximum applied electric field of 400 kV/cm were 38.3 μC/cm² and 180 kV/cm, respectively. Moreover, this BNTM capacitors did not show fatigue behaviors after 1.0 × 10¹⁰ switching cycles at a frequency of 1 MHz, suggesting a fatigue-free character. The main reason for the increase of the 2P _r and the decrease of the 2E _c might be attributed to the lattice distortion in BNTM films due to Mn ion doping.     

LiNi<Subscript>0.8</Subscript>Co<Subscript>0.2−x</Subscript>Ti<Subscript>x</Subscript>O<Subscript>2</Subscript> nanoparticles: synthesis,structure, and evaluation of electrochemical properties for lithium ion cell application

Layered Ti-doped lithiated nickel cobaltate, LiNi_0.8Co_{0.2 − x}Ti_xO₂ (where x = 0.01, 0.03, and 0.05) nanopowders were prepared by wet-chemistry technique. The structural properties of synthesized materials were characterized by X-ray diffraction (XRD) and thermo-gravimetric/differential thermal analysis (TG/DTA). The morphological changes brought about by the changes in composition of LiNi_0.8Co_{0.2 − x}Ti_xO₂ particles were examined through surface examination techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. Electrochemical studies were carried out using 2016-type coin cell in the voltage range of 3.0–4.5 V (vs carbon) using 1 M LiClO₄ in ethylene carbonate and diethyl carbonate as the electrolyte. Among the various concentrations of Ti-doped lithiated nickel cobaltate materials, C/LiNi_0.8Co_0.17Ti_0.03O₂ cell gives stable charge–discharge features.     

Influence of solvent structure on the aquation of <Emphasis Type="BoldItalic">trans</Emphasis>-[Ru(3-MePy)<Subscript>4</Subscript>Cl<Subscript>2</Subscript>] complex in mixed aqueous solvents

The kinetics of the solvolytic aquation of trans-[Ru (3-Me Py)₄Cl₂] was studied spectrophotometrically in water – isopropanol in the range (30–90% v/v), and water acetonitrile in the range (10–70% v/v), and in the temperature range 50–65 °C. Plots of log k versus the reciprocal of the relative permittivity and Grunwald–Winstien gave non-linear plots. This non-linearity is derived from a large differential effect of solvent structure between the initial and transition states. The plot of log k versus water concentration was also non linear; evidence for the presence of a S _N ¹ mechanism. However, extrema in the variation of enthalpy ΔH* and entropy ΔS* of activation correlate well with the extrema in physical properties of the mixtures which are related to changes in solvent structure. Linear plots of ΔH* versus ΔS* were obtained and the iso- kinetic temperature indicates that the reaction is entropy controlled.     

Combined laser and magnetic field treatment of YFeO<Subscript>3</Subscript>—containing films grown by spray-pyrolysis

Thin films (50–1200 nm) of YFeO₃ were deposited on fused silica substrates by spray-pyrolysis using ethylene glycol solution of Y-Fe(III) citric complexes. The films were post deposition annealed at 750°C in static air for 2 h. Films obtained in this way were afterwards irradiated by a burst mode operated Nd-YAG laser (pulse energy 650 mJ, pulse duration 700 μs, energy density 110 mJ/cm²). The laser’s onset was synchronized with that of a magnetic field pulse of nearly square shape (magnetic induction 0.5 T, pulse duration 900 μs). The samples were placed normally to the direction of the magnetic field. The treatment does not affect the phase composition of the film but significantly increases the crystallite sizes of the phases presenting in the sample. The saturation magnetization of the films decreases as a result of the laser and magnetic field treatment and the coercive force increases by 50%.     

Effect of Cr doping on the ac electrical properties of MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

Magnesium aluminate nanoparticles with different chromium concentration (0–12%) have been synthesized by a citrate–nitrate sol–gel route. X-ray diffraction studies confirmed the formation of single-phase cubic spinel structure excluding the presence of any secondary phase. Crystallite size of the synthesized nanoparticles was found to increase from 8.5 to 19.8 nm with the increase in Cr concentration. Fourier transformed infrared spectroscopic studies confirmed the presence of AlO₆ group which led to the formation of MgAl₂O₄ spinel structure. Surface morphology of the sintered pellets was investigated with the help of a field emission scanning electron microscope which revealed the existence of both grain and grain boundary along with their aggregates. The dielectric constant, dielectric loss and ac conductivity were studied as a function of frequency of the applied electric field for different composition and their nature of variation with frequency has been elucidated on the basis of Maxwell–Wagner interfacial model. Impedance spectroscopy technique has been used to study the effect of grain and grain boundary on the electrical properties of this spinel oxide. All the electrical parameters showed strong dependence on the nanostructural properties and were found to vary consistently with the increase of doping concentration.     

Phase Transitions and Critical Behaviour of Binary Liquid Mixtures

 Compared to the simple one-component case, the phase behaviour of binary liquid mixtures shows an incredibly rich variety of phenomena. In this contribution we restrict ourselves to so-called binary symmetric mixtures, i.e. where like-particle interactions are equal (Φ₁₁(r) = Φ₂₂(r)), whereas the interactions between unlike fluid particles differ from those of likes ones (Φ₁₁(r) ≠ Φ₁₂(r)). Using both the simple mean spherical approximation and the more sophisticated self-consistent Ornstein-Zernike approximation, we have calculated the structural and thermodynamic properties of such a system and determine phase diagrams, paying particular attention to the critical behaviour (critical and tricritical points, critical end points). We then study the thermodynamic properties of the same binary mixture when it is in thermal equilibrium with a disordered porous matrix which we have realized by a frozen configuration of equally sized particles. We observe – in qualitative agreement with experiment – that already a minute matrix density is able to lead to drastic changes in the phase behaviour of the fluid. We systematically investigate the influence of the external system parameters (due to the matrix properties and the fluid–matrix interactions) and of the internal system parameters (due to the fluid properties) on the phase diagram.