Electrochemical properties of polyaniline in p-toluene sulfonic acid solution

Polyaniline was deposited potentiodynamically on a stainless steel substrate in the presence of an inorganic acids (sulfuric acid). The electrochemical characterization of the electrode was carried out by means of cyclic voltammetry and electrochemical impedance spectroscopy in the organic acids (p-toluene sulfonic acid) solution. The results show that polyaniline has a high specific capacitance of 431.8 F g⁻¹ at 1 mV s⁻¹, high coulombic efficiency of 95.6% at 20 mV s⁻¹, and exhibits a high reversibility. This indicates the promising feasibility of the polyaniline used as an electrochemical capacitor material in the electrolyte of p-toluene sulfonic acid solution especially at high charge–discharge process.     

Simulation of equivalent weight dependence of Nafion morphologies and predicted trends regarding water diffusion

Microphase separation within hydrated Nafion^® membranes was simulated using Dissipative Particle Dynamics (DPD). Morphologies were obtained at branching densities corresponding with equivalent weights ranging from 800 to 1400 (g/mole SO₃) and water percentage volume contents ([H₂O]) varying between 10% and 30%. All cases showed pronounced microphase separation involving a hydrophobic Teflon phase and a hydrophilic phase in which water is associated with SO₃ groups that are located near the phase boundaries. Pore morphologies were found to depend strongly on water content and branching density. The average pore radius (R_pore) and the distance between the pores (D_cl-cl) were found to increase with water content obeying the relations R_pore = 1.3 + α[H₂O] (nm), and D_cl-cl = 3.2 + β[H₂O] (nm). The values of the expansion coefficients α and β decrease linearly with branching density with α = 5.3 × 10⁻⁵ × (EW-450) and β = 1.3 × 10⁻⁴ × (EW-450) nm/vol%. For decreasing branching density the pores obtain a more spherical character. The consequence of this on water diffusion is estimated by employing Monte Carlo trajectory calculations in which we assume that water movement is confined within the hydrophilic phase and local water mobility to be equal to that of pure water. The estimated diffusion constants increase linearly with branching density (i.e. linear decrease with equivalent weight). Experimental water diffusion constants obtained from literature for Nafion1100 membrane are in good agreement with our calculations. A counterintuitive picture evolves in which smaller pores lead to enhanced water diffusion.     

Multiple-scattering approach to Sn L3-edge X-ray absorption near-edge structure (XANES) analyses for organic tin compounds

We apply multiple-scattering calculations to the analyses of Sn L₃-edge X-ray absorption near-edge structure (XANES) spectra for environmental organotin compounds such as SnCl_4−nMe_n, SnCl_4−nBt_n, and SnCl_4−nPh_n (n = 0–4) where Me = CH₃, Bt = C₄H₉, and Ph = C₆H₅. The XANES peak at 3960 eV has rich information on the local structure. Referring to the optimized structures by density functional theory (DFT) calculations, multiple-scattering calculations well explain the observed spectral changes for different “organic extents”. The present study also supports the widely-used semiempirical rule called ‘Natoli’s rule’ for these environmental compounds, which will be useful to use XANES spectra for the practical analytical tools.     

Synthesis, characterization and radiolytic properties of bis(oxalato)borate containing ionic liquids

Previously unreported bis(oxalato)borate (BOB) ionic liquids (ILs) containing imidazolium, pyridinium, and pyrrolidinium cations were prepared from the corresponding halide salts by reaction with sodium bis(oxalato)borate (NaBOB), and their properties are reported. Pulse radiolysis experiments revealed that the BOB anion scavenges solvated electrons with rate constants of 3×10⁸ M⁻¹ s⁻¹ in the ionic liquid C₄mpyrr NTf₂ and 2.8×10⁷ M⁻¹ s⁻¹ in water. This reactivity indicates that BOB ILs may be too sensitive to be used as neat solvents for nuclear separations processes in high radiation fields but may still be useful for preventing criticality while processing relatively “cold” fissile actinides.     

Reduced N-methyl-pyridylethynyl porphyrins exhibit strong near-IR absorptions

Porphines bearing two N-methyl-4-pyridylethynyl substituent reversibly undergo two one-electron reductions at room temperature. The anion radicals and di-anions show diminished visible bands (450 nm and 600–700 nm) and intense absorptions in the 800-nm and 1100-nm region, respectively. Some of the near-IR bands have extinction coefficients greater than 1.5 × 10⁵ M⁻¹ cm⁻¹.     

Isoconversional kinetics of degradation of polyvinylpyrrolidone used as a matrix for ammonium nitrate stabilization

Thermogravimetric analyzer (TGA) has been applied to measure the kinetics of the thermal degradation of virgin polyvinylpyrrolidone (PVP) and a phase stabilized PVP–ammonium nitrate (AN) material. The PVP–AN samples have been prepared by using 20 wt.% of AN and PVP of three different molecular weights. Virgin PVP undergoes a major mass loss in the region 380–550 °C leaving a small amount of nonvolatile residue. The application of an advanced isoconversional method to the respective degradation process demonstrates that its effective activation energy increases from 70 kJ mol⁻¹ to a plateau value at 250–300 kJ mol⁻¹, which is independent of the molecular weight. The PVP–AN materials lose spontaneously 20% of their mass on heating above the glass transition temperature of the PVP matrix (160–180 °C). After the escape of AN, the remaining PVP matrix degrades in the same temperature region as virgin PVP, however, the effective activation energy of this degradation is 150–200 kJ mol⁻¹.     

Ultrafast dynamics of heat flow across molecules

An ultrafast flash thermal conductance apparatus is used to study heat flow through aliphatic and aromatic molecules arranged in self-assembled monolayers (SAMs). The apparatus consists of a thin metal film which can be flash-heated by many hundreds of degrees in 1 ps using a femtosecond pulse. Heat flow from the metal surface into the SAM molecules is detected using vibrational sum-frequency generation (SFG) spectroscopy. The SAMs studied were alkanethiolates (AT) ranging from C6 to C24, benzenethiolate (BT) and benzylmercaptide (BMT). SFG in the CH-stretch region selectively probes transitions of the terminal methyl groups of AT and the CH moiety at the 4-position of the phenyl ring of BT and BMT (opposite the thiolate-surface bond). The SFG signal is sensitive to temperature-jump induced thermal disorder of the SAM and also to vibrational frequency shifts induced by the changing intramolecular vibrational populations. The SFG probe functions as a thermometer, and this thermometer is 1.5 Å thick with a response time of 1 ps. In the AT chains, a study of the length dependence is used to determine the rate heat flows across the metal–SAM interface and the rate of heat flow through the AT chains. The interface thermal conductance is 220 GW m⁻² s⁻¹. The AT molecular conductance is 50 pW K⁻¹ or 0.3 eV s⁻¹ K⁻¹. Heat flow through the AT chains is ballistic with a velocity of 1 km/s. Heat flow into BMT is slower than in BT because BMT has one additional methylene linker group. The BT and BMT structures evidence a thermally-initiated surface rearrangement occurring in a few tens of picoseconds. These SAMs are strained and the phenyl rings cannot adopt the most stable staggered herringbone structure. After the T-jump, the SAM molecules have enough freedom to relax into more favorable configurations.     

Interaction and photodynamic activity of cationic porphyrin derivatives bearing different patterns of charge distribution with GMP and DNA

The interaction of amphiphilic cationic porphyrins, containing different patterns of meso-substitution by 4-(3-N,N,N-trimethylammoniumpropoxy)phenyl (A) and 4-(trifluoromethyl)phenyl (B) groups, with guanosine 5′-monophosphate (GMP) and calf thymus DNA have been studied by optical methods in phosphate buffer solution. The properties of these synthetic porphyrins were compared with those of representative standard of anionic 5,10,15,20-tetra(4-sulphonatophenyl)porphyrin (TPPS₄⁴⁻) and cationic 5,10,15,20-tetra(4-N,N,N-trimethylammonium phenyl)porphyrin (TMAP⁴⁺). Stable complexes with GMP were found for cationic porphyrins, except for monocationic AB₃⁺. The binding constant (K_GMP  10⁴ M⁻¹) follows the order: A₃B³⁺  ABAB²⁺ > A₄⁴⁺  TMAP⁴⁺. Also, interaction with DNA was observed for all evaluated cationic porphyrins. For these related cationic porphyrins, the binding constant (K_DNA  10⁵ M⁻¹) increases with the number of cationic charges. On the other hand, the photodynamic activity of porphyrins was analyzed in solution of GMP and DNA. Monocationic AB₃⁺ is a less effective sensitizer to oxidize GMP in comparison with the other cationic porphyrins, in agreement with the lack of detected interaction with this nucleotide. The electrophoretic analysis of DNA indicates that photocleavage takes place when the samples are exposed to photoexcited tricationic and tetracationic porphyrins. In the presence of sodium azide the DNA decomposition was diminished. Also, reduction in the DNA photocleavage was observed under anoxic condition, indicating that oxygen is essential for DNA photocleavage sensitized by these cationic porphyrins. In addition, an increase in DNA degradation was not observed in deuteriated water. Therefore, an important contribution of type I photoreaction processes could be occurring in the DNA photodamage sensitized by these cationic porphyrins. These results provide a better understanding of the characteristics needed for sensitizers to produce efficient DNA photocleavage.     

Simultaneous determination of chloride, nitrate and sulphate in vegetable samples by single-column ion chromatography

A new ion chromatography method is described for the simultaneous determination of Cl⁻, NO₃⁻ and SO₄²⁻, using a selected eluent 1.3-mM sodium gluconate/1.3-mM borax (pH 8.5). The extraction methods of Cl⁻, NO₃⁻, SO₄²⁻ in vegetables are studied. The determination limits of Cl⁻, NO₃⁻, SO₄²⁻ are 0.17 μg/ml, 0.63 μg/ml and 0.81 μg/ml. The linear ranges are 060 μg/ml, 090 μg/ml and 090 μg/ml. The relative S.D. are <2.5%. The mean recoveries of Cl⁻, NO₃⁻, SO₄²⁻ in vegetables range from 97.0 to 104%.     

Characterization of a 10.3-μm pulsed DFB quantum cascade laser

We have measured the output parameters of a 10.3-μm pulsed distributed-feedback (DFB) quantum cascade (QC) laser manufactured by Alpes Lasers and intended for high-sensitivity detection of ammonia and ethylene. The laser beam was collimated with an AR-coated aspheric ZnSe lens with focal length of 11.6 mm and clear aperture of 16.5 mm. Near- and far-field distributions of the laser emission were recorded with an infrared imaging camera. The fast-and slow-axis laser beam divergences were measured to be 1.2 and 1.4 mrad (FWHM), respectively. The divergence was found to be increasing with injection current. An air-spaced Fabry–Perot interferometer with free spectral range of 0.05 cm⁻¹ was used to measure the frequency tuning rates of the laser. The laser was tuned by either heat sink temperature, injection current or pulse repetition rate with rates of −8 × 10⁻² cm⁻¹ K⁻¹, −7 × 10⁻² cm⁻¹ A⁻¹ and −9 × 10⁻⁴ cm⁻¹ kHz⁻¹, respectively. The laser frequency decreased linearly with a rate of 10⁻² cm⁻¹ ns⁻¹ (300 MHz ns⁻¹) for laser pulses varied from 10 to 50 ns, and the frequency chirp rate was found to decrease for longer laser pulses.     

Effect of small amount of poly(ethylene naphthalate) on isothermal crystallization and spherulitic morphology of poly(trimethylene terephthalate)

The effect of a small amount of poly(ethylene naphthalate) (PEN) in its blends with poly(trimethylene terephthalate) (PTT) on isothermal melt-crystallization kinetics and spherulitic morphology of the blends was thoroughly investigated. The maximum PEN content in the blends was 9 wt%. Due to the single composition-dependent glass transition temperature (T_g) that was observed for each blend, these blends appeared to be miscible in the amorphous state. After isothermal crystallization from the melt state, the neat PTT and its blends with PEN exhibited either double or triple melting endotherms. The triple endothermic peaks were observed in both the neat PTT and the blends when being crystallized at crystallization temperatures (T_c) of less than or equal to 195 °C. The equilibrium melting temperature () for the neat PTT was determined based on the linear Hoffman–Weeks extrapolative method to be 248 °C. Such values for the blends were found to decrease with the addition and increasing amount of PEN. Both the neat PTT and the blends were isothermally crystallized over the T_c range of 190–205 °C. At a given T_c, the 97PTT/3PEN blend exhibited a half-time of crystallization (t_0.5) value that was lower, while it exhibited reciprocal half-time (), Avrami rate constant (K_A), and spherulitic growth rate (G) values that were greater, than those of the neat PTT. With further increase in the PEN content, the t_0.5 value increased, while the , K_A, and G values decreased. Analysis of the G values based on the Lauritzen–Hoffman's (LH) secondary nucleation theory showed that the neat PTT and the 91PTT/9PEN blend exhibited a regime II→III transition at 194 °C (467.2 K), while no regime transition was observed for the other two blends. The lateral and the fold surface free energies (σ and σ_e) and the work of chain folding (q) for the neat PTT and the blends were 19.4, 30.2–46.3 erg cm⁻², and 2.4–3.6 kcal mol⁻¹, respectively. Lastly, the effect of both the T_c and the PEN content on morphology and texture of the PTT spherulites was also investigated and the results showed that the texture of the spherulites became coarser with increasing T_c and PEN content.     

Solvent effect on the blue shifted weakly H-bound F3 CH…FCD3 complex

Solvent effect on the ν^c frequency of CH stretching vibration of the blue shifted F₃CH…FCD₃ complex has been studied in liquefied N₂, CO, Ar, Kr and Xe. In the case of Xe, the spectroscopic measurements have also been extended to the solid state. It was found that the ν^c position of the complex in the solutions studied lowers with respect to the value in the gas phase. In liquid Xe, characterized by the largest permittivity, this effect reaches its maximum value of −14.5 cm⁻¹. The ν^c frequency begins to grow again just below the freezing point of Xe, where a noticeable (15%) increase of the density of Xe occurs. The experimental results obtained for the liquid phase have been analyzed in the framework of the Onsager-like reaction field model and Polarizable Continuum Model (PCM) implemented into a standard Gaussian 98 Program.     

Enhanced tungstate electrochromism via formation of transparent conductive networks

Indium tin oxide (ITO) nanopowder was added to a polymer film containing WO₃ · H₂O particles to enhance electron conductivity and complimentary Li ion kinetics in an electrochromic device. Film conductivity increased dramatically with ITO content, suggesting the formation of conductive ITO networks in the film. The improved electron conductivity leads to a substantial increase of the effective Li⁺ ion diffusion coefficient in the composite film, from 10⁻¹¹ to 10⁻⁹ cm²/s. Electrochromic contrast studies revealed that the presence of the ITO networks leads to enhanced blue/green color contrast.     

State to state rotational integral cross sections and rate coefficients of HCP collision with He at low temperature

We report coupled-cluster [CCSD(T)] ab initio calculations of the two-dimensional interaction potential energy surface of the HCP–He complex. The aug-cc-pVTZ and aug-cc-pVQZ gaussian basis sets are used. HCP is held fixed at its linear equilibrium ground vibrational level with the corresponding [H–C] and [C–P] bond lengths set to the values 2.016 bohrs and 2.914 bohrs, respectively. Our calculations are corrected for basis set superposition errors (BSSE). The PES obtained with the above triple zeta basis set has two minima located 22.018 cm⁻¹ and 14.808 cm⁻¹ below the HCP+He dissociation limit. These well depths are shifted to 23.505 cm⁻¹ and 15.949 cm⁻¹, respectively, when the quadruple zeta basis set is used. Our PESs are fitted on a basis of Legendre polynomial functions and state to state rotational integral cross sections of the HCP collision with He are calculated in the close-coupling (CC) approximation. Downward rate coefficients are inferred at low temperature () by averaging the cross sections over a Maxwell–Boltzmann velocity distribution. An analysis of our results shows that for kinetic energies greater than 60 cm⁻¹, the 0→2 transition dominates. The numbers derived here may be very useful for astrophysical observations.     

Langmuir monolayers and Langmuir–Blodgett films of 1-acyl-1,2,4-triazoles

New 1-acyl-1,2,4-triazoles (ATs) with different n-alkyl chain lengths from C2 to C18 were synthesized. ATs with long n-alkyl chains (C12 and larger) are non-charged amphiphilic molecules with a polar triazole head group. The Langmuir isotherms of ATs at the air–water interface with 12 (DoT-C12), 14 (MyT-C14), 16 (PaT-C16) and 18 (StT-C18) carbon atoms in their n-alkyl chains were studied using surface pressure-mean molecular area (π-mmA) measurements. Characteristic for the Langmuir isotherms of PaT-C16 and StT-C-18 was the first sharp increase of the surface pressure at a mmA value of 20 Å² marking a transition of the ATs from the gaseous state with n-alkyl chains already oriented perpendicular to the water surface to a condensed state. The collapse of the monolayers occurred between 20 and 36 mN m⁻¹ with a typical ‘spike’ in the isotherms of MyT-C14, PaT-C16 and StT-C18 which can be assigned to the buckling and subsequent folding of the monolayer. After the collapse point a pseudo-plateau region of slightly increasing surface pressure appeared for all ATs from C12 to C18 indicating a trilayer formation by the roll-over mechanism for MyT-C14, PaT-C16 and StT-C18. Upon further compression the final collapse occurred at π values between 59 and 67 mN m⁻¹. From reversibility studies it was found that the Langmuir isotherms of the ATs were irreversible. The morphology of Langmuir–Blodgett films of ATs transferred onto silicon wafers was studied by atomic force microscopy.     

High-accuracy determination of iron in seawater by isotope dilution multiple collector inductively coupled plasma mass spectrometry (ID-MC-ICP-MS) using nitrilotriacetic acid chelating resin for pre-concentration and matrix separation

In the present paper we describe a robust and simple method to measure dissolved iron (DFe) concentrations in seawater down to <0.1 nmol L⁻¹ level, by isotope dilution multiple collector inductively coupled plasma mass spectrometry (ID-MC-ICP-MS) using a ⁵⁴Fe spike and measuring the ⁵⁷Fe/⁵⁴Fe ratio. The method provides for a pre-concentration step (100:1) by micro-columns filled with the resin NTA Superflow of 50 mL seawater samples acidified to pH 1.9. NTA Superflow is demonstrated to quantitatively extract Fe from acidified seawater samples at this pH. Blanks are kept low (grand mean 0.045 ± 0.020 nmol L⁻¹, n = 21, 3× S.D. limit of detection per session 0.020–0.069 nmol L⁻¹ range), as no buffer is required to adjust the sample pH for optimal extraction, and no other reagents are needed than ultrapure nitric acid, 12 mM H₂O₂, and acidified (pH 1.9) ultra-high purity (UHP) water. We measured SAFe (sampling and analysis of Fe) reference seawater samples Surface-1 (0.097 ± 0.043 nmol L⁻¹) and Deep-2 (0.91 ± 0.17 nmol L⁻¹) and obtained results that were in excellent agreement with their DFe consensus values: 0.118 ± 0.028 nmol L⁻¹ (n = 7) for Surface-1 and 0.932 ± 0.059 nmol L⁻¹ (n = 9) for Deep-2. We also present a vertical DFe profile from the western Weddell Sea collected during the Ice Station Polarstern (ISPOL) ice drift experiment (ANT XXII-2, RV Polarstern) in November 2004–January 2005. The profile shows near-surface DFe concentrations of 0.6 nmol L⁻¹ and bottom water enrichment up to 23 nmol L⁻¹ DFe.     

An investigation of the chemiluminescence reaction in the sodium hypochlorite–folic acid–emicarbazide hydrochloride system

A chemiluminescence method for the determination of folic acid by the sodium hypochlorite–folic acid–semicarbazide hydrochloride system with a new flow injection technique has been established. The new method can perform simple, sensitive and rapid determinations of folic acid. The response to the concentration of folic acid, in the range of 1.0×10⁻⁷5.0×10⁻⁵ g/ml, is linear. The relative standard deviation of the method is 2.3% (C_s=4.0×10⁻⁶ g/ml, n=11). The detection limit is 2.7×10⁻⁸ g/ml. This method is suitable for automatic and continuous analysis, and has been successfully tested for the determination of folic acid in a folic acid tablet.     

Photoacoustic infrared spectroscopy of polymer beads

Photoacoustic (PA) spectra of four types of polymer resin beads, ranging in size from 35 to 150 μm, were acquired using a Fourier transform infrared spectrometer capable of both rapid- and step-scan mirror movement. Thermal diffusion lengths were on the order of the particle sizes of the beads. The PA magnitude spectra were similar to absorption spectra; both positive- and negative-going features occurred in the phase spectra. The frequency dependences of the total PA intensities of the polymer resins and carbon black differed by a factor of about f^−0.30. The intensities of the weak bands in the ratioed spectra (resin beads/carbon black) displayed a similar dependence. Partial saturation caused a more gradual variation for the stronger bands, where the intensity is proportional to f^−0.1–f^−0.2.     

Charge transport modulation of silicon nanowire by O2 plasma

The modification of the electrical characteristics of field-effect transistors (FETs) with channels composed of n- or p-type silicon nanowires (SiNWs) by oxygen plasma treatment is investigated in this study. The SiNWs obtained from silicon bulk wafers are <111> surface-oriented and their doping concentrations are 10²¹ and 10¹⁷ cm⁻³ for the n- and p-type SiNWs, respectively. After the back-gate SiNWFETs were subjected to oxygen plasma treatment, the magnitude of the drain current of the n-type SiNWs was decreased, whereas that of the p-type SiNWs was increased, while the gate-dependent characteristics of both of types of SiNWs were improved. The changes in the electrical characteristics are due to the adsorption of oxygen ions on the surface of the SiNWs. To verify the effect of the oxygen ions, the SiNWFETs were kept in a vacuum for 24 h whereupon their electrical characteristics tended to revert to their inherent state.     

Molecular fine structure and transition dipole moment of NO2 using an external cavity quantum cascade laser

Rotational vibrational fine structure and transition dipole moment of NO₂ is measured using Doppler free saturation spectroscopy with an external grating cavity quantum cascade laser (QCL). The QCL wavelength is calibrated using a 310 cm long internally coupled Fabry–Perot interferometer. We obtain a frequency splitting of 139.68 ± 0.06 MHz (0.0047 cm⁻¹) between the spin doublets (17) of 000 → 001 transition of NO₂. The resolution of the QCL based saturation spectrometer is limited by the QCL linewidth of 3.99 MHz ( 0.00013 cm⁻¹) deduced from the half width of the Lamb dips. The Lamb dip spectroscopy is utilized to obtain a vibrational dipole moment of 0.37 Debye for the (17) transitions.