Spectroscopic Characterization of Miniaturized Atmospheric-Pressure dc Glow Discharge Generated in Contact with Flowing Small Size Liquid Cathode

The miniaturized atmospheric pressure glow discharge (APGD) generated between a solid electrode and a flowing small size liquid cathode (dimension 2 mm) was investigated here using optical emission spectroscopy. The discharge was studied in an open air atmosphere, and the spectral characteristics of the plasma source was examined. Analysed APGD was operated at a discharge voltage of 1,100–1,700 V, a discharge current of 20 mA and gaps between a solid anode and a liquid cathode in the range from 0.5 to 3.5 mm. The emission intensities of the main species were measured as a function of various experimental conditions, including the solution flow rate, the gap between the electrodes, and the concentration of hydrochloric acid. The excitation temperature, the vibrational temperatures calculated from N₂, OH, and NO bands, and the rotational temperatures determined from band of OH, N₂ and NO, were found to be dependent on these experimental parameters. The electron number density was determined from the Stark broadening of H_β line. Additionally, the ionization temperature and degree were calculated using the Saha–Boltzmann equation, with the ion to atom ratio for magnesium (MgII/MgI). The results demonstrated that T _exc(H), T _vib(N₂), T _vib(OH), T _vib(NO) and T _rot(OH) were well comparable (~3,800–4,200 K) for selected plasma generation conditions (gap ≥2.5 mm, HCl concentration ≥0.1 mol L⁻¹), while the rotational temperatures determined from band of N₂ (~1,700–2,100 K) and band of NO (~3,000 K) were considerably lower. The electron number density was evaluated to be (3.4–6.8) × 10²⁰ m⁻³ and the ionization temperature varied, throughout in the 4,900–5,200 K range.     

The use of different plasma gases (Ar, N 2 and air) for CMP-OES: figures of merit and temperature measurements

A comparative study of a 600 W capacitively coupled microwave plasma (CMP) operated with different plasma gases (Ar, N₂ and air) with respect to the achieved detection limits for Fe, Cr, Zn, Ca and Mg have been carried out. Radially and axially resolved rotational temperatures (T_rot), excitation temperatures (T_exc) and electron number densities (n_e) of these plasmas have been determined using OH (T_rot), Fe (T_exc) and Mg (n_e) as thermometric species. The influence of different gas flow rates on T_rot, T_exc and n_e, and of Li as an easily ionized element on T_exc has been investigated.     

Physical and analytical characteristics of an atmospheric pressure argon–helium radiofrequency capacitively coupled plasma

A very low power radiofrequency capacitively coupled plasma (13.56 MHz, 5–70 W), was generated in our laboratory on a sharp Kanthal tip without any counter electrode, as an intrinsic part of RLC series resonant circuit. Physical characteristics of this plasma obtained in Ar–He mixture, were studied as function of observation height or gas mixture composition. The excitation temperature of Ar (1500–2100 K), He (3000–3500 K) and H (2500–3200 K), the rotational temperature of the OH band (1300–2900 K), the electron temperature (5500–6500 K) and the electron number density (8 · 10¹³–2 · 10¹⁴ cm^− 3) were determined. The evolution of several atomic emission lines or molecular bands was studied in order to investigate the fundamental processes that take place in such plasma. From the point of view of analytical applications it was found that the optimum conditions of excitation (most intense emission lines and lowest detection limits) are met for a 42% He in the gas mixture and an observation height of 1 mm above the electrode. The optimum atomic emission analysis parameters were established for 7 elements (Na, Li, Ca, K, Cd, Zn and Hg) using pneumatically nebulized liquid solutions. It was found that the presence of He in the plasmogenic gas has an enhancing effect on the emission intensities and detection limits.     

Comparison of the Plasma Temperature and Electron Number Density of the Pulsed Electrolyte Cathode Atmospheric Pressure Discharge and the Direct Current Solution Cathode Glow Discharge

A novel-pulsed electrolyte cathode atmospheric pressure discharge (pulsed-ECAD) plasma source driven by an alternating current (AC) power supply coupled with a high-voltage diode was generated under normal atmospheric pressure between a metal electrode and a small-sized flowing liquid cathode. The spatial distributions of the excitation, vibrational, and rotational plasma temperatures of the pulsed-ECAD were investigated. The electron excitation temperature of H T_exc(H), vibrational temperature of N₂ T_vib(N₂), and rotational temperature of OH T_rot(OH) were from 4900?±?36 to 6800?±?108 K, from 4600?±?86 to 5800?±?100 K, and from 1050?±?20 to 1140?±?10 K, respectively. The temperature characteristics of the dc solution cathode glow discharge (dc-SCGD) were also studied for the comparison with the pulsed-ECAD. The effects of operating parameters, including the discharge voltage and discharge frequency, on the plasma temperatures were investigated. The electron number densities determined in the discharge system and dc-SCGD were 3.8–18.9?×?10¹⁴?cm^–3 and 2.6?×?10¹⁴ to 17.2?×?10¹⁴?cm^–3, respectively.     

Thermodynamic study of the n-octane-1-pentanol-sodium dodecyl sulfate solutions in water

The thermodynamic properties, PVTx (T_S, P_S, ρ_S), (∂P/∂T)_VX, and C_VVTx, of three microemulsions (water + n-octane + sodium dodecylsulfate + 1-pentanol) with composition of solution-1: 0.0777 (H₂O):0.6997 (n-C₈H₁₈):0.0777 (SDS):0.1449 (1-C₅H₁₁OH) mass fraction; solution-2: 0.6220 (H₂O):0.1555 (n-C₈H₁₈):0.0777 (SDS):0.1448 (1-C₅H₁₁OH) mass fraction; and solution-3: 0.2720 (H₂O):0.5054 (n-C₈H₁₈):0.0777 (SDS):0.1449 (1-C₅H₁₁OH) mass fraction were measured. Sodium dodecylsulfate (SDS) was used as an ionic surfactant, 1-pentanol used as stabilizer (cosurfactant), and n-octane as oil component in aqueous solution. A high-temperature, high-pressure, adiabatic, and nearly constant-volume calorimeter supplemented by quasi-static thermogram technique was used for the measurements. Measurements were made at eight densities (isochores) between 475.87 and 919.03 kg m⁻³. The range of temperature was from 275 to 536 K and pressure range was up to 138 bar. Uncertainty of the pressure, density, derivative (∂P/∂T)_VX, and heat capacity measurements are estimated to be 0.25%, 0.02%, 0.12-1.5%, and 2.5%, respectively. Temperatures at liquid-gas phase transition curve, T_S(ρ), for each measured densities (isochores) were determined using a quasi-static thermogram technique. The uncertainty of the phase transition temperature measurements is about ±0.02 K. The effect of temperature, density, and concentration on the heat capacity of the microemulsions is discussed. Along the isochore of 438.40 kg m⁻³ at temperatures above 525.44 K for the first solution the precipitation of the solid phase (SDS) was found.     

Reducing the formation of six-membered ring ester during thermal degradation of biodegradable PHBV to enhance its thermal stability

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) has attracted the attention of academia and industry because of its biodegradability, biocompatibility, thermoplasticity and plastic-like properties. However, PHBV is unstable above 160 °C during melt processing at a temperature above the melting temperature, which restricts practical applications as a commodity material. It is widely believed that thermal degradation of PHBV occurs almost exclusively via a random chain scission mechanism involving a six-membered ring transition state. Here, 2,2′-bis(2-oxazoline) (BOX) was selected to modify PHBV to control the formation of six-membered ring ester during thermal degradation. The resulting hydroxyl-terminated PHBVs (HT-PHBVs) had improved thermal stability due to a decrease in the negative inductive effect of the neighboring group of methylene groups at the β-position to the ester oxygen, and a decrease in the electron-denoting effect of substituent group of carbon atoms at α-position to the ester oxygen. The optimal reaction temperature and time were determined to be 95 °C and 6 h, respectively. Compared with those of original PHBV, the temperature determined at 5% weight loss (T_5%), the initial decomposition temperature (T₀), the maximum decomposition temperature (T_max), the complete decomposition temperature (T_f) of HT-PHBV prepared under the optimal conditions increased by 31, 24, 19 and 19.1 °C, respectively.     

Study of poly(bisphenol A carbonate) relaxation kinetics at the glass transition temperature

In this work, the variations of the relaxation times are investigated above and below the glass transition temperature of a model amorphous polymer, the polycarbonate. Three different techniques (calorimetric, dielectric and thermostimulated currents) are used to achieve this goal. The relaxation time at the glass transition temperature was determined at the temperature dependence convergence of the relaxation times calculated with dynamic dielectric spectroscopy (DDS) for the liquid state and thermostimulated depolarisation currents (TSDC) for the vitreous state. We find a value of τ(T_g) = 110 s for PC samples. The knowledge of the temperature dependence, τ(T), and the value τ(T_g) enables to determine the glass-forming liquid fragility index, m. We find m = 178 ± 5.     

Synthesis of silsesquioxanes based in (3-methacryloxypropyl)-trimethoxysilane using methacrylate monomers as reactive solvents

The polycondensation of (3-methacryloxypropyl)-trimethoxysilane in acidic conditions using different methacrylate monomers as reactive solvents resulted in incompletely condensed methacrylate-functionalized silsesquioxanes with a very large fraction of intramolecular cycles. UV-MALDI-TOF-MS analysis demonstrated that the species present after 2 weeks of reaction at 60 °C were: T₆(OH)₂, T₇(OH), T₈(OH)₂, T₉(OH), T₁₀(OH)₂ and T₁₁(OH). Analysis of samples after 30 months of storage at room temperature revealed the presence of T₁₂(OH)₂ and T₁₃(OH) species. The absence of higher molar mass oligomers after prolonged storage periods is attributed to dilution of the reacting medium, which discourages bimolecular reactions that lead to polymer growth. ²⁹Si NMR spectroscopy showed that the conversion in the polycondensation reaction was in the range 0.91-0.96. The methacrylate monomers are not involved in the hydrolysis-condensation reactions with MPTMS and therefore can be polymerized by thermal or photochemical means, thereby cross-linking the preformed nanosized cagelike silsesquioxanes. The formulations containing silsesquioxanes showed a markedly reduced content of extractable monomer after photopolymerization, which makes these resins very attractive for dental filling materials.     

Atmospheric pressure,radio frequency,parallel plate capacitively coupled plasma—excitation temperatures and analytical figures of merit

Electronic excitation (T_exc) and rotational (T_rot) temperatures were determined for a parallel plate capacitively coupled rf plasma operating at atmospheric pressure. T_exc was calculated from the slope of the Boltzmann plot using Fe and He as the thermometric species and Pb excitation temperature was calculated using the two line method. Over a power range from 100 W to 250 W, excitation temperatures are 3255–3900 K for He, 3540–4500 K for Pb, and 4300–4890 K for Fe. The rotational temperature was measured using both OH and N₂⁺ molecular spectra and the values are in the range of 828–911 K and 845–956 K respectively over a power range of 75–275 W. Signal-to-noise ratios, signal-to-background ratios, and absolute detection limit for lead (0.33 ng) and silver (24 pg) are also reported.     

Metamagnetism in DyBaCo2O5+x, x≈0.5

The temperature dependence of the paramagnetic susceptibility χ_m(T) taken in 2500 Oe, the resistivity ρ(T), and the thermoelectric power α(T) of DyBaCo₂O_5+x, which has Ba and Dy ordered into alternate (001) planes of an oxygen-deficient perovskite, have revealed a phase segregation in the compositional range 0.3?x<0.5. Orthorhombic DyBaCo₂O_5.51 has, in addition, oxygen vacancies ordered into alternate rows of the DyO_0.51 (001) planes; a cold-pressed polycrystalline sample exhibits a first-order insulator-metal transition at T_IM=320 K, a Curie temperature T_C=300 K, and a broadened metamagnetic transition temperature T_M≈265 K in 2500 Oe. A ferromagnetic M-H hysteresis curve fails to saturate at 5 T, and a minority ferromagnetic phase below T_M has a volume fraction that decreases with decreasing temperature, vanishing below 50 K. Oxygen vacancies in the DyBaCo₂O_5.5 phase suppress the metallic state; interstitial oxygen does not. A thermoelectric power α(T)>0 of DyBaCo₂O_5.51 changing continuously across T_IM is interpreted to manifest a metallic minority phase crossing a percolation threshold; α(T) also provides evidence for a progressive excitation of higher-spin Co(III) with increasing temperature from below 50 K to above T_IM. A previous model of the RBaCo₂O_5.5 phase is extended to account for the Ising spin configuration below T_C, the magnetic order in the presence of higher-spin octahedral-site Co(III), and the α(T) data.     

Thermodynamic studies on SrFe12O19(s), SrFe2O4(s), Sr2Fe2O5(s) and Sr3Fe2O6(s)

The citrate-nitrate gel combustion route was used to prepare SrFe₂O₄(s), Sr₂Fe₂O₅(s) and Sr₃Fe₂O₆(s) powders and the compounds were characterized by X-ray diffraction analysis. Different solid-state electrochemical cells were used for the measurement of emf as a function of temperature from 970 to 1151 K. The standard molar Gibbs energies of formation of these ternary oxides were calculated as a function of temperature from the emf data and are represented as (SrFe₂O₄, s, T)/kJ mol⁻¹ (±1.7)=−1494.8+0.3754 (T/K) (970?T/K?1151). (Sr₂Fe₂O₅, s, T)/kJ mol⁻¹ (±3.0)=−2119.3+0.4461 (T/K) (970?T/K?1149). (Sr₃Fe₂O₆, s, T)/kJ mol⁻¹ (±7.3)=−2719.8+0.4974 (T/K) (969?T/K?1150).Standard molar heat capacities of these ternary oxides were determined from 310 to 820 K using a heat flux type differential scanning calorimeter (DSC). Based on second law analysis and using the thermodynamic database FactSage software, thermodynamic functions such as Δ_fH°(298.15 K), S°(298.15 K) S°(T), C_p°(T), H°(T), {H°(T)-H°(298.15 K)}, G°(T), free energy function (fef), Δ_fH°(T) and Δ_fG°(T) for these ternary oxides were also calculated from 298 to 1000 K.     

Thermodynamics of 2D polymerized tetragonal phase of fullerene C60 in the range from T→0 to 650 K at standard pressure

By dynamic calorimetry the temperature dependence of heat capacity for two-dimensional (2D) polymerized tetragonal phase of C₆₀ has been determined over the 300-650 K range at standard pressure mainly with an uncertainty ±1.5%. In the range 490-550 K, an irreversible endothermic transition of the phase, caused by the depolymerization of the polymer, has been found and characterized. Based on the experimental data obtained and literature information, the thermodynamic functions of 2D polymerized tetragonal phase of C₆₀, namely, the heat capacity C°_p(T), enthalpy H°(T)−H°(0), entropy S°(T), and Gibbs function G°(T)−H°(0), have been calculated over the range from T→0 to 490 K. From 150 to 330 K in an adiabatic vacuum calorimeter and between 330 and 650 K in a dynamic calorimeter the thermodynamic properties of the depolymerization products have been examined and compared with the corresponding data for the monomeric phase C₆₀.     

Study of the photophysical behavior of tetrasulfonated metallophthalocyanines in the presence of CdTe quantum dots

Förster resonance energy transfer (FRET) studies were carried out with CdTe quantum dots (QDs) synthesized in aqueous phase and various tetrasulfonated metallophthalocyanines (MPcS₄, M = aluminum ((OH)AlPcS₄), zinc (ZnPcS₄), silicon ((OH)₂SiPcS₄) and germanium ((OH)₂GePcS₄) in a H₂O:MeOH (1:1) solvent mixture. The QDs studied were capped with thioglycolic acid (TGA) or mercaptopropionic acid (MPA) with sizes ranging from 2.3 to 3.7 nm. Non-radiative energy transfer from QDs emission to MPcS₄ complexes was observed. Study of the photophysics of the MPcs in the presence of the QDs revealed high triplet state quantum yields (Φ_T, ranging from 0.41 to 0.85 in the presence of QDs), with corresponding long triplet state lifetimes (τ_T, which ranged from 140 to 610 μs in the presence of QDs) to allow for photosensitized reactions to occur. The efficiency of energy transfer and the donor–acceptor distance between the MPcs and the QDs were also evaluated.     

(27)Al NMR and Raman spectroscopic studies of alkaline aluminate solutions with extremely high caustic content - Does the octahedral species Al(OH)(6)(3-) exist in solution?

²⁷Al NMR and Raman spectra of alkaline aluminate solutions with 0.005 M ≤ [Al(III)]_T ≤ 3 M in various M′OH solutions (M′⁺ = Na⁺, K⁺ and Li⁺) were recorded and analysed. Caustic concentrations up to 20 M were used to explore whether higher aluminium hydroxo complexes are formed at extremely high concentrations of hydroxide. A single peak was observed on the ²⁷Al NMR spectrum of each solution. The chemical shift of this peak shifts significantly upfield with increasing [M′OH]_T in solutions with [Al(III)]_T < 0.8 M. This variation shows a strong dependence on the cation of the solution and practically disappears in systems with [Al(III)]_T ≥ 0.8 M. For Raman spectra of solutions with [Al(III)]_T = 0.8 M and [NaOH]_T ≥ 10 M, the peak maximum of the symmetric ν₁-AlO₄ stretching of Al(OH)₄⁻ shifted progressively from ∼620 to ∼625 cm⁻¹ and decreased in intensity with increasing [NaOH]_T. In parallel, modes centred at ∼720 and ∼555 cm⁻¹ (cf. ∼705 and ∼535 cm⁻¹ at lower [NaOH]_T, ascribed to a dimeric aluminate species appeared, and their intensities increased with increasing [NaOH]_T. These variations in the ²⁷Al NMR and Raman spectra can be interpreted in terms of contact ion-pairs formed between the cation of the medium and the well-established Al(OH)₄⁻ or the dimeric aluminate species. Assumption of higher aluminium hydroxo complex species (e.g., Al(OH)₆³⁻) is not necessary to explain the spectroscopic effects observed.     

Structural control of dithiazolyl radicals: Case studies on 3′- and 4′-cyano-benzo-1,3,2-dithiazolyl, NCC6H3S2N

Dithiazolyl radicals with π-stacking motifs have attracted particular interest because of their ability to exhibit spin-switching between diamagnetic distorted π-stacks and paramagnetic regular π-stacked structures through a solid state phase transition. Previous studies indicate that inclusion of electronegative heteroatoms into the backbone favours lamellar structures. This methodology has been extended to the synthesis and characterisation of the title compound, 4′-cyanobenzo-1,3,2-dithiazolyl (4-NCBDTA). Its electronic structure is probed through DFT calculations, cyclic voltammetry and EPR spectroscopy and its crystal structure determined by X-ray powder diffraction at room temperature. Variable temperature SQUID magnetometry reveals that 4-NCBDTA undergoes two phase transitions, each exhibiting bistability; a high temperature phase transition occurs at room temperature (T_C↓ = 291 K, T_C↑ = 304 K, ΔT = 13 K); whilst the low temperature phase transition occurs below liquid nitrogen temperatures (T_C↓ = 37 K, T_C↑ = 28 K;ΔT = 9 K).     

Electrical conductivity investigation of diluted potassium chloride solutions in binary mixture triethylamine-water near its consolute point

The binary liquid mixture of triethylamine + water (TEA-W) has a lower consolute point at a critical composition of 32.27 mass % triethylamine. Starting at a temperature within the one-phase region, the electrical conductivity of a sample of this mixture with addition of (K⁺, Cl⁻) ions was measured and found to be accurately described by the Vogel-Fulcher-Tammann (VFT) law. Before that, for the pure system, in a temperature range ΔT = T_c − T < 2 °C where T_c is the critical temperature, the electrical conductivity (σ) exhibits a monotonous deviation from the VFT behaviour. This anomaly is finite at T_c. The asymptotic behaviour of the electrical conductivity anomaly is described by a power law t^1−α, where t is the reduced temperature |(T−Tc)/Tc| and α is the critical exponent of the specific heat anomaly at constant pressure. For the electrolyte mixtures, by combining the viscosity and the electrical conductivity data, the value of the computed Walden product has been determined and the salt dissociation degrees as well as the Debye screening length have been estimated.     

Synthesis and characterization of crosslinkable polyimides

A series of copolyimides were prepared from benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (BTDA) and various aromatic diamines which contain a fluorenyl group and/or alkyl substituents in ortho position to the amine groups. The effect of the chemical composition on the glass transition temperature (T_g), thermal stability as well as on the dielectric constant of these polymers was studied. High T_g polymers (T_g ranging from 260 °C to 370 °C), withstanding temperatures as high as 400 °C for 10 h and having a low dielectric constant (from 2.6 to 3.1) were successfully synthesized. All these polymers were able to crosslink under UV or thermal treatments.     

Mercury thiocyanate coordination polymers generated from rigid or flexible organic nitrogen donor-based ligands

Four mercury(II) thiocyanate–organic polymeric complexes, [Hg(μ-4,4-bipy)(SCN)₂]_n (1), [Hg(μ-bpa)(SCN)₂]_n (2), [Hg(μ-bpe)(SCN)₂]_n (3), [Hg(μ-bpp)(SCN)₂]_n (4) {4,4-bipy = 4,4′-bipyridine, bpa = 1,2-bis(4-pyridyl)ethane, bpe = 1,2-bis(4-pyridyl)ethene and bpp = 1,3-di(4-pyridyl)propane} were prepared from reactions of mercury(II) thiocyanate with four rigid and flexible organic nitrogen donor-based ligands under thermal gradient conditions, brunched tube method. All these compounds were structurally determined by X-ray single-crystal diffraction. The thermal stabilities of compounds 1–4 were studied by thermal gravimetric (TG) and differential thermal analyses (DTA). Solid state luminescent spectra of compounds 1 and 3 indicate intense fluorescent emissions at 430 and 468 nm, respectively.     

Understanding the flowing atmospheric-pressure afterglow (FAPA) ambient ionization source through optical means

The advent of ambient desorption/ionization mass spectrometry (ADI-MS) has led to the development of a large number of atmospheric-pressure ionization sources. The largest group of such sources is based on electrical discharges; yet, the desorption and ionization processes that they employ remain largely uncharacterized. Here, the atmospheric-pressure glow discharge (APGD) and afterglow of a helium flowing atmospheric-pressure afterglow (FAPA) ionization source were examined by optical emission spectroscopy. Spatial emission profiles of species created in the APGD and afterglow were recorded under a variety of operating conditions, including discharge current, electrode polarity, and plasma-gas flow rate. From these studies, it was found that an appreciable amount of atmospheric H₂O vapor, N₂, and O₂ diffuses through the hole in the plate electrode into the discharge to become a major source of reagent ions in ADI-MS analyses. Spatially resolved plasma parameters, such as OH rotational temperature (T_rot) and electron number density (n_e), were also measured in the APGD. Maximum values for T_rot and n_e were found to be ~1100 K and ~4 × 10¹⁹ m^–3, respectively, and were both located at the pin cathode. In the afterglow, rotational temperatures from OH and N₂⁺ yielded drastically different values, with OH temperatures matching those obtained from infrared thermography measurements. The higher N₂⁺ temperature is believed to be caused by charge-transfer ionization of N₂ by He₂⁺. These findings are discussed in the context of previously reported ADI-MS analyses with the FAPA source.     

Thermal and rheological behaviour of some random aromatic polyethersulfone/polyetherethersulfone copolymers

The thermal and rheological behaviour of seven random Cl-ended aromatic PES/PEES copolymers (M_n ≈ 9500 g mol⁻¹), at various PES/PEES repeating unit ratios, was studied. The glass transition temperatures (T_g), determined by DSC experiments, showed a dependence on copolymer composition significantly different from the ideal linear behaviour expected on the basis of Fox equation. Degradations were carried out in the scanning mode, under flowing nitrogen, in the temperature range 35-650 °C and a single degradation stage was observed for all copolymers. The initial decomposition temperatures (T_i) and the half decomposition temperatures (T_1/2) were directly determined by TG curves, while the apparent activation energies of degradation (E_a) were obtained by the Kissinger method. In addition, the complex viscosity (η^∗) of molten copolymers was determined in experimental conditions of linear viscoelasticity. T_i, T_1/2, E_a, and η^∗ values were depending on copolymer composition, showing a trend similar to that of T_g values. The results obtained were discussed and interpreted.