Determination of the Solubility Parameter of Epoxidized Soybean Oil by Inverse Gas Chromatography

The thermodynamic parameters of epoxidized soybean oil (ESO) were determined by means of inverse gas chromatography (IGC) in the temperature range of 303.15 K-343.15 K. Two groups of probe solvents with different chemical natures and polarities were used to obtain information about ESO. The thermodynamic parameters—such as molar heat of sorption, weight fraction activity coefficient, Flory–Huggins interaction parameter, and partial molar heat of mixing—were obtained to judge the interactions between ESO and solvents at the studied temperatures. Also, the solubility parameters of ESO were found by plotting the graph of δ₁ ²/(RT) – χ^∞ ₁₂/V₁ vs. solubility parameters, δ₁, of the probes. The results showed that the selected solvent ethyl acetate was a moderate solvent for ESO; n-hexane was a moderate (but close to a better) solvent; while the probes n-heptane, n-octane, n-nonane, and chloroform were excellent solvents. From the extrapolation to 298 K, the solubility parameter value of ESO was 16.70 (J/cm³)^0.5.     

Reactivity of hydrogen peroxide with respect to ozone

Ozone decomposition in pure water, H₂O₂ aqueous solution, and water with ethanol admixture is investigated. It is found that, in the presence of H₂O₂, ozone decomposes significantly faster than in pure water owing to its interaction with H₂O₂. The effective rate constant (k = (0.023 ± 0.002) l/(mol s)) is determined, which is much higher than the overall rate constant of ozone decomposition in water, but much lower than the specific rate of ozone decomposition in water in the presence of common organic admixtures (fulvic acids, ethanol). It is concluded that at the combined use of O₃ and H₂O₂ for the decomposition of organic admixtures in water, the contribution of their interaction with each other is little.     

Small Molecule Sorption and Desorption in and Out of Iota‐Carrageenan Gels

Small molecule sorption and desorption in and out of Iota‐Carrageenan was studied by using steady‐state fluorescence (SSF) technique. Pyranine dissolved in water used as fluorescence probe. Fluorescence emission intensity, I _p from pyranine was monitored for studying sorption and desorption processes at various temperatures. The Fickian model was applied to produce sorption, D_s, early desorption, D_ed, and desorption, D_d, coefficients. Corresponding activation energies were obtained and found to be 20.5 kJ mol^?1, 7.0 kJ mol^?1 and 34.9 kJ mol^?1, respectively. The observed D_ed value is an order of magnitude smaller than the D_s and D_d coefficients. On the other hand, sorption processes were shown to be twice as fast as desorption processes.     

Kinetics study of a Diels‐Alder reaction in mixtures of an ionic liquid with molecular solvents

The second‐order rate constants for cycloaddition reaction of cyclopentadiene with naphthoquinone were determined spectrophotometrically in various compositions of 1‐(1‐butyl)‐3‐methylimidazolium terafluoroborate ([bmim]BF₄) with water and methanol at 25 °C. Rate constants of the reaction in pure solvents are in the order of water > [bmim]BF₄ > methanol. Rate constants of the reaction decrease sharply with mole fraction of the ionic liquid in aqueous solutions and increase slightly to a maximum in alcoholic mixtures. Multi‐parameter correlation of logk₂ versus solute–solvent interaction parameters demonstrated that solvophobicity parameter (Sp), hydrogen‐bond donor acidity (α) and hydrogen‐bond acceptor basicity (β) of media are the main factors influencing the reaction rate constant. The proposed three‐parameter model shows that the reaction rate constant increases with Sp, α and β parameters. Copyright © 2008 John Wiley & Sons, Ltd.     

Photoelectric fields in lithium niobate crystals

Photovoltaic and diffusion fields in nominally pure single crystals of stoichiometric composition (R = Li/Nb = 1) grown in the presence of 6 wt% K₂O flux (LiNbO₃ stoich. K₂O) in nominally pure single crystals of complementary composition (LiNbO₃), complementary single crystals doped with Zn²⁺, Er³⁺ at wavelength of 476, 514.5, 530 nm are defined according to parameters of photo induced light scattering indicatrix. Photo induced changes of crystals’ refractive index are defined.     

Heat transfer and Marangoni flow in a circular heat pipe using self-rewetting fluids

In this study, Marangoni flow and heat transfer enhancement in a heat pipe have been investigated. The experiments were carried out at different heat inputs. A constant temperature water bath was used at the condenser section at three temperature levels. Heat transfer coefficients and thermal resistances of the heat pipe were measured for pure water and water/butanol solutions. The experimental results confirmed that the heat pipe filled with butanol solutions showed better thermal performance than the water-filled heat pipe. At maximum heat flux, 25% heat transfer improvement was obtained when 7 wt% butanol solution was used instead of pure water.     

Influence of sintering temperature on properties of BNKLLT–6 wt% BCTZ binary lead-free piezoelectric ceramic prepared through the solid-state combustion technique

In this work, a new binary 94 wt%[Bi_0.5(Na_0.68K_0.22Li_0.1)_0.5TiO₃ + 0.10 wt% of La₂O₃]–6 wt% [(Ba_0.85Ca_0.15)(Ti_0.90Zr_0.10)O₃] [BNKLLT–6 wt% BCTZ] ceramic was fabricated by the solid-state combustion technique and glycine was used as the fuel. The effect of sintering temperature in the range of 1075–1175 °C for 2 h on phase evolution, microstructure and electrical properties was investigated. The phase formation exhibited a coexistence structure between rhombohedral and tetragonal at low sintering temperature. As the sintering temperature increased, the phase formation changed to pseudo-cubic phase. The average grain size of the ceramics was increased with the increasing sintering temperature. Density, ?_r, ?_SA and T_FA of BNKLLT–6 wt% BCTZ ceramics increased while the T_SA decreased when the sintering temperature increased up to 1125 °C, while after this temperature the opposite trends occurred. At a sintering temperature of 1125 °C, the BNKLLT-6 wt% BCTZ sample showed the highest theoretical density (95.8%), maximum dielectric constant ?_SA (5278), highest d₃₃ (227 pC/N) and fair ferroelectric properties (P_r = 24.5 µC/cm² and E_c = 15.45 kV/cm).     

Understanding the high temperature oxidation and ignition behaviour of two-phase Mg–Nd alloys and a comparison to single phase Mg–Nd

The oxidation kinetics and the mechanism of two-phase Mg–Nd alloys were investigated via isothermal heating experiments conducted in dry air at 500 °C for 12 h. The oxidation kinetic curves reveal improved oxidation resistance on neodymium (Nd)-containing alloys compared to pure Mg. A lower mass gain was detected at 2.5-%Nd than at 6-Nd%, which was related to the lower amount of intermetallic phase on the alloy surface. The intermetallic phase has a significant effect on the oxide growth stage. Nd₂O₃ formation on the intermetallic phases creates diffusion paths for oxygen to the metal/oxide interface, affecting both the oxidation kinetics and the oxidation resistance of the alloys. The formation of a Nd-depleted region at the subsurface due to extensive Nd oxidation at the oxide/intermetallic interface lowers the protective ability of the oxide scale. As increasing the Nd content of binary Mg–Nd alloys above 0.5 wt% shifts the alloys from single-phase region to two-phase region, it adversely affects the ignition resistance.     

Influence of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript> on dielectric and barrier properties of polymer

Polymer composite comprising polyvinylidene fluoride (PVDF) and potassium hexatitante (K₂Ti₆O₁₃) was synthesized by solution casting. The effect of K₂Ti₆O₁₃ on surface, thermal, and electrical properties of polymer composite were investigated. The addition of K₂Ti₆O₁₃ with polymer leads to thermal degradation and transition of polymer composite from semi-crystalline to amorphous phase. The optimum results of contact angle for different loading wt% of K₂Ti₆O₁₃ were directly correlated with the surface morphology. Our experimental results confirmed the incorporation of K₂Ti₆O₁₃ in polymer by SEM micrographs. The evaluated dielectric properties (ε' = 424; tan δ = 2.14 at 130 °C and 100 Hz frequency for 20 wt% loading of K₂Ti₆O₁₃) for polymer composite are higher in compared to pure polymer. The enhancement in dielectric constant and changing the surface properties of polymer composite can be used for the development of electrochemical storage device applications.     

Miscibility and Crystallization Behavior of Poly (Ethylene Terephthalate)/Phosphate Glass Hybrids

Fundamental studies on miscibility and crystallization behavior of poly (ethylene terephthalate) (PET) and inorganic phosphate glass (Pglass) hybrids were conducted. The Flory–Huggins interaction parameter (χ) value of ?0.075 for the PET/Pglass hybrids was obtained using the Nishi–Wang equation, demonstrating that the Pglass and PET components were miscible in the melt state. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the phase separation occurred during quenching from the melt. The phase boundaries between PET and Pglass were blurred, which indicated partial compatibility of the components in the solid state. Contact angle measurements indicated the interfacial tension of PET/Pglass hybrids was 1.5 mN/m, and the work of adhesion was 78.0 mN/m at 28 °C. Based on the Hoffman–Lauritzen theory, the nucleation constant (K_g) and fold surface free energy (σ_e) of PET/Pglass hybrids were less than those of neat PET.     

Preparation and characterization of biodegradable poly(ε-caprolactone)-based gel polymer electrolyte films

Biodegradable polymer electrolyte films based on poly(ε-caprolactone) (PCL) in conjunction with lithium tetrafluoroborate (LiBF₄) salt and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄) ionic liquid were prepared by solution cast technique. The structural, morphological, thermal, and electrical properties of these films were examined using X-ray diffraction (XRD), optical microscopy (OM), differential scanning calorimetry (DSC), and impedance spectroscopy. The XRD and OM results reveal that the pure PCL possesses a semi-crystalline nature and its degree of crystallinity decreases with the addition of LiBF₄ salt and EMIMBF₄ ionic liquid. DSC analysis indicates that the melting temperature and enthalpy are apparently lower for the 40 wt% EMIMBF₄ gel polymer electrolyte as compared with the others. The ambient temperature electrical conductivity increases with increasing EMIMBF₄ concentration and reaches a high value of ～2.83?×?10^?4 S cm^?1 for the 85 PCL:15 LiBF₄ + 40 wt% EMIMBF₄ gel polymer electrolyte. The dielectric constant and ionic conductivity follow the same trend with increasing EMIMBF₄ concentration. The dominant conducting species in the 40 wt% EMIMBF₄ gel polymer electrolyte determined by Wagner’s polarization technique are ions. The ionic conductivity of this polymer electrolyte (～2.83?×?10^?4 S cm^?1) should be high enough for practical applications.     

Solvent and surfactant effect on the self-assembly and luminescence properties of ZrO2:Eu3+ nanoparticles

ZrO₂:Eu³⁺ nanocrystals ranging from 17 to 43 nm were prepared by the facile precipitation method with a hydrothermal process. The crystallite size was strongly influenced by the solvent composition and enhanced with the presence of surfactant. The use of ethanol combined with surfactant stabilizes 50 wt% of the monoclinic phase, while the use of water only results in 100 wt% tetragonal phase. 80% of nanobelts were obtained preparing the sample with ethanol and surfactant as a results of the self-assembly of nanoparticles. The photoluminescence emission peak centered at 606 nm dominates the emission band for nanobelts, while for nanoparticles it is dominated by a peak centered at 612 nm. Such differences were explained in terms of the site symmetry occupying Eu³⁺ in the host that in turn depends on the crystalline phase. Changes in the intensity ratio I(612 nm)/I(606 nm) is proposed as a tool to analyzing changes in the monoclinic/tetragonal phase composition. The calculated asymmetry ratio R=⁷F₂/⁷F₁～1.2 suggest a high degree of crystallinity of the prepared samples.     

Fluorescence and Nonlinear Optical Properties of Alizarin Red S in Solvents and Droplet

The enhancement of the nonlinear properties of materials is an interesting topic since it has many applications in optical devices and medicines. The Z-scan technique was used to study the values of the two-photon absorption (β), second-order molecular hyperpolarizability (γ_R), third-order susceptibility (χ_R), and nonlinear refractive index (n₂) of Alizarin Red S in different media using a continuous-wave diode-pump laser radiation at 532 nm. For Alizarin Red S in a droplet, the β, n₂, χ_R, and γ_R were estimated at the order of 10^?7 cm²/W and 10^?12 cm/W, 10^?3 m³ W^?1 s^?1 and 10^?24 m⁶ W^?1 s^?1, respectively. The results indicated that the values of β and n₂ reduced, whereas the values of χ_R and γ_R were enhanced when the solvent was changed from droplet to water, DMF, and dimethyl sulfoxide due to the change in the solvent’s dielectric constant (ε). Moreover, the values of β were enhanced by an increase in the concentration of the surfactant in the aqueous solution. The absorption spectra of Alizarin Red S in the aqueous solution was observed at 428 nm, and a few red shifts in the absorption spectra were observed with a reduction in the dielectric constant of the medium. The same effect was observed in the absorption spectra of Alizarin Red S in the droplet when the bulk dielectric constant reduced. The dielectric constant can affect the fluorescence spectra of Alizarin Red S when the solution is changed from water to dimethyl sulfoxide. The dipole moments of Alizarin Red S in the different media were studied using the quantum perturbation theory.     

Green luminescence and EPR studies on Mn-activated yttrium aluminum garnet phosphor

Yttrium aluminum garnet (Y₃Al₅O₁₂) and Mn activated Y₃Al₅O₁₂ phosphors have been prepared by urea combustion route in less than 5 min. The phosphors are well characterized by powder X-ray diffraction, Scanning electron microscopy and Fourier-transform infrared spectroscopic techniques. Photoluminescence tests on the pure Y₃Al₅O₁₂ showed a strong green emission at 525 nm (2.36 eV) attributed to the strongly allowed transition of F⁺ center whereas in Mn²⁺ activated YAG the green emission at 519 nm is due to the ⁴T₁ (G)→⁶A₁ (S) transition of Mn²⁺ ions. EPR studies have been carried out on Mn²⁺ activated Y₃Al₅O₁₂ phosphor at 300 and 110 K. From EPR spectra the spin-Hamiltonian parameters have been evaluated. The magnitude of the hyperfine splitting (A) indicates that the Mn²⁺ ions are in a moderately ionic environment. The spin concentration (N) and paramagnetic susceptibility (χ) have been evaluated and discussed.     

High-rate Li4Ti5O12/C composites as anode for lithium-ion batteries

The Li₄Ti₅O₁₂/C composites were synthesized by a simple solid-state reaction at 800 °C for 12 h by using Super P® conductive carbon black as carbon source. X-ray diffraction analysis shows that the Li₄Ti₅O₁₂ with 0, 5, 7.5, and 10 wt% carbon shows similar patterns with cubic spinel structure. Scanning electron microscope shows that Li₄Ti₅O₁₂ aggregated seriously, but the aggregation was inhibited by the addition of Super P® carbon. The results indicate that the addition of 5 wt% carbon during sintering and a further 5 wt% carbon during slurry preparation shows the best rate capability of 110 mAh/g when the cells were charge/discharged at 10 C rate. The comparison of the charge–discharge curves shows that the higher rate improvement should further decrease the particle size of LTO or improve the conductivity of LTO itself.     

Investigation on Three-Dimensional Solubility Parameters for Explanation and Prediction of Swelling Degree of Polydimethylsiloxane Pervaporation Membranes

Using polydimethylsiloxane (PDMS) as a basic matrix to prepare ethanol and butanol permselective pervaporation membranes is a vibrant field. Many studies have verified that the three-dimensional Hansen solubility parameters (HSP) theory offers a valid explanation for the swelling performance of ethanol and butanol in PDMS. Five parameters (δ_D, δ_P, δ_H, δ_t, and R_a) are defined in HSP theory which can be individually used to explain the interaction strength between a solvent and a polymer. However, for the above five parameters, which one is the most effective parameter for deciding the swelling degree still needs to be determined. In this study, a commonly used hydroxy-terminated PDMS precursor was adopted to prepare the PDMS network. The HSP of the chosen PDMS precursor was measured by an advanced “solubility-rating” method. The special software package HSPiP (4.1.03), purchased from the HSPiP team, was used to process the “solubility-rating” results. The equilibrium swelling degree (Q value) of the PDMS network in water, ethanol, butanol, and toluene was measured and the relationships between the five HSP parameters of the solvents and the logarithmic equilibrium swelling degree, log(Q), were discussed. It was found that the measured polar parameter, δ_P, of PDMS was 0.12 MPa^0.5. The measured hydrogen bonding parameter, δ_H, was larger than δ_P, attaining a value of 8.6 MPa^0.5, because the hydroxy groups directly contributed to the hydrogen bonding solubility parameter, δ_H. With respect to the relationships between log(Q) and δ_D, δ_P, δ_H, δ_t, and R_a, linear relationships existed after plotting log(Q) vs. δ_P and log(Q) vs. δ_H. The linear relation degree of the fitted lines was 0.995 and 0.989, respectively. Their standard deviations were 0.149 and 0.232, respectively. Therefore, a better linear relationship existed between log(Q) and δ_P than the other solubility parameters. This indicated that the polar interaction was the main effect for deciding the swelling degree of the PDMS network in water and alcohol systems.     

Thickness dependent optical dispersion parameters and nonlinear optical properties of nanostructured Cr doped CdO thin films

Cr doped CdO thin films were deposited on glass substrates by reactive DC magnetron sputtering with varying film thickness from 250 to 400 nm. XRD studies reveal that the films exhibit cubic structure with preferred orientation along the (2 0 0) plane. The optical transmittance of the films decreases from 92 to 72%, whereas the optical energy band gap of the films decreased from 2.88 to 2.78 eV with increasing film thickness. The Wemple–DiDomenico single oscillator model has been used to evaluate the optical dispersion parameters such as dispersion energy (E_d), oscillator energy (E_o), static refractive index (n_o) and high frequency dielectric constant (ε_∞). The nonlinear optical parameters such as optical susceptibility (χ⁽¹⁾), third order nonlinear optical susceptibility (χ⁽³⁾) and nonlinear refractive index (n₂) of the films were also determined.     

Sorption of Organic Solvents in Poly(Dimethyl Siloxane) Membrane. II. Effect of Sorption on the Polymer Crystals upon Cooling

Polymer crystalline properties in poly(dimethyl siloxane) (PDMS) film after solvation by various solvents was determined using low temperature differential scanning calorimetry (DSC). At various solvent uptake levels, the crystalline thermal properties of the solvated polymer were modified to different extents as revealed by the shifts in crystalline melting point (T_m) and its enthalpy (ΔH_m). Water uptake in PDMS was very limited (<0.01 g/g) and T_m did not significantly change during the sorption process. For toluene and cyclohexane penetrants, T_m moved toward a much lower temperature depending on the sorption levels. At low solvent uptakes, the T_m values decreased linearly with solvent uptakes due to formation of a miscible phase. Beyond a threshold, the T_m remained stable and an additional penetrant fusion peak appeared, implying the onset of a microphase separation phenomenon. The ΔH_m values for the swollen membranes were decreased, with the exception of the water penetrant. This indicates that a lower percentage of polymer chains were involved in the crystalline domain for swollen PDMS.