Sodium Taurocholate-Induced Lamellar-Micellar Phase Transitions of DPPC

The thermotropic transitions of 1,2-dipalmitoylphosphatidylcholine (DPPC) and the structural changes of its lamellar phases have been studied between 0 and 50°C by both DSC and synchrotron small angle X-ray diffraction/scattering as a function of temperature (XRDT) and sodium taurocholate concentration [TC] in the 0–40 mM range ([DPPC]=50 mM) at pH 7.4. The existence of multiple phase transitions (up to 5 peaks within a 5°C interval) in a narrow domain of temperature between 25 and 42°C depending on the [TC]/[lipid] ratio was observed in the DSC curves. XRDT showed that at low ratios they might correspond to transitions between lamellar phases, the structural characteristics of which are given. At higher ratios a lamellar to micellar transition was observed, and the temperature at which it was observed decreased as a function of the TC content. The relationships with DPPC vesicle bilayer permeabilization and solubilization are discussed.     

Copolymerization of ethylene and 1-butene using a Cr—silica catalyst in a slurry reactor

A novel slurry reactor was used to investigate the copolymerization behavior of ethylene and 1-butene in the presence of 1 wt % Cr on Davison silica (Phillips-type) catalyst over the temperature range of 0–50°C, space velocity of about 0.0051 [m³ (STP)]/(g of catalyst) h, and a fixed ethylene to 1-butene feed mole ratio of 95 : 5. The effect of varying the ethylene to 1-butene feed ratios, 100 : 0, 96.5 : 3.5, 95 : 5, 93 : 7, 90 : 10, 80 : 20, and 0 : 100 mol/mol at 50°C was also studied. The addition of 1-butene to ethylene typically increased both copolymerization rates and yields relative to ethylene homopolymerization with the same catalyst, reaching a maximum yield for an ethylene: 1-butene feed ratio of 95 : 5 at 50°C. The incorporation of 1-butene within the copolymer in all cases was less than 5 mol %. The average activation energy for the apparent reaction rate constant, k_a, based on total comonomer mole fraction in the slurry liquid for the ethylene to 1-butene feed mole ratio of 95 : 5 in the temperature range of 50–30°C measured 54.2 kJ/mol. The behavior for temperatures between 30 to 0°C differed with an activation energy of 98.2 kJ/mol; thus, some diffusion limitation likely influences the copolymerization rates at temperatures above 30°C. A kinetics analysis of the experimental data at 50°C for different ethylene to 1-butene feed ratios gave the values of the reactivity ratios, r₁ = 27.3 ± 3.6 and r₂ ≅ 0, for ethylene and 1-butene, respectively. © 1996 John Wiley & Sons, Inc.     

Kinetic study of the 2,2-dimethyl-3-buten-1-yl to 2-methyl-4-penten-2-yl radical rearrangement in the temperature range 37–74°C

The tin hydride method was used to determine the rates of the title rearrangement over the temperature range 37–74°C; the data was combined with the previously reported low temperature kinetic studies to give a new temperature dependent function: at 25°C the calculated rate constant is 5.0 × 10⁶ sec^-1     

Thermal degradation kinetics study and thermal cracking of waste cooking oil for biofuel production

Thermal cracking of waste cooking oil (WCO) for production of liquid fuel has gained special interest due to the growing demand of renewable fuel, depleting fossil fuel reserves and environmental issues. In the present work, thermal cracking of WCO to produce liquid hydrocarbon fuels without any preprocessing has been studied. Moreover, non-isothermal kinetics of WCO using thermogravimetric analysis (TGA) has been studied under an inert atmosphere at various heating rates. According to TGA result, active thermal decomposition of WCO was found to be between 318 and 500 °C. Furthermore, the temperature at which the maximum mass loss rate attained was shifted to higher values as the heating rates increased from 10 to 50 °C min^?1 and the values were found to be approximately similar to that of R ₅₀. Besides, model-free iso-conversion kinetic methods such as Friedman (FM), Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) were used to determine the activation energies of WCO degradation. The average activation energy for the thermal degradation of WCO was found to be 243.7, 211.23 and 222 kJ mol^?1 for FM, KAS and FWO kinetic methods, respectively. Additionally, the cracking of WCO was studied in a semi-batch reactor under an inert atmosphere and the influences of cracking temperature, time and heating rates on product distribution were investigated. From the reaction, an optimum yield of 72 mass% was obtained at a temperature of 475 °C, time of 180 min and a heating rate of 10 °C min^?1. The physicochemical properties studied were in accordance with ASTM standards.     

Poly(p‐phenylene sulfide) nonisothermal cold‐crystallization

The poly(p‐phenylene sulfide) (PPS) nonisothermal cold‐crystallization behavior was investigated in a wide heating rate range. The techniques employed were the usual Differential Scanning Calorimetry (DSC), and the less conventional FT‐IR spectroscopy and Energy Dispersive X‐ray Diffraction (EDXD). The low heating rates (Φ) explored by EDXD (0.1 K min^?1) and FT‐IR (0.5–10 K min^?1) are contiguous and complementary to the DSC ones (5–30 K min^?1). The crystallization temperature changes from 95 °C at Φ = 0.05 K min^?1 to 130 °C at Φ = 30 K min^?1. In such a wide temperature range the Kissinger model failed. The model is based on an Arrhenius temperature dependence of the crystallization rate and is widely employed to evaluate the activation energy of the crystallization process. The experimental results were satisfactorily fit by replacing in the Kissinger model the Arrhenius equation with the Vogel–Fulcher–Tamann function and fixing U* = 6.28 k J mol^?1, the activation energy needed for the chains movements, according to Hoffmann. The temperature at which the polymer chains are motionless (T_∞ = 42 °C) was found by fitting the experimental data. It appears to be reasonable in the light of our previously reported isothermal crystallization results, which indicated T_∞ = 48 °C. Moreover, at the lower heating rate, mostly explored by FT‐IR, a secondary stepwise crystallization process was well evidenced. In first approximation, it contributes to about 17% of the crystallinity reached by the sample. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2725–2736, 2005     

Structure and properties of poly-2,5-distyrylpyrazine

Poly-2,5-distyrylpyrazine (poly-DSP) was investigated by differential thermal analysis (DTA), thermogravimetric analysis (TGA), and measurements of dynamic viscoelastic and electrical properties. From DTA and TGA studies it was confirmed that poly-DSP melts at 321°C and depolymerizes rapidly to the monomer at temperatures between 335°C and 345°C in helium. The polymer is affected by oxygen above 200°C. The E′ value from dynamic viscoelasticity measurements on amorphous film is 2 × 10¹¹ dyne/cm² at room temperature. It decrease abruptly in the temperature range 140–150°C; but the net decrease of E′ within this temperature range is relatively small. The electrical properties of amorphous poly-DSP are characterized by a small temperature dependence of the dielectric constant between room temperature and 100°C. The dielectric loss tangent was observed to be small, and the dc conductivity was extremely small. It is concluded that rotation of the phenyl branches in the polymer occurs above ?30°C and the glass transition occurs at about 150°C. These properties are discussed in some detail in relation to the polymer structure.     

Kinetic mechanism of the thermal decomposition of tobacco

Equations have been derived to describe the chemical kinetic factors that affect the rate of formation of products when a mixture of solid components (tobacco) decomposes on heating. Using these equations, a computer model of tobacco pyrolysis has been constructed which can calculate the gas formation rate/temperature profile from a given set of reaction parameters. By comparing the predictions of the model with experimental results at heating rates between 0.8 and 25 deg C s^?1, a generalised kinetic mechanism for the thermal decomposition of tobacco has been developed. For carbon monoxide and other low molecular weight gases, the mechanism is an independent formation of each gas from one solid tobacco component in each temperature region. Pyrolysis of some individual tobacco components in other studies suggests that each gas is actually produced from many components in each temperature region. This more complex mechanism is kinetically equivalent to the deduced mechanism of independent formation from one component.The region in which a given decomposition reaction takes place moves to higher temperatures as the heating rate increases. The amounts of gases formed over any temperature region from 200 to 900°C can be calculated for a given heating rate using the mechanism and the kinetic constants. The present results imply that 75–90% of the carbon monoxide produced by tobacco decomposition at temperatures up to 900°C during a puff on a cigarette corresponds to that formed in the “low temperature region” (200–450°C) defined for pyrolysis experiments at the lower heating rates of 1–10 deg C s^?1.     

Crystallite growth of rice husk ash silica

The effect of temperature of firing and time of annealing on crystallite size of silica obtained by burning boiled rice husk was studied by the X-ray broadening technique. The results showed that nuclei of disordered cristobalite were present in ash silica, and crystallite growth was governed by two processes, namely nucleation and growth taking place simultaneously with a rate varying with the temperature of treatment. The nucleation process manifested itself in the low temperature range of 800–900°C, while growth was more pronounced in the temperature range 1000–1100°C, occurring with different activation energies of 81.3 and 52.4 cal mole^?1, respectively. Both processes occurred with the same intensity at 964°C. A growth process and crystal perfection followed with an activation energy of 36.8 cal mole^?1.     

Acetone condensation over CaO—SnO<Subscript>2</Subscript> catalyst

Aldol condensation of acetone was studied over solid base CaO—SnO₂ catalyst in the 300—450 °C temperature range and at 15—75 atm pressure in a fixed-bed reactor. The main products are mesityl oxide and isophorone. The high stability of CaO—SnO₂ catalyst performance was observed at pressure of 75 atm giving the acetone conversion of 36—41%. Increase in the temperature and pressure led to a simultaneous raise in acetone conversion. The maximum conversion of 41% was achieved at 400 °C, 75 atm and a flow rate of acetone of 8.1 g h^–1 (g catalyst)^–1.     

Dual entropic and enthalpic processes in the lower critical solution temperature phase separation of poly(vinyl methyl ether) aqueous solutions

In the lower critical solution temperature phase separation of poly(vinyl methyl ether) aqueous solutions, the process corresponding to the weakening of the hydrogen bond interaction with increasing temperature is dominant and occurs over the entire concentration region of solutions and over a broad temperature range from 30 to 41°C, giving rise to the energetic enthalpic effect during phase separation, while the conformational change, that is, collapse of the swollen polymer coils, occurs only in the swelling polymer solution when the water concentration is above 38.3 wt %, giving rise to the entropic effect during phase separation. In addition, the entropic process corresponding to the collapse of the polymer coils occurs in a much narrow theta temperature range from 35.5 to 37°C. If the solution is held at a constant temperature for a sufficiently long time, 90% collapse of the polymer coils occurs in only the 0.5 °C temperature region between 35.5 and 36°C. Accordingly, in the enthalpic process, the most dramatic blueshift of the νC‐O bond peak occurs in the temperature range between 35 and 41°C, while this blueshift is only approximately 2 cm^?1 in the temperature range from 30 to 35°C, prior to the collapse of the polymer coils due to the entropic effect. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 323–330     

Dichte,Leitfähigkeit und Elektrolyse flüssiger Phasen in wasserfreien Systemen vom Typ MCl/AlCl3/SO2 (M = Li,Na)

Density, Conductivity, and Electrolysis of Liquid Phases in Nonaqueous Systems of the Type MCl/AlCl₃/SO₂ (M = Li, Na) The temperature dependence of the density and specific conductivity was determined at liquid phases of the composition MAlCl₄ · nSO₂ + mAlCl₃ (M = Li, n = 3–5.5, m = 0.266; M = Na, n = 1.36–4.56, m = 0.01–0.1). The investigated range was between ?30°C and +45°C. For different compositions it was limited by the liquidus point and by the point, where the SO₂-equilibrium pressure surpassed 1 bar. The densities are between 1.63 and 1.76 g/cm³, the specific conductivities between 0.03 and 0.07 Ω^?1 · cm^?1. In diluted solutions below ?10°C NaAlCl₄ behaves as a strong electrolyte in which dissociation in Na⁺ and AlCl₄^?is prevailing. By electrolysis of the liquid phases at room temperature reversible galvanic cells of the type M/MAlCl₄ · nSO₂/Cl₂, C(M = Li, Na) are generated, which have an open circuit potential between 4.12 and 4.18 volts. The alkali metal deposits are stable in contact with the electrolyte up to 60°C in the case of lithium and 35°C with sodium.     

Degradation studies of some polyesters and polycarbonates—2. Polylactide: Degradation under isothermal conditions,thermal degradation mechanism and photolysis of the polymer

The thermal degradation of polylactide has been studied at several temperatures in the range 230–440°C and the variation of product distribution with temperature has been examined. From experiments at 240–270°C, an energy of activation of 28·5 kcal mol^?1 (119 kJ mol^?1) has been calculated. Mass spectra have been obtained for polylactide and for the cold ring fraction of degradation products in TV A experiments. Both lactide and polylactide have also been heated under closed system conditions and the products have been identified.A mechanism is presented for the thermal degradation, based upon a hydroxyl end-initiated ester interchange process giving cyclic oligomers, lactide, acetaldehyde and carbon monoxide, together with a series of reactions at somewhat higher temperatures dependent upon chain homolysis, giving the same products and also carbon dioxide and methylketene.The photolysis of polylactide at 30°C, using the medium pressure mercury lamp, has been briefly examined.     

Effects of temperature during irradiation and spectrophotometry analysis on the dose response of aqueous dichromate dosimeters

The irradiation temperature dependence of the ⁶⁰Co gamma-ray dose response of a silver-dichromate dosimeter was studied to verify temperature coefficients over 5–60°C, using both low and high range standard-type dosimeters. The temperature coefficients in the temperature range 25–60°C are estimated to be −0.20 and −0.26%/°C respectively at doses 2–10 kGy and 10–50 kGy, although there is a slight tendency of dose dependence. The coefficients covering temperatures of 25–50°C estimated to low and high dose ranges are respectively −0.20 and −0.23%/°C which lead us to confirm the previous data including the ASTM Standards E1401-96, 1997. The effect of temperature during spectrophotometry analysis on molar extinction coefficients was not appreciably observed in the temperature range 5–50°C.     

Aqueous polymerization of methacrylamide

The aqueous polymerization of methacrylamide (I) initiated by KBrO₃–thioglycolic acid (TGA) has been studied at 30 ± 0.2°C in nitrogen. The rate is given by K[M]^1.19 [thioglycolic acid]¹ [KBrO₃]^0.53 for 10–15% conversion. Activation energy was found to be 53.96 kJ/mole (12.92 kcal/mole) in the investigated range of temperature 30–45°C. The role of addition of a series of aliphatic alcohols and some salts was also determined. The kinetics of polymerization was followed iodometrically.     

BaCe0.8Ho0.2O3-a陶瓷的性质与应用

Ceramic BaCe0.8Ho0.2O3-α with orthorhombic perovskite structure was prepared by conventional solid state reaction, and its conductivity and ionic transport number were measured by ac impedance spectroscopy and gas concentration cell methods in the temperature range of 600-1000 ℃ in wet hydrogen and wet air, respectively. Using the ceramics as solid electrolyte and porous platinum as electrodes, the hydrogen-air fuel cell was constructed, and the cell performance at temperature from 600-1000 ℃ was examined. The results indicate that the specimen was a pure protonic conductor with the protonic transport number of 1 at temperature from 600-900 ℃ in wet hydrogen, a mixed conductor of proton and electron with the protonic transport number of 0.99 at 1000 ℃. The electronic conduction could be neglected in this case, thus the total conductivity in wet hydrogen was approximately regarded as protonic conductivity. In wet air, the specimen was a mixed conductor of proton, oxide ion and electron hole. The protonic transport numbers were 0.01-0.09, and the oxide-ionic transport numbers were 0.27-0.32. The oxide ionic conductivity was increased with the increase of temperature, but the protonic conductivity displayed a maximum at 900 ℃, due to the combined increase in mobility and depletion of the carriers. The fuel cell could work stably. At 1000 ℃, the maximum short-circuit current density and power output density were 346 mA/cm^2 and 80 mW/cm^2, respectively.     

Investigation of the complex thermal behavior of fats

The thermal behavior of three ural fats (displaying very different composition), cocoa butter (CB)², lard, and a stearin obtained from anhydrous milk-fat (AMF) fractionation, were studied by both DSC and X-ray diffraction as a function of temperature (XRDT). To perform temperature explorations between –30C and +80C, at rates identical to those used for DSC and ranging from 0.1 K min^–1 to 10 K min^–1, a new set of X-ray sample-holders, temperature-controlled by Peltier effect, has been developed. It is shown that the three more stable polymorphic forms of CB were easily characterized by either X-ray diffraction or DSC, and existence of two -3L forms was confirmed. On the contrary, the more complex polymorphism of lard and AMF required combined examination by DSC and XRDT and the brightness of the synchrotron source for studies at the highest heating rates. Quantitative analysis of the long spacings of XRDT recordings is invaluable for interpretation of thermal events. For instance, it was found that the simultaneous formation of two polymorphic forms, of apparent long spacing of 34 and 42 å, at the onset of lard crystallization might explain the difficulty of its fractionation.Special thanks to Courtney P. Mudd (NIH, Bethesda) for his pertinent advice on the mounting and use of thermoelectric devices. The study of lard crystallization was initiated by Valerie Portalier and suggested by Jean-Luc Vendeuvre of CTSCCV (Maisons-Alfort). For the AMF part of this study, stearin was fractionated by ADRIA Normandie, while characterization of its thermal properties was performed as part of a research program funded by ARILAIT Recherches and the French Ministry of Research and Technology.     

Trapping of hydride forming elements within miniature electrothermal devices. Part 3. Investigation of collection of antimony and bismuth on a molybdenum foil strip following hydride generation

The interaction of stibine and bismuthine with a surface of bare and modified (Pt, Ir and Rh) molybdenum foil strips was investigated by atomic absorption spectrometry with a miniature hydrogen flame atomizer. Different trapping behavior of both analytes was observed contrary to selenium and arsenic hydrides. Maximum trapping efficiency of Sb and Bi is achieved at lower temperatures of 650–750 °C and 500–600 °C, respectively. Absence of hydrogen in argon does not affect trapping of these elements, whereas trapping of As and Se is feasible only in the presence of hydrogen. All used modifiers inhibit trapping of Bi and Sb when their amount exceeds 30 μg. Collected Sb is completely released at temperatures above 2200 °C, whereas a temperature of 1 200 °C is sufficient for vaporization of Bi. Aerodynamic conditions of the injected gas near the molybdenum surface play the same role in trapping both analytes as for As and Se. Maximum trapping efficiencies are achieved at total gas flow rates of 60–70 ml min^− 1 and with a capillary distance of 2 mm. Trapping of Sb is not influenced within the whole interferent mass range of 0–30 μg of As and Se, and 0–300 ng of Bi. Trapping of other analytes is affected by 1 to 2 orders of magnitude higher amounts of concomitant hydrides. According to thermodynamic calculations, the competitive occupation of active sites on the molybdenum surface by the AsO (g) and SbO (g) species and the formation of the inactive analyte–interferent diatomic BiSe (g) and AsSe (g) species can probably be the reason for these interference effects.     

Effect of Polycondensation Reaction Conditions on the Properties of Thermotropic Liquid‐Crystalline Copolyester

In this study a range of wholly aromatic copolyesters based on kink m‐acetoxybenzoic acid (m‐ABA) monomer (33 mol%) and equimolar‐linear p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA) and terephthalic acid (TPA) monomers (67 mol%) have been synthesized by melt polycondensation reaction process at 280°C and 260°C for different time intervals. Characterization of copolyesters were performed by solution viscosity measurement, wide–angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), hot‐stage polarized light microscopy, proton‐nuclear magnetic resonance analysis (¹H‐NMR). According to the results obtained, copolyesters showed thermotropic liquid crystalline behavior in an appropriate temperature range. The copolyesters were prepared in high yields. It was observed that the intrinsic viscosities of the copolyesters are increased regularly with increasing polymerization time and temperature. All the copolyesters were soluble in a trifluoroacetic acid/dichloromethane (30:70 v/v) except the copolyesters which were synthesized at 280°C in 5 h. According to the WAXD results; the degree of crystallinity of copolyesters were found to be between 5–15%. DSC and hot stage polarized light microscopy results showed that all the copolyesters are melt processable and a significant molecular interaction exist in a very broad temperature range (160°C and 165°C) in the nematic mesophase. The T_g values are increased with an increasing polycondensation reaction time and temperature and they were observed between 93–126°C. Fibers prepared by a hand‐spinning technique from the polymer melt exhibit well‐developed fibrillar structure parallel to the fiber axis.     

13C, 1H and 31P dynamic NMR studies of tetraalkyldiphosphanes: Barrier to internal rotation about the P?P Bond in tetraisopropyldiphosphane

The ¹H, ³¹P and ¹³C NMR spectra of tetramethyldiphosphane (1), tetraethyldiphosphane (2) and tetraisopropyldiphosphane (3) have been studied in the temperature range 30 to ?150°C and at magnetic induction up to 5.87 T. In the range ?100 to ?135 °C, the ¹H and ¹³C spectra of 3 show important changes which can be attributed to freezing the interconversion between two equivalent non-trans conformations. The line shape analysis of the ¹³C signals leads to ΔG^≠ = 29.4 kJ mol^?1 at ?113 °C for the dynamic process involved. The spin coupling parameters ¹J(PP) and N(PC) = ¹J(PC) + ²J(PC) observed for 1 in the temperature range 30 to ?120 °C show variations which could be due to a preference for the trans conformation in this diphosphane.     

A Measurement Technique for Organic Nitrates and Halocarbons in Ambient Air

A cryogenic preconcentration/high-resolution gas chromatographic technique has been developed for the rapid, simultaneous quantitation of C₁–C₄ organic nitrates and halocarbons in ambient air. Whole-air samples are collected in Tedlar^TM bags by an evacuated-chamber method. Samples were stable in 0.010-cm-thick bags for 24 h if they were immediately stored in a freezer at −25°C. Analytes in a 50-cm³ air sample were efficiently preconcentrated on fused-silica beads at −180°C and thermally desorbed at 30°C. High-resolution gas chromatography with a cross-linked polydimethylsiloxane fused-silica capillary column and an electron-capture detector were used for separation and quantitation of the analytes. An analysis time of about 12 min was facilitated by sample cryofocusing at −180°C and oven temperature programming. Recoveries of the analytes by the evacuated-chamber method were better than 95%. The sensitivity of the technique for sample volumes of 50 cm³ is in the sub-parts-per-trillion by volume (ppt[v]) range for many of the analytes, with an average precision of about ±5% for analytes at levels of about 10 ppt(v).