Small angle neutron scattering study of two nonionic surfactants in water micellar solutions

Two classic nonionic surfactants — C₁₄E₇ (heptaethylene glycol monotetradecyl ether) and C₁₀E₇ (heptaethylene glycol monodecyl ether) were investigated in heavy water solution for concentration c = 0.17% (dilute regime) at different temperatures in the range t = 10–35°C by small angle neutron scattering (SANS) method. In the case of C₁₄E₇ surfactant — for all temperatures at c = 0.17% there are two axial ellipsoidal micelles with longer axis 15 nm at 10°C and 49.5 nm at 35°C in investigated solutions. For C₁₀E₇ surfactant at the same concentration of solution and temperature — two axial ellipsoidal micelles were observed, too. The longer axis is equal to 7.5 nm at 10°C, 9 nm at 20°C and at 35°C this axis is equal to 12 nm. Micelles of C₁₀E₇ nonionic surfactant are smaller than those of C₁₄E₇ surfactant in the same experimental conditions.      

An isothermal titration calorimetry study of the interactions between an oxyphenylethylene/oxyethylene diblock copolymer and sodium dodecyl sulfate

Interactions between the diblock copolymer S₁₅E₆₃ and the surfactant sodium dodecyl sulfate (SDS) have been investigated by isothermal titration calorimetry (ITC) in the temperature range 10–40°C. At 20°C, the block copolymer is associated into micelles with a hydrodynamic radius of 11.6?nm, which is composed of a hydrophobic styrene oxide (S) core and a water-swollen oxypolyethylene (PEO) corona. The copolymer/surfactant system has been studied at a constant copolymer concentration of 0.25?wt% and over a wide range of surfactant concentration, from 7.5?×?10^?6 up to 0.3?M. The titration calorimetric data for SDS in the temperature range 10–20°C presents a first endothermic increase indicating the formation of mixed copolymer rich-surfactant micelles. From that point, important differences in the ITC plots for surfactant titrations in the presence and in the absence of the copolymer are present. A shallow second endothermic peak is assigned to the interaction between SDS molecules and copolymer molecules resulting from the beginning of micelle disruption. An exothermic peak indicates the end of this disruption where only SDS micelles attached to single copolymer monomers are present, as shown by DLS in a previous paper. At higher temperatures in the range 25–40°C, the first endothermic maximum is not totally shown because interactions between surfactant and block copolymer start at very low SDS concentrations. Moreover, the second endothermic peak is absent and the exothermic minimum is less pronounced as a consequence of the increased micellization of the block copolymer.     

Small-angle neutron scattering studies of nonionic surfactant: Effect of sugars

Micellar solution of nonionic surfactantn-dodecyloligo ethyleneoxide surfactant, decaoxyethylene monododecyl ether [CH₃(CH₂)₁₁(OCH₂CH₂)₁₀OH], C₁₂E₁₀ in D₂O solution have been analysed by small-angle neutron scattering (SANS) at different temperatures (30, 45 and 60° C) both in the presence and absence of sugars. The structural parameters like micelle shape and size, aggregation number and micellar density have been determined. It is found that the micellar structure significantly depends on the temperature and concentration of sugars. The micelles are found to be prolate ellipsoids at 30° C and the axial ratio of the micelle increases with the increase in temperature. The presence of lower concentration of sugar reduces the size of micelles and it grows at higher concentration of sugar. The structure of micelles is almost independent of the different types of sugars used.     

Viscoelastic properties of tri(O.tolyl) phosphate from light scattering and ultrasonic techniques

From our light scattering and the literature ultrasonic experiments, the shear and longitudinal moduli of the tri(O-tolyl)phosphate are calculated in a temperature range of nearly 70°C above Tg. From ?2°C to + 10°C the retardational compliance J_R/J∞ is found to be equal to 8.0 ± 0.1 and the retardational time C_R calculated. The relaxational modulus is obtained from ?55 to +10°C.     

Synthesis and electric properties of perovskite Pr0.6Ca0.4Fe0.8Co0.2O3 for SOFC applications

In this study, polycrystalline powder Pr_0.6Ca_0.4Fe_0.8Co_0.2O₃ (PCFC) was synthesized by a sol–gel process. This oxide was analyzed by X-ray powder diffraction. Synthesized Pr_0.6Ca_0.4Fe_0.8Co_0.2O₃ showed up to be single phase and belongs to the orthorhombic crystalline system with a Pbnm space group. The microstructural features of the synthesized products display particles having an irregular morphology and a size in the range of 50–100 nm. X-ray diffraction (XRD) analysis shows the chemical compatibility between the PCFC cathode and the electrolyte Sm-doped ceria since no reaction products were honored when the material was mixed and co-fired at 1,000 °C for 168 h. The thermal expansion coefficient of PCFC 16.9?×?10^?6 °C^?1 is slightly higher than that of Ce_0.8Sm_0.2O_1.9 (SDC) over the studied temperature range. The greater contribution to the total resistance of the electrode is the electrochemical resistance associated with oxygen exchange in the cathode surface (0.96 Ωcm²). The dc four-probe measurement indicated that PCFC exhibits fairly high electrical conductivity, over 100 S cm^?1 at T?≥?500 °C, making this material promising as a cathode material for intermediate temperature solid oxide fuel cells.     

Microphase separation in weakly charged hydrophobic polyelectrolytes

Aqueous solutions of a well-defined poly(N-isopropylacrylamide-co-sodium 2-acrylamido-methylpropanesulfonate) (NIPAM/NaAMPS in a 95/5 molar ratio) have been investigated by means of small-angle neutron scattering (SANS) and rheological experiments as a function of temperature ( 25^° C T 60^° C) and polymer concentration ( 0.5wt% C 12wt%). The solutions remain optically transparent and isotropic over the whole temperature range, in contrast with the homopolyNIPAM which precipitates above its lower critical solution temperature (LCST = 32^° C). Upon addition of salt, the systems undergo a micro-macrophase separation. At temperatures above 45^° C, the SANS spectra exhibit a sharp peak at a scattering wave vector, q _max, which increases slightly with temperature. At high temperature ( T∼ 60^° C), the scattered intensity follows a power law I(q) ∼q ^-4 in the asymptotic regime, characteristic of two-density media with sharp interfaces, and q _max is found to vary with polymer concentration as q _max∼C ^0.22. Estimates of the typical sizes give values between 40 ? and 200 ?. These results provide a strong evidence of a thermally induced microphase separation, which is corroborated by the very sharp increases of the viscosity (over 2 decades) and of the stress relaxation time of the solutions, occurring in the temperature range where the scattering peak is observed. The results are discussed and compared with the theoretical models proposed for weakly charged polyelectrolytes in a poor solvent. Received 1 October 2001     

Na+ ion conductivity and crystallographic cell characterization in the Hf-nasicon system Na1+xHf2SixP3−xO12

We have measured the effect of varying the mobile ion concentration on the sodium ion conductivity in the Hf-Nasicon system, Na_1+xHf₂Si_xP_3-xO₁₂, for 1.4 ? x ? 2.8. The conductivity is greatest for Na_3.2Hf₂Si_2.2 P_0.8O₁₂: σ_25°C = 2.3 × 10^?3 (ω cm)^?1, and σ_250°C = 1.7 × 10^?1 (ω cm)^?1. These values are approximately 50% greater and worse, respectively, than the values reported for the best Zr-Nasicon. We have characterized the variation of lattice parameters with composition and found the behavior to be similar to that of Zr-Nasicon. A small distortion from rhombohedral to monoclinic symmetry occurs for compositions 1.8 ? x ? 2.2.     

The chemical stability and conductivity improvement of protonic conductor BaCe0.8 − x Zr x Y0.2O3 − δ

A series of BaCe_0.8???x Zr _x Y_0.2O_3???δ (BCZYx) (x?=?0, 0.2, 0.4, 0.6, 0.8) powders were prepared by EDTA–citrate complexing sol–gel process in this paper. The electrical conducting behavior, as well as chemical stability, was investigated. X-ray diffraction (XRD) results reveal that all samples are homogenous perovskite phases. Observed from XRD patterns and thermogravimetric curves, the samples with x?≥?0.4 survive in the pure CO₂, while samples with various Zr contents all present structurally stable against steam at 800 °C. The Zr-free sample of BaCe_0.8Y_0.2O_3???δ possesses the maximum bulk conductivity, 4.25?×?10^?2 S/cm, but decomposes into Ba(OH)₂ and Ce_0.8Y_0.2O_3???δ in steam. A negative influence of increasing Zr content on the conductivity of BCZYx can be observed by impedance tests. Considering the effect of temperature on the bulk conductivity, BCZY0.4 is preferred to be applied in SOFC as a protonic conductor, ranging from 1.52?×?10^?4 to 1.51?×?10^?3 S/cm (500–850 °C) with E _a?=?0.859 eV, which is proved to be a good protonic conductor with t _H+?≥?0.9.     

Study of structural and electrical properties of thin NiO<Subscript>x</Subscript> films prepared by ion beam sputtering of Ni and subsequent thermo-oxidation

Nickel oxide thin films were prepared by thermal annealing of thin Ni films (thickness ca 47?nm) deposited by ion beam sputtering. The thermal annealing was performed at 350 °C and 400 °C with elected time (1–7 hours) in a quartz furnace opened to air. During annealing the samples underwent structural changes, as well as changes of their electrical properties. The structural properties (surface morphology and occurrence of crystalline phases) were analyzed by the AFM and XRD methods, O and Ni depth concentration profiles by the NRA method, and electrical properties (sheet resistance) by the van der Pauw 4-point technique. The sheet resistance (R _S ) of the as-deposited sample was found to be 12.03 Ω/□; after open air thermal annealing at 350 °C for 1 h the value was found to be almost the same, 11.67 Ω/□. After 2 h of annealing, however, a sharp increase in the sheet resistance (R _S = 1.46 MΩ/□) was observed. At this stage the deposit formed largely oxidized Ni layer with a distinct polycrystalline structure. The sharp increase of sheet resistance was ascribed to the oxidation of the Ni layer, leaving only a smaller amount of isolated Ni particles unoxidized. Almost complete oxidation was found after 7 h of annealing at 350 °C. At 400 °C was almost complete oxidation recorded already after 1 h of annealing.     

Distribution of light alkanes in the reaction of graphite hydrogenation at pressure of 0.1–7.8 GPa and temperatures of 1000–1350°C

ABSTRACT

We studied the effect of pressure and temperature on the hydrocarbon (HC) chain length distribution and total amount of HCs in the reaction of direct graphite hydrogenation at pressures of 0.1–7.8?GPa and temperatures of 1000–1350°C. An increase in pressure was found to lead both to an increase in the absolute yield of HCs due to direct graphite hydrogenation and to chain elongation of HC products. Light alkanes predominate among HCs in the entire studied range of P–T parameters. However, their concentration in quenched fluids increases as pressure is elevated, from less than 10?rel.% at 0.1?GPa to more than 40–50?rel.% at P?≥?3.8?GPa. Methane is actually the only light alkane among reaction products at 0.1?GPa and 1000°C, while it is a minor component at 7.8?GPa and 1350°C. The most stable alkane at pressures above 3.8?GPa is ethane (C₂H₆).     

Experimental investigation of flame spreading over pure methane hydrate in a laminar boundary layer

Flame spreading over pure methane hydrate in a laminar boundary layer is investigated experimentally. The free stream velocity (U_∞) was set constant at 0.4 m/s and the surface temperature of the hydrate at the ignition (T_s) was varied between ?10 and ?80 °C. Hydrate particle sizes were smaller than 0.5 mm. Two types of flame spreading were observed; “low speed flame spreading” and “high speed flame spreading”. The low speed flame spreading was observed at low temperature conditions (T_s = ?80 to ?60 °C) and temperatures in which anomalous self-preservation took place (T_s = ?30 to ?10 °C). In this case, the heat transfer from the leading flame edge to the hydrate surface plays a key role for flame spreading. The high speed flame spreading was observed when T_s = ?50 and ?40 °C. At these temperatures, the dissociation of hydrate took place and the methane gas was released from the hydrate to form a thin mixed layer of methane and air with a high concentration gradient over the hydrate. The leading flame edge spread in this premixed gas at a spread speed much higher than laminar burning velocity, mainly due to the effect of burnt gas expansion.     

Structural investigations of Ge nanoparticles embedded in an amorphous SiO2 matrix

Transmission electron microscopy and X-ray photoelectron spectroscopy analyses are performed to investigate Ge nanoparticles embedded in an amorphous SiO₂ matrix. GeSiO thin films are prepared by two methods, sol?Cgel and radio frequency magnetron sputtering. After the deposition, the sol?Cgel films are annealed in either N₂ (at 1 atm and 800 °C) or H₂ (at 2 atm and 500 °C), and the sputtered films in H₂ (at 2 atm and 500 °C), to allow Ge segregation. Amorphous Ge-rich nanoparticles (3?C7 nm size) are observed in sol?Cgel films. Crystalline Ge nanoparticles in the high pressure tetragonal phase (10?C50 nm size) are identified in the sputtered films. The size of the nanoparticles increases with Ge concentration in the volume of the film. At the film surface, the Ge concentration is much larger that in the volume for both sol?Cgel and sputtered films. At the same time, at the film surface, only oxidized Ge is observed.     

PVA-assisted synthesis and characterization of nano-crystalline La3+ and Mg2+ co-doped CeO2 electrolyte for intermediate-temperature solid oxide fuel cells

A series of nano-crystalline ceria-based solid solution electrolyte, Ce_0.8La_0.2?x Mg_xO_2?δ (x?=?0.0, 0.05, 0.10, 0.15, and 0.2), were synthesized via the polyvinyl alcohol (PVA) assisted combustion method, and then characterized to the crystalline structure, powder morphology, sintering micro-structure, and electrical properties. Present study showed that Ce_0.8La_0.2?x Mg _x O_2?δ was exceedingly stable as a cubic phase in all temperature range and exhibited fine crystals ranging from 15 to 20 nm. After sintering at 1,400 °C, the as-prepared pellets exhibited a dense micro-structure with 96 % of theoretical density. The electrical conductivity was studied using AC impedance spectroscopy and it was observed that the composition Ce_0.8La_0.1?Mg_0.1O_2?δ showed higher electrical conductivity of 0.020 S?cm^?1 at 700 °C. The thermal expansion was measured using dilatometer technique in the temperature range 30–1,000 °C. The average thermal expansion coefficient of Ce_0.8La_0.1?Mg_0.1O_2?δ was 12.37?×?10^?6 K^?1, which was higher than that of the commonly used SOFC electrolyte YSZ (~10.8?×?10^?6 K^?1).     

Recrystallization of hexagonal silicon carbide after gold ion irradiation and thermal annealing

Silicon carbide (SiC) single crystals with the 6H polytype structure were irradiated with 4.0-MeV Au ions at room temperature (RT) for increasing fluences ranging from 1?×?10¹² to 2?×?10¹⁵ cm^?2, corresponding to irradiation doses from ~0.03 to 5.3 displacements per atom (dpa). The damage build-up was studied by micro-Raman spectroscopy that shows a progressive amorphization by the decrease and broadening of 6H-SiC lattice phonon peaks and the related growth of bands assigned to Si–Si and C–C homonuclear bonds. A saturation of the lattice damage fraction deduced from Raman spectra is found for ~0.8?dpa (i.e. ion fluence of 3?×?10¹⁴ cm^?2). This process is accompanied by an increase and saturation of the out-of-plane expansion (also for ~0.8?dpa), deduced from the step height at the sample surface, as measured by phase-shift interferometry. Isochronal thermal annealing experiments were then performed on partially amorphous (from 30 to 90%) and fully amorphous samples for temperatures from 200 °C up to 1500 °C under vacuum. Damage recovery and densification take place at the same annealing stage with an onset temperature of ~200 °C. Almost complete 6H polytype regrowth is found for partially amorphous samples (for doses lower than 0.8 dpa) at 1000 °C, whereas a residual damage and swelling remain for larger doses. In the latter case, these unrelaxed internal stresses give rise to an exfoliation process for higher annealing temperatures.     

Local atomic and magnetic structures of nanocrystalline Fe75Cr10B15 alloy

The crystal, local atomic and magnetic structures of Fe₇₅Cr₁₀B₁₅ alloys annealed at 440?C473°C for 5 min have been studied using X-ray diffraction and ⁵⁷Fe M?ssbauer spectroscopy. At the annealing temperature T _a = 440°C, nanocrystals of the ??-Fe phase (??1%) precipitate in the amorphous matrix of the alloy. The complete crystallization of the amorphous alloy occurs at T _a = 473°C with the formation of ??-Fe nanocrystals 26 ± 2 nm in size and nanocrystals of tetragonal boride t-Fe₃B 47 ± 2 nm in size. It has been found that chromium atoms are located in nanocrystals of the ??-Fe and y-Fe₃B types. The distribution functions of hyperfine fields in the nanocrystalline Fe₇₅Cr₁₀B₁₅ alloy reconstructed from the M?ssbauer spectra (at T _a = 473°C) show that there are three allowed states of iron atoms in the ??-Fe phase and three equally probable crystallographic nonequivalent states of iron in the t-(Fe,Cr)₃B phase. The chromium concentration x in the ??-Fe(Cr) phase is found to be ??10 at %. The substitution of chromium atoms for iron atoms in t-Fe₃B substantially decreases local magnetic moments of the iron atoms.     

Physico-chemical properties of micellar sodium taurodeoxycholate solutions. Ultrasonic behaviour and viscosity

Summary Ultrasonic absorption and velocity have been measured in sodium taurodeoxycholate solutions, at concentrations ranging between 0.1 and 0.4 mol kg⁻¹ and at temperatures of 25, 35 and 45°C. In addition, viscosity measurements have been performed. The ultrasonic results show that at least two kinetic processes occur in such systems. At high frequency the kinetic processes may be related to monomer-micelle exchange, while at lower frequency they may be related to the change of size and shape of the solute aggregates. The trend of the activation energy of the viscous flow confirms the increase of the aggregation number of the micelles at higher molality. Paper presented at the “Meeting on Lyotropics and Related Fields”, held in Rende, Cosenza, September 13–18, 1982.     

Influence of Nitrogen Supply and Temperature on Stable Carbon Isotope Ratios in Plants of Different Photosynthetic Pathways (C3, C4, CAM)

Abstract

One representative species of each of the three photosynthetic pathways (C₃, C₄, CAM) were cultivated in growth chambers with high and low nitrogen nutrition level respectively once at 20°C day/13°C night temperature, once at 30°C day/13°C night. Leaf conductances and δ¹³C values of the leaves of each plant were determined. At 20°C day temperature the C₃ species showed higher leaf conductance with low nitrogen nutrition level than with high nitrogen level, which is also reflected in a more negative δ¹³C value, whereas both C₄ and CAM plants did not respond in this manner to nitrogen supply. An increase of day temperature to 30°C diminished the significant response of the C₃ plant, while the response of C₄ and CAM representatives to nitrogen nutrition did not change markedly.     

Determination of the he pressure in bubbles formed during α-implantation of Ni

Abstract

At T?90°C, Ni single crystals were uniformly implanted to a depth of 10 μm with multi-energy He ions (E≤5.2 MeV), to concentrations from 0.06 to 1.1 at.%. From a small-angle X-ray scattering study, helium was found to be trapped in small bubbles with radii of 5.6 to 12 Å. The average distance between bubbles of about 80 Å was found to be independent of the implantation dose. At the higher concentration, CH_c 1.1%, the bubbles were found to be strongly over-pressurized, i.e. the He pressure in the larger bubbles was determined to be as high as 300 kbar with a He atom/vacancy ratio of 2.     

Mechanism of the formation of a diamond nanocomposite during transformations of C60 fullerite at high pressure

The results of an investigation of the transformation of C₆₀ fullerite to diamond under pressure through intermediate three-dimensionally polymerized and amorphous phases are reported. It is found that treatment of fullerite C₆₀ at pressures 12–14 GPa and temperatures ∼1400°C produces a nanocrystalline graphite-diamond composite with a concentration of the diamond component exceeding 50%. At lower temperatures (700–1200°C) nanocomposites consisting of diamondlike (sp ³) and graphitic (sp ²) amorphous phases are formed. The nanocomposites obtained have extremely high mechanical characteristics: hardness comparable to that of best diamond single crystals and fracture resistance two times greater than that of diamond. Mechanisms leading to the transformation of C₆₀ fullerite into diamond-based nanocomposites and the reasons for the high mechanical characteristics of these nanocomposites are discussed. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 11, 822–827 (10 June 1999)     

High-temperature cation ordering in olivine: an in situ Mössbauer study of synthetic (Mg0.55Fe0.45)2 SiO4

High-temperature in situ Mössbauer spectroscopy measurements (300–950°C) were done on synthetic olivine of composition (Mg_0.55Fe_0.45)₂ SiO₄ (=Fa45) in order to study the distribution of Fe^2?+? over the M1 and M2 octahedral sites. The spectra are fit with two doublets, which are assigned to Fe^2?+? at the M1 (smaller splitting) and M2 sites. The Fe^2?+? site-occupancies at M1 and M2, obtained from the Mössbauer relative areas, suggest that Fe^2?+? has a slight preference for the M1 site at temperatures below ~500°C, with a tendency of disordering around this temperature. At higher temperatures, Fe^2?+? again prefers to occupy the M1 site, where it shows a considerable order at this site up to 750°C. At still higher temperatures, the spectra indicated partial reduction of the Fa-component into metallic iron and the resolution of the doublets was severely deteriorated.