Effect of europium(III) chloride on the aggregation behavior of sodium dodecyl sulfate

The effect of EuCl3 on the aggregation processes of sodium dodecyl sulfate was investigated. Electrical conductivity data, combined with Eu(III) luminescence measurements, suggest that the formation of micelles involving EuCl3 and SDS occurs at low SDS concentration; the formation of these mixed aggregates was also monitored by light scattering, which indicates that the addition of EuCl3 to SDS concentration at values below the critical micelle concentration of the pure surfactant results in a much higher light scattering than that found just with SDS micelles. It was also found that the Eu(III)/DS- complexes are formed with a binding ratio which varies between 20 and 4, depending on the initial concentration of Eu(III). As the concentration increases, turbidity occurs initially, but solutions become clear subsequently. In contrast to the behavior of SDS in the presence of aluminum(III), no flocculation was observed. From the analysis of electrical conductivity data and comparison with other systems, it is suggested that growth of aggregates happens, probably with formation of nonspherical systems. At the highest concentrations these may involve just Eu(III) and DS- ions. The effect of temperature on the SDS micellization process was studied. The calculated free energy of SDS micellization is not dependent on the initial EuCl3 but is dependent on the final balance between the presence of counterions in solution (ionic strength) and the temperature.     

Unconventional, highly selective CO2 adsorption in zeolite SSZ-13

Low-pressure adsorption of carbon dioxide and nitrogen was studied in both acidic and copper-exchanged forms of SSZ-13, a zeolite containing an 8-ring window. Under ideal conditions for industrial separations of CO(2) from N(2), the ideal adsorbed solution theory selectivity is >70 in each compound. For low gas coverage, the isosteric heat of adsorption for CO(2) was found to be 33.1 and 34.0 kJ/mol for Cu- and H-SSZ-13, respectively. From in situ neutron powder diffraction measurements, we ascribe the CO(2) over N(2) selectivity to differences in binding sites for the two gases, where the primary CO(2) binding site is located in the center of the 8-membered-ring pore window. This CO(2) binding mode, which has important implications for use of zeolites in separations, has not been observed before and is rationalized and discussed relative to the high selectivity for CO(2) over N(2) in SSZ-13 and other zeolites containing 8-ring windows.     

Evolution of the 251 cm-1 infrared phonon mode with temperature in Ba0.6K0.4Fe2As2

The far-infrared optical reflectivity of an optimally doped Ba1-xKxFe2As2(x =0.4) single crystal is measured from room temperature down to 4 K. We study the temperature dependence of the in-plane infrared-active phonon at 251 cm-1 . This phonon exhibits a symmetric line shape in the optical conductivity, suggesting that the coupling between the phonon and the electronic background is weak. Upon cooling down, the frequency of this phonon continuously increases, following the conventional temperature dependence expected in the absence of a structural or magnetic transition. The intensity of this phonon is temperature independent within the measurement accuracy. These observations indicate that the structural and magnetic phase transition might be completely suppressed by chemical doping in the optimally doped Ba0.6K0.4Fe2As2 compound.     

Fluorene: An extended experimental thermodynamic study

This work reports new experimental thermodynamic results on fluorene. Vapor pressures of both crystalline and liquid phases were measured using a pressure gauge (capacitance diaphragm manometer) and Knudsen effusion methods over a wide temperature range (292.20 to 412.16) K yielding accurate determination of enthalpy and entropy of sublimation and of vaporization. The enthalpy of sublimation was also determined using Calvet microcalorimetry. The enthalpy of fusion was derived from vapor pressure results and from d.s.c. experiments. Static bomb calorimetry was used to determine the enthalpy of combustion of fluorene from which the standard enthalpy of formation in the crystalline phase was calculated. The enthalpy of formation in the gaseous phase was calculated combining the result derived for the crystalline phase with the enthalpy of sublimation.     

Evolution of the 251 cm-1 temperature in infrared phonon mode with Ba0.6K0.4Fe2As2

The far-infrared optical reflectivity of an optimaUy doped Ba1-xKxFe2As2 （x = 0.4） single crystal is measured from room temperature down to 4 K. We study the temperature dependence of the in-plane infrared-active phonon at 251 em-1. This phonon exhibits a symmetric line shape in the optical conductivity, suggesting that the coupling between the phonon and the electronic background is weak. Upon cooling down, the frequency of this phonon continu- ously increases, following the conventional temperature dependence expected in the absence of a structural or magnetic transition. The intensity of this phonon is temperature independent within the measurement accuracy. These observa- tions indicate that the structural and magnetic phase transition might be completely suppressed by chemical doping in the optimally doped Bao.6Ko.4Fe2As2 compound.     

Additive-free Aqueous Dispersions of Two-Dimensional Materials with Glial Cell Compatibility and Enzymatic Degradability

Water-dispersible two-dimensional (2D) materials are desirable for diverse applications. Aqueous dispersions make processing safer and greener and enable evaluation of these materials on biological and environmental fronts. To evaluate the effects of 2D materials with biological systems, obtaining dispersions without additives is critical and has been a challenge. Herein, a method was developed for obtaining additive-free aqueous dispersions of 2D materials like transition metal dichalcogenides and hexagonal boron nitride (h-BN). The nanosheet dispersions were investigated through spectroscopic and microscopic methods, along with the role of size on stability. The aqueous media enabled investigations on cytocompatibility and enzymatic degradation of molybdenum disulphide (MoS₂) and h-BN. Cytocompatibility with mixed glial cells was observed up to concentrations of 100 μg mL⁻¹, suggesting their plausible usage in bioelectronics. Besides, biodegradation using human myeloperoxidase (hMPO) mediated catalysis was investigated through Raman spectroscopy and electron microscopy. The findings suggested that additive-free 2H-MoS₂ and h-BN were degradable by hMPO, with 2H-phase exhibiting better resistance to degradation than the 1T-phase, while h-BN exhibited slower degradation. The findings pave a path for incorporating 2D materials in the burgeoning field of transient bioelectronics.     

Asymptotically sharp uniform estimates in a scalar spectral stiff problemEstimations asymptotiques uniformes pour le spectre d'un problème scalaire raide

Estimates of convergence rates for rescaled eigenvalues of the stiff Neumann problem for the Laplacian are obtained. The bounds are expressed in terms of the stiffness ratio and properties of the limit spectrum both for low and middle frequency ranges. To cite this article: M. Lobo et al., C. R. Mecanique 331 (2003).     

Excess Gibbs energy for six binary solid solutions of molecularly simple substances

In this paper we apply the method developed in a previous study of Ar + CH₄ to the evaluation of the excess Gibbs energy G^{E S} for solid solutions of two molecularly simple components The method depends on combining information on the excess Gibbs energy G^{E L} for the liquid mixture of the two components with a knowledge of the (T, x) solid-liquid phase diagram Certain thermal properties of the pure substances are also needed G^{E S} has been calculated for binary mixtures of Ar + Kr, Kr + CH₄, CO + N₂, Kr + Xe, Ar + N₂ and Ar + CO. In general, but not always, the solid mixtures are more non-ideal than the liquid mixtures of the same composition at the same temperature Except for the Kr + CH₄ system, the ratio $\text{r =}\text{G}{}^{\mathrm{E\; S}}\text{G}{}^{\mathrm{E\; L}}$ is larger the richer the solution in the component with the smaller molecules     

Effects of pH on the morphology of iron oxides synthesized under gamma-irradiation

Summary 190, Kinshasa XI, Kinshasa, République Démocratique du C