Results 1 - 10 of 38850
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[en] Highlights: ► Mutual diffusion coefficients of paracetamol in aqueous dilute solutions. ► Influence of the thermodynamic factors on the variation of their mutual diffusion coefficients. ► Estimation of the mutual limiting diffusion coefficients of the molecular, Dm0, and ionized forms, D±0, of this drug. - Abstract: Binary mutual diffusion coefficients measured by the Taylor dispersion method, for aqueous solutions of paracetamol (PA) at concentrations from (0.001 to 0.050) mol·dm−3 at T = 298.15 K, are reported. From the Nernst–Hartley equation and our experimental results, the limiting diffusion coefficient of this drug and its thermodynamic factors are estimated, thereby contributing in this way to a better understanding of the structure of such systems and of their thermodynamic behaviour in aqueous solution at different concentrations.
[en] From extraction experiments and ?-activity measurements, the exchange extraction constants corresponding to the general equilibrium M2+ (aq) + Sr2+ (org) ↔ M2+ (org) + Sr2+ (aq) taking place in the two-phase water-phenyltrifluoromethyl sulfone (abbrev. FS 13) system (M2+ Mg2+, Ca2+, Ba2+, Cu2+, Zn2+, Cd2+, Pb2+, UO22+, Mn2+, Fe2+, Co2+, Ni2+; aq = aqueous phase, org = FS 13 phase) were evaluated. Furthermore, the individual extraction constants of the M2+ cations in this two-phase system were calculated; they were found to increase in the series of Mg2+, UO22+ < Ca2+, Co2+ < Cd2+, Ni2+ < Zn2+ < Cu2+, Mn2+, Fe2+ < Pb2+ < Ba2+. (author)
[en] In the present work, impingement behaviour of an aqueous urea solution is investigated experimentally. The effects of droplet diameter, impact velocity and substrate temperature are evaluated by monitoring single droplet impingement with a high-speed camera. Results allow the formulation of four different interaction regimes and a regime map depending on hydrodynamic and thermal parameters is proposed. The regimes deposition, splash, boiling-induced breakup, rebound with breakup and the transition boundaries are discussed in detail. Results show that the solute significantly affects the outcome of droplet impingement promoting droplet disintegration by enhanced nucleation and bubble formation. Comparison with literature data reveal the strong dependency of droplet impact behavior on the Weber number as a combination of initial droplet diameter and impact velocity.
[en] Highlights: • Effect of electron donating tendency on electrochemical oxidation of hydroquinone. • DFT quantum chemical and molecular reactivity parameters for the oxidative behavior of hydroquinone molecules. • Influence of pH on the oxidative behavior of hydroquinone compounds. - Abstract: The effect of electron donating tendency on the oxidative behavior of hydroquinone (HQ) on glassy carbon electrode (GCE) at room temperature was studied by means of cyclic voltammetry (CV), differential pulse voltammetry (DPV) and square wave voltammetry (SWV) techniques in aqueous acetonitrile solution. The oxidation potential of HQ shifted to increasingly more negative direction as electron donating tendency increased due to the presence of electron donating substituent's in the benzene ring of hydroquinone moiety. The study was further extended to observe their oxidative behavior with pH. The results showed that an easy oxidation of hydroquinone compounds with the rise in pH. In order to get a proper insight into to an oxidative behavior, the DFT quantum chemical calculation was performed for all hydroquinone molecules at the B3LYP level and by using 6–311++(d, p) basis set. The calculated quantum chemical and molecular reactivity parameters from optimized structures were good agreement with experimental findings.
[en] The dye sunset yellow (SY) forms columnar aggregates via π-π stacking in aqueous solutions. These aggregates develop orientational and translational order at elevated concentrations to exhibit the nematic (N) and columnar (C) mesophases. Positional-order correlation lengths of the aggregates in the directions parallel and perpendicular to the stacking direction were measured as functions of temperature, concentration, and ionic content of solutions with synchrotron x-ray scattering in magnetically aligned samples. Average length of aggregates (i.e., the number of SY molecules in an aggregate) grows monotonically with concentration while their effective transverse separation decreases. The scission energy, E, determined from the Arrhenius thermal evolution of the longitudinal correlation length, is found to be 4.3 ± 0.3 kBT and 3.5 ± 0.2 kBT, in the N and C phases, respectively. Temperature and concentration dependence of E suggests that chromonic aggregation is not an isodesmic process. The aggregate length decreases with decreasing pH when HCl is added to the solution.
[en] Different metal-powders like Cu, Ni and precious metals like Ag, Au, Pt or Pd can be produced by adding a suitable reducing agent to an aqueous metal solution. In some cases it is also possible to produce homogeneous solid solution powders. The particle-sizes can be varied in dependence of the reducing parameters like dilution of the solutions and temperature. Submicron powders far below 1 μm as well as particle-sizes up to 5 μm can be produced. A simultaneous co-precipitation of solutions containing the dissolved metal as well as Zr-, or Y-compounds is possible to obtain ODS-materials thereof. Subsequent conventional PM-processing like sintering with simultaneous transformation into oxides and subsequent deformation produces e.g. Zr-, or Y-oxide stabilized materials with suitable mechanical properties. (author)
[en] On experimental values of propagation speed of ultrasound and density of solution, the concentration dependence of number of hydration cations has been determined. The hydration numbers found taking into account the changes in the adiabatic compressibility of water with increasing salt concentration decrease stepwise. (author)
[en] Equilibrium-constant expressions for Pu disproportionation reactions traditionally contain three or four terms representing the concentrations or fractions of the oxidation states. The expressions can be rewritten so that one of the oxidation states is replaced by a term containing the oxidation number of the plutonium. Experimental estimations of the numerical values of the constants can then be checked in several ways. (author)
[en] Glycerol is used in many applications of science and daily life as it is cheap and biologically non-invasive. In science, aqueous solutions of glycerol are commonly used for experimental investigations as their density can be adapted by changing the glycerol content in the solution. Although the density of aqueous glycerol solutions has been measured precisely since more than a century, current models show a deviation from measured data of up to . In this work we present an analytical expression to accurately calculate the density of aqueous glycerol solutions. The presented empirical model is validated in the range between 15 and and has a maximum deviation of less than with respect to measured data. This improves the accuracy of current models by more than one order of magnitude. By knowing the temperature and glycerol content of the solution, its density can be simply calculated with the presented model. A Matlab function is provided in the supplementary material to allow a simple implementation in other scientific work.