摘要:

AbstractRecent experimental investigations of interfacial wetting phenomena in binary liquid mixtures characterized by Coulomb or screened Coulomb short range interactions are discussed. Wetting transitions occurring at the fluid‐wall and the fluid‐vapour interface are considered focusing on the examples of fluid alkalimetal‐alkalihalide mixtures and liquid gallium‐based binary alloys at elevated temperatures. Different spectroscopic methods have been employed to probe the respective interfaces, spectroscopic ellipsometry and second harmonic generation (SHG). In the case of K‐KCl solutions the SHG results exhibit changes characteristic of a prewetting transition in metalrich solutions implying a first order wetting transition at coexistence. A wetting transition is observed for liquid Ga‐Bi and Ga‐Pb alloys approaching the monotectic point a

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020102

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe excess molar enthalpiesHEmof {xN2O+(1‐x)C7H16} were measured in the liquid and supercritical region covering the whole concentration range. Mixtures at 308.15 K and 7.64, 9.48 and 12.27 MPa show moderately endothermic and exothermic mixing in the heptane‐rich region and nitrous oxide‐rich region, respectively. The exothermic‐mixing region is confined to a smaller range ofxas pressure increases and disappears completely at 308.15 K and 15.00 MPa. Mixtures at 318.15 K and 7.64 and 9.48 MPa show very exothermic mixing. Mixtures at 318.15 K and 12.27 and 15.00 MPa show moderately endothermic and exothermic mixing in the heptane‐rich region and nitrous oxide‐rich region, respectively. The changes observed in the excess enthalpy with temperature and pressure are discussed in terms of liquid‐vapor equilibrium and critical constants for nitrous oxide‐heptane. Excess enthalpies for nitrous oxide‐heptane mixtures are also calculated by means of the Peng‐Robinson equation of state and the resultingHEmvalues are compa

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020103

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractVapour pressures of di‐n‐propylether with 2‐methyl‐1‐propanol, 2‐butanol, and 2‐methyl‐2‐propanol were measured at several temperatures between 278.15 K and 323,15 K by a static method. Excess molar enthalpies and volumes for mixtures of di‐n‐propylether with 2‐methyl‐l‐propanol and 2‐butanol, were also measured atT=298.15 K. Reduction of the vapour pressures to obtain activity coefficients and excess molar Gibbs free energies was carried out by Barker's method. Mixtures containing 2‐butanol and 2‐methyl‐2‐propanol show azeotropy with a minimum boiling temperature.GE,HE, andVE, at 298.15 K, of these mixtures are compared with predictions of the ERAS‐model observing that the model reproduce

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020104

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractSeveral, widely used, group contribution models have been used to predict solid‐liquid equilibria forn‐alcohol+n‐alkane binary mixtures. They are: modified UNIFAC [1], DISQUAC [2, 3], Nitta‐Chao [4] and the Hole Model (HM) [5]. Also a recently reported group contribution model (AssoDis) including association [6] has been taken into account. The results have been compared with experiment

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020105

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe acid‐base equilibria of oxalic, malonic and succinic acids, ethylenediamine, diethylenetriamine and glycine were studied potentiometrically (glass electrode) in NaClO4(for polyamines also in NaCl) solution of various concentrations (0.01‐3 M), at 25°C. The dependence of the change of equilibrium constants with ionic strength on the distance between charge centres in ion is discussed. This dependence more markedly exhibits for ions with the shortest distances between charge centres. No differences in observed effects for different classes of ions were found. The simulation of the medium effects for the systems involving ions with separated charge centres was carried out on the basis of electrostatic notion with the data on the ion structure and the magnitudes of charges on a

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020106

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractMultinuclear spin‐lattice relaxation rates, cross‐relaxation rates and self‐diffusion coefficient measurements are reported over wide ranges of temperature, pressure and concentration in undercooled aqueous solutions of tetraalkylammonium bromides. These dissolved organic cations with apolar surface groups provide model systems to investigate the effect of coulombic, hydrophobic and H‐bond interactions upon the solvent and solute dynamics within the random, transient H‐bond network of undercoo

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020107

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe rate constant and the product distribution of the reaction CH3+OH r̊ products (1) were studied at room temperature over a range of pressures (0.7 mbar ≤p≤467 mbar) with M= He as inert bath gas. At pressures of 45 to 467 mbar, towards the high pressure range of the reaction, experimental determinations were performed using the laser flash photolysis technique with transient UV absorption spectrometry (LFP/TAS) for direct monitoring of the CH3and OH radicals. In this range, the overall rate constant for the reaction was found to be practically independent of pressure atk1(298 K)=(4.4±0.8)x1013cm3mol−1s−1. At pressures of 0.7 mbar to 4.0 mbar, the reaction was studied using the discharge flow (DF) technique with laser magnetic resonance (LMR) for the direct detection of the reactants CH3and OH and the reaction product CH2. The measured overall rate constants at the low pressures were found to increase slightly with increasing pressure and approach the value at “high” pressure from the LFP/TAS experiments. From simulations of the measured concentration‐versus‐time profiles of the CH3, OH, and CH2radicals, the branching ratio for the reaction channel CH3+OHr̊ CH2+H2O (1.1) was determined atp=1.33 mbar,T=298 K to bek1.1lk1=(0.89±0.09). Implications of the results are discussed considering the fall‐off curve for the reaction, the reaction mechanism and the product distribution, and the availabl

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020108

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe reaction of silane with H atomswas studied behind reflected shock waves at temperatures between 998 K and 1273 K and pressures around 1.5 bar. The thermal decomposition of a few ppm ethyl iodide (C2H5I) was used as a well known H‐atom source. The atomic resonance absorption spectroscopy (ARAS) was applied for time resolved and simultaneous measurements of H‐ and Si‐atom concentrations. The presence of an excess of SiH4causes a fast consumption of H atoms according to reaction (R 5). The signals obtained were kinetically evaluated by computer simulations based on a simplified reaction mechanism. The rate coefficient for reaction (R 5) was found to be:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_5 = 7.8 \times 10^{14} \;\exp ( - 2260/T)\;{\rm{cm}}^3 \;{\rm{mol}}^{- 1} \;{\rm{s}}^{- 1}. $$\end{doc

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020109

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractThe kinetics of the reactions of Br(2P3/2) with selected aldehydes, i.e. ethanal (l), propanal (2). 2‐methyl‐pro‐panal (3), 2,2‐dhethyl‐propanal (4) and trichloroacetaldehyde (5) were studied at 298±2 K. Rate constants for overall reactions were measured using the fast flow technique with resonance fluorescence detection of Br. Complementary determinations were carried out by the laser flash photolysis method. The following rate constants were obtained in the kinetic measurements (±2σ): k1=(2.1±0.2)×1012, k2=(4.3±0.4)×1012, k3=(6.3±1.4)×1012, k4=(8.5±0.8)×1012, k5≤1×109all in cm3mol−1s−1units.The probable mechanism for the reactions of bromine atoms with aliphatic a

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020110

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY

摘要:

AbstractHighly concentrated 0.5 M II‐VI semiconductor quantum dot solutions for coating applications can be synthesized employing chalcogenolysis and condensation of functionalized cluster‐like cadmium and zinc ethoxy‐acetates. Furthermore, in nucleation studies on CdSe solutions, new magic clusters between 0.42 and 1.7 nm in size were found exhibiting sharp HOMO‐LUMO resonances (lowest absorption features) in the optical absorption spectra. High resolution small angle X‐ray scattering (SAXS) measurements performed on 1.7 and 3.4 nm CdSe clusters corroborate the size. Information on the intra‐cluster structure was hard to derive with respect to the small cluster size. These species could be Koch pyramids with a fractal dimensionDf=2 as well as non‐fractal zincblende pyramids (additionally checked by XRD and HRTEM). In any case rather chain‐like (Df= 1) aggregates are formed. It further will be shown that in alcoholic CdSe sols the initially nucleated “seeds” are highly reactive. Their sharp HOMO‐LUMO transitions are found to be strongly modified by externally induced chemical reactions. For example, aminosilane capped 1.7 nm clusters decompose rapidly upon exposure to phosphines. After a period of few hours, they begin to re‐grow to their original size or they reorganize to give smaller 0.85 nm subunits depending on the P/N ratio. In contrast, 0.85 nm phosphine‐capped clusters double their size if exposed to amines. The last process liberates cadmium ions into the solution as found in complementary p

ISSN:0005-9021    

DOI:10.1002/bbpc.19981020111

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1998

数据来源: WILEY