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  • Physical Chemistry  (9)
  • Chemical Engineering  (6)
  • Physics  (3)
  • Wiley-Blackwell  (18)
  • BioMed Central
  • Wiley
  • 1
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 2300-2305 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The relative merits of various approaches using computer simulation methods for estimating first-order correction terms to Henry's law in dilute supercritical mixtures are investigated. Three thermodynamic formulations are provided for the calculation of these properties. One method, termed the fluctuation integral approach, requires the explicit calculation of solute-solvent pair correlation functions at the infinite dilution limit, which is a difficult task for simulations given the conflicting demands of both small numbers of solute species (for approximating the infinite dilution limit) as well as the need for large numbers of solute species to improve simulation statistics. A second approach, called the pressure gradient method, does not require the explicit, determination of these solute-solute functions and, as a result, is not as sensitive to the choice of system size and other difficulties associated with establishing an adequate ensemble size and/or number of solute species to be used in the simulations. The third approach uses the exact formulation for the property of interest using Kirkwood-Buff theory. This approach, however, requires all the solute pair correlation functions to be established, making it the most sensitive to issues concerning number of solute species used in the simulations, and so on. An examples is given showing simulation results for these approaches, illustrating their respective strengths and drawbacks.
    Additional Material: 6 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 41 (1995), S. 389-401 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An asymptotic analysis based on Taylor series expansions is used for first-order correction terms to the Henry's law approximation to describe solvation phenomena in multiple solute-multiple solvent systems. The magnitude of these correction terms in solvent systems very near their critical points is of particular concern, as shown in model fluid calculations with the aid of integral equation theory. The results clearly demonstrate that close proximity to the critical point in pure and mixed solvent systems causes the Henry's law approximation to show large errors in predicting solubilities, especially near the critical azeotrope of a mixed solvent system. Theoretical results also show that cross solubility enhancements in a two solutesupercritical solvent system cause cooperative synergism (both solute solubilities are increased relative to the corresponding single solute situations) or reverse synergism (both depressed relative to the single solute situation). It appears to be consistent with the available data. In computer simulations, the solute's infinitely dilute reference state is often used as a basis for describing solute thermodynamic behavior. These simulations are best achieved in the canonical ensemble because of the weak composition dependence of free energies in terms of characteristic variables of this ensemble.
    Additional Material: 9 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 39 (1993), S. 1985-1994 
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Computer simulation results are presented for the residual chemical potential μ1r, local solvent density enhancement Δρloc, and average solute potential energy u1 of a solute molecule immersed in afluid very close to its critical point. The simulation algorithm involves the Monte Carlo method in conjunction with free energy perturbation ideas. A number of ideas related to the feasibility of computer simulations in near-critical solvents are investigated. Due to long-range correlations near the critical point, it is not clear that simulations in this regime can be expected to yield accurate results using ensemble sizes of the magnitude typically used in simulations. Examination of system size and number of sampling steps on the simulations shows that the accuracy of the results depend to a large extent on the nature of the thermodynamic property being investigated. The solute chemical potential is suited particularly to simulation since it depends primarily on short-range structure in the system. A comparison of the simulation results with integral equation theory calculations shows both approaches agree well with each other.
    Additional Material: 7 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 32 (1992), S. 43-48 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A commercial thermotropic polyesteramide and its blends with polyarylate are the object of a slit die flow rheological study. The measurements are carried out at 280°C, a temperature slightly above the melting temperature of the thermotropic, covering a shear rate range 10-1 s-1 to 102s-1. Except in the case of the thermotropic polymer, the pressure profiles are upward parabolic which is attributed to the dependence of the viscosity on pressure. The most striking result is the observed downward curvature in pressure profiles obtained for the liquid crystalline polyesteramide: no explanation is given for this phenomenon, for the present. The elasticity of the polymer melts is expressed in terms of the exit pressure and the extrudate swell. The thermotropic polyesteramide presents negative values of both parameters (e.g. samples shrink instead of swell). Viscosity and elasticity present negative deviation from linearity when plotted against composition; this reduction in the rheological functions, caused by the addition of liquid crystal, is more pronounced at high shear rates.
    Additional Material: 10 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 35 (1997), S. 2379-2384 
    ISSN: 0887-6266
    Keywords: ultrasound degradation ; microwave degradation ; polyamides ; polypeptides ; polyglutamates ; polyaspartates ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: No abstract.
    Additional Material: 4 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 253-263 
    ISSN: 0887-6266
    Keywords: thermotropics ; dynamic viscoelasticity ; relaxation peaks ; gelation ; crystallization ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The rheological characterization of two commercial thermotropic liquid crystalline polymers based on poly(ethylene terephthalate) (PET) and para-hydroxybenzoic acid (PHB) is carried out. The thermal transitions determined by DMTA are explained by the random character of these copolyesters, in comparison with non-random copolyesters synthesized by Jackson and Kuhfuss. The evolution of the dynamic viscoelastic functions with time in the nematic state is concave in shape for the 20%PET/80%PHB copolymer, a result that leads us to treat this system as a suspension of solid spheres (unmolten crystals) where the volume fraction of crystals increases with time according to an Avrami equation. The response of 40%PET/60%PHB copolymer is similar to a chemical or physical gelation and the hypothesis that the polydomain structure gives rise to a network is considered. Continuous flow, time-independent viscosity results reveal the existence of a three-region flow curve for 40%PET/60%PHB copolymer, but a Newtonian zone followed by a shear thinning region for 20%PET/80%PHB sample. At high temperatures the isotropization of the samples leads to a very strong decrease of the activation energy of flow, which becomes zero for 40%PET/60%PHB. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 253-263, 1998
    Additional Material: 10 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 6 (1993), S. 651-659 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The solubility behaviour of β-cyclodextrin in aqueous mixtures was studied by determining the interactions between the co-solvent and water. Three clear classes of co-solvent are evident. In the first, including ethanol, tetrahydrofuran and acetone, there is formation of clathrate hydrates by the co-solvent. In these systems the solubilization is a maximum at the mole fraction corresponding to the minimum in the partial excess molar volume. The second class, including such solvents as dimethyl sulphoxide and pyridine, forms strong molecular complexes with water, and here a valley and a plateau region occur in the solubility values. In the third class, including formamide and urea, a steady increase in the solubility is observed. For these highly polar solvents no maxima are observed in intrinsic solvent properties such as the partial excess molar volume.
    Additional Material: 6 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Chichester : Wiley-Blackwell
    Journal of Physical Organic Chemistry 8 (1995), S. 559-562 
    ISSN: 0894-3230
    Keywords: Organic Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The monocation-dication equilibria of 6-nitro and 6-sulphonic acid derivatives of betacarboline (9H-pyrido[3,4-b]indole) were investigated mostly by UV-visible absorption spectroscopy. Dications are formed in very highly concentrated sulphuric acid solutions (〉15 M). Ionization constants, pKa values and solvation parameters obtained from the excess acidity method are reported. The unusually high m* parameters are discussed and compared with other related data.
    Additional Material: 1 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 25 (1985), S. 188-191 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Rheological and processing parameters have been measured for a commercial polystyrene at temperatures from 155°C to 210°C resulting in no clear evidence for the existence of liquidliquid transition. Zero shear viscosities obtained from dynamic measurements and ends corrections and extrudate swell from capillary rheometry are analyzed, with the conclusion that the mechanism of flow is the same throughout the range of temperatures considered.
    Additional Material: 4 Ill.
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 27 (1995), S. 987-995 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The reactions of the title substrates with a series of secondary alicyclic amines are subjected to a kinetic study in 44 wt% aqueous ethanol, at 25.0deg;C, ionic strength 0.2 M (maintained with KCl). Pseudo-first-order kinetics are found under amine excess. The order in amine obtained is one in the reactions of all amines. The Brönsted-type plots for the overall second-order rate coefficients are biphasic with slopes β1 = 0.3 (high pKa), β2 = 0.95 (low pKa) for the aminolysis of the 4-nitro derivative, and β1 = 0.3 and β2 = 0.80 for the aminolysis of the dinitro compound; the pKa values at the curvature center are pKa0 = 9.8 and 9.5, respectively. From a comparison of these pKa0 values with those found in the same reactions in water and the shapes of the Brönsted-type plots, it is concluded that these reactions are stepwise, with the formation of a zwitterionic tetrahedral intermediate in the reaction pathway. © 1995 John Wiley & Sons, Inc.
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