Vapor pressure isotope effects in aqueous systems. VIII. The system dimethyl sulfoxide/H2O/D2O

Vapor pressures for the system I (dimethyl sulfoxide/H₂O=DMSO/H₂O) and isotopic differential pressures I-II (II=DMSO/D₂O) have been measured between 25 and 70°C at DMSO concentrations of 0.05, 0.15, 0.30, 0.45, 0.60, 0.70, 0.80, 0.87, and 0.92 mole fraction. A high-precision differential method was used. The total pressures over the solutions, I, have been fitted to a relation derived from the Duhem-Margules equation, P ^T =P ₁ ^o X₁γ₁+P ₂ ^o X₂γ₂, with γ₁=exp[∑_kα_kX ₂ ^k ] and $$\gamma _2 = exp[\sum \alpha _k X_2^k - \sum (\alpha _k /(k - 1))(kX_2^{k - 1} - 1)].$$ . The α_k are parameters andk is a number ≥2. The α_k were taken as temperature dependent. Four parameters sufficed to fit the data within experimental error. Excess partial molal properties derived from the fits are in quantitative agreement with earlier literature results derived from the directly measured partial pressures, but the present data extend over a wider temperature range. The isotopic differential pressures I-II were similarly fitted to the relation above. The excess free energies and enthalpiesG _I ^E andH _I ^E are large and negative. The isotope effects ΔG _I,II ^E =G _I ^E ?G _II ^E and ΔH _I,II ^E are negative. They are discussed in detail in terms of the theory of isotope effects in condensed phases and demonstrated to be consistent with that theory and with the available spectroscopic data. A small amount of enthalpy data for the solution of DMSO in HOH and DOD is reported.     

Equilibrium isotope effects in aqueous systems. IV. The vapor pressures of NaBr,Nal, KF,Na2SO4, and CaCl2 solutions in H2O and D2O (O to 90°C). Vapor pressures of Na2SO4·10H2O, ·10D2O and CaCl2·2H2O, ·2D2O

Solvent vapor pressure isotope effects have been measured in HOH/DOD between approximately 0 and 90°C on the following electrolyte solutions: NaBr (2, 5, 7, and 9m), NaI (4, 6, 8, and 10m), KF (3, 6, 9, and 12m), Na₂SO₄ (2m and saturated solutions, and hydrated cyrstal), and CaCl₂ (3, 5.5, 8, and 10m, and hydrated crystal). Values of the isotope effects on the various excess thermodynamic properties of solution, including the osmotic and activity coefficients and the excess free energies, enthalpies, and entropies, have been extracted from least-square expressions which fit the VPIE over the entire concentration and temperature range. The results are compared with those obtained for alkali metal chloride solutions (I, II) and literature data where possible. They are discussed briefly in terms of solution structure.     

Continuity of solvent quality in polymer solutions. Poor-solvent to Θ-solvent continuity in some polystyrene solutions

Critical temperatures for polystyrene/methyl acetate (PS/MA) and polystyrene/ethyl formate (PS/EF) solutions were measured at positive (PS/MA, PS/EF) and negative (PS/MA) pressure. The results confirm that solvent quality is sensitive to pressure; some solvents, designated Θ, at P_nominal ∼ 0, undergo a Θ-to-poor transition at negative pressure, and others, nominally designated “poor,” show a poor-to-Θ transition at positive pressure. Thus, any dichotomous division into sets of “poor” and “Θ” solvents is inaccurate, unless it accounts for the effects of pressure and other variables on solvent quality. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1251–1259, 1997     

The Use of Phosphine as an Agricultural Fumigant

Abstract

Problems associated with using a phosphine /CO₂ mixture as a fumigant include oxidation and contamination with P₄     

79Br NMR spectroscopy as a practical tool for kinetic analysis

⁷⁹Br NMR spectroscopy has been used to monitor a series of reactions in which the bromide ion is produced, including the Menschutkin reaction of pyridine with a range of substituted benzyl bromides and a Heck coupling process. In cases where the process could also be monitored using ¹H NMR spectroscopy, the kinetic analyses using heteronuclear magnetic resonance spectroscopy were shown to be completely consistent. Both the utility of the process in following reactions which may be difficult to analyse using other techniques and the practical limitations associated with solvent choice are discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Pressure dependence of the second virial coefficient of dilute polystyrene solutions

The pressure derivatives of the second virial coefficients [dA₂/dP; 0.1 ≤ P (MPa) ≤ 35.0] for dilute polystyrene (PS) solutions in good, θ, and poor solvents were measured with static light scattering. The solvent quality improved (dA₂/dP > 0) in the good and poor solvents that we investigated (toluene, chloroform; and methylcyclohexane) but deteriorated (dA₂/dP < 0) in θ solvents (cyclohexane and 50‐50 cis,trans‐decalin). The effects of temperature [22 < T (°C) < 45] and molecular weight [25 × 10³ < weight‐average molecular weight (amu mol^?1) < 900 × 10³] on dA₂/dP for PS/cyclohexane solutions were examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3070–3076, 2003     

Intersubband resonance polarons in Al/δ-GaAs tunneling junctions

Tunneling spectra of the A1/δ-GaAs junctions fabricated by molecular-beam epitaxy in the regime of “intimate” contact of A1 with GaAs (100) were studied at 1.6 K in a magnetic field B parallel to the two-dimensional electron-gas layer. The concentration of 2D electrons in the δ-layer grown at a distance of 20 nm from the A1/GaAs interface was 1.1 × 10¹² cm^?2 and corresponded to a partial filling of only the lowest subband E ₀. The tunneling spectra exhibited many-particle features, viz., a zero-bias anomaly, lines of longitudinal optical (LO) phonons, and characteristic “dips” corresponding to the energies E _i of the 2D subbands. In the B fields below the critical value B _c ?11 T, the levels of 2D subbands underwent the usual diamagnetic shifts. At B≥B _c , the E ₁ (B) term pinning and the anticrossing of the E ₁(B) and E ₀(B)+2?ω_LO terms were observed, where ?ω_LO is the LO-phonon energy in GaAs. The observed effects are interpreted as manifestations of resonance intersubband polarons arising in the δ-layer upon reaching the E ₁(B _c )?E ₀(B _c )=2?ω_LO resonance.