Hypercrosslinked Additives for Ageless Gas‐Separation Membranes

The loss of internal pores, a process known as physical aging, inhibits the long‐term use of the most promising gas‐separation polymers. Previously we reported that a porous aromatic framework (PAF‐1) could form a remarkable nanocomposite with gas‐separation polymers to stop aging. However, PAF‐1 synthesis is very onerous both from a reagent and reaction‐condition perspective, making it difficult to scale‐up. We now reveal a highly dispersible and scalable additive based on α,α′‐dichloro‐p‐xylene (p‐DCX), that inhibits aging more effectively, and crucially almost doubles gas‐transport selectivity. These synergistic effects are related to the intimately mixed nanocomposite that is formed though the high dispersibility of p‐DCX in the gas‐separation polymer. This reduces particle‐size effects and the internal free volume is almost unchanged over time. This study shows this inexpensive and scalable polymer additive delivers exceptional gas‐transport performance and selectivity.     

The structure of bis(trialkyltin) carbonates: Evidence for two non-equivalent tin sites

Bis(tributyltin) oxide or trimethyltin hydroxide react with carbon dioxide to afford the bis(trialkyltin) carbonates, (R₃SnO)₂CO; ¹¹⁹Sn NMR (in the case of R = Bu) or ^119mSn Mössbauer spectroscopy show that these compounds contain 4- and 5-coordinate tin atom sites.     

Chemical process optimization by computer — a self-directed chemical synthesis system

A closed-loop automated chemical synthesis system has been designed for the purpose of optimizing chemical reaction parameters. This system uses a time-sharing computer with the simplex algorithm for optimization programmed in extended BASIC language. Strings of ASCII characters from the computer are trapped by terminal hardware at the reaction and analysis sites and are used to control all phases of the system.     

Thermal properties of molten sulphur-oxyanionic salts

Lithium, sodium, potassium and ammonium bisulphate have been shown by detailed TG/DTA studies to have limited application as molten solvents. By contrast, the eutectic bisulphate systems, ammonium-potassium bisulphate and sodium-potassium bisulphate, appear to be excellent molten solvents in view of their low melting points, long liquid ranges and prolonged thermal stability at 200°. In contrast to previous studies, potassium pyrosulphate has been found to be an excellent molten solvent, provided rigorous preliminary drying procedures have been applied.

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Zusammenfassung An Hand eingehender TG/DTA-Untersuchungen wurde gezeigt, daß die Bisulfate von Lithium, Natrium, Kalium und Ammonium nur eine begrenzte Anwendung als geschmolzene Lösungsmittel finden können. Die eutektischen Bisulfat-Systeme Ammonium/ Kalium Bisulfat und Natrium/Kalium Bisulfat scheinen wegen ihrer niedrigen Schmelzpunkte, ihres weiten Flüssigkeitsbereichs und ihrer dauerhaften Thermostabilität bei 200° ausgezeichnete geschmolzene Lösungsmittel zu sein. Im Gegensatz zu früheren Untersuchungen erwies sich Kaliumpyrosulfat als ein ausgezeichnetes geschmolzenes Lösungsmittel, vorausgesetzt daß vorangehend strenge Trocknungsverfahren angewandt wurden.

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Résumé On montre par une étude TG/ATD approfondie que les hydrogénosulfates de lithium, de sodium, de potassium et d'ammonium n'ont qu'une application limitée en tant que solvants fondus. Les systèmes eutectiques des hydrogénosulfates ammonium/potassium et sodium/potassium paraissent, au contraire, être des solvants fondus excellents, en raison de leurs points de fusion bas, de leurs larges intervalles d'existence à l'état liquide et de leur stabilité thermique prolongée à 200°. Contrairement à des études antérieures, on a trouvé que le pyrosulfate de potassium est un solvant fondu excellent, à la condition d'appliquer un mode opératoire rigoureux lors du séchage préliminaire.

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The authors would like to thank Dr. C. Barraclough and Mr. M. Beyer of the Physical Chemistry Department, Melbourne University, for assistance with the Raman spectra.     

High-performance liquid chromatographic column-switching technique for the determination of intermediates of anaerobic degradation of toluene in ground water microcosm.

A reversed-phase liquid chromatographic column-switching system was used for the determination of phenol, benzoic acid and cresol (PBC) in the presence of toluene in ground water microcosm. A precolumn was connected in series with an analytical column via a column-switching valve. After the injection, as soon as PBC were eluted from the precolumn to the analytical column, the valve was switched so that the precolumn was between the analytical column and the UV detector. Toluene and other non-polar compounds were eluted from the precolumn in a very short time and detected along with the solvent front. Subsequently, PBC were separated on the analytical column and passed through the precolumn one more time before being detected by the UV detector. The total analysis time was 15 min. This technique facilitated the study of the basic mechanism and path way of anaerobic degradation of toluene in ground water aquifer.     

Electron–nucleus interactions in highly doped rare earth phosphate glasses

³¹P NMR measurements have been used to study the dynamics of magnetic rare earth ions in the stable metaphosphate systems (R₂O₃)_x(X₂O₃)_0.25-x(P₂O₅)_0.75, with R≡Er³⁺, Nd³⁺ and Gd³⁺, for varying concentrations x, where X denotes a nonmagnetic rare earth buffer. Broad EPR spectra are observable at liquid helium temperatures but it is not possible to measure the paramagnetic relaxation time directly. Electronic relaxation parameters and crystal field splittings have been inferred from the NMR relaxation data. Nuclei situated near paramagnetic ion sites experience shifts in resonance frequency due to the local field produced by the ion. The nuclear resonance line is inhomogeneously broadened with decreasing temperature and disappears abruptly at temperatures which depend on the magnetic ion present, its concentration and the magnitude of the applied magnetic field. A discussion of the line broadening process is presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Inverted electron-hole alignment in InAs-GaAs self-assembled quantum dots

New information on the electron-hole wave functions in InAs-GaAs self-assembled quantum dots is deduced from Stark effect spectroscopy. Most unexpectedly it is shown that the hole is localized towards the top of the dot, above the electron, an alignment that is inverted relative to the predictions of all recent calculations. We are able to obtain new information on the structure and composition of buried quantum dots from modeling of the data. We also demonstrate that the excited state transitions arise from lateral quantization and that tuning through the inhomogeneous distribution of dot energies can be achieved by variation of electric field.     

Photocurrent spectroscopy of InAs/GaAs self-assembled quantum dots: observation of a permanent dipole moment

The nature of the confined electronic states in InAs/GaAs self-assembled quantum dots is studied using photocurrent spectroscopy measured as a function of applied electric field. A field asymmetry of the quantum confined Stark effect is observed, consistent with the dots possessing a permanent dipole moment. The sign of this dipole indicates that for zero field the hole wave function lies above that of the electron, in disagreement with the predictions of all recent calculations. Comparison with a theoretical model demonstrates that the experimentally determined alignment of the electron and hole can only be explained if the dots contain a non-zero and non-uniform Ga content.     

High-resolution stimulated Raman spectroscopy of O2

High-resolution (0.002 cm^?1) stimulated Raman spectroscopy has been applied to the study of both normal and satellite Q branches of the fundamental vibrational band of molecular oxygen. Using a pulsed molecular free-expansion jet to adiabatically cool the oxygen sample, satellite Q branches at 1554 and 1558 cm^?1 that arise due to the splitting of the ³Σ_g ground state by spin-spin and spin-rotation interactions were completely resolved for the first time. Measured intensity ratios for the ${}^{\mathrm{<mtext>\Delta </mtext><mtext>N</mtext>}}\text{Δ}\text{J(J, N) =}{}^{\mathrm{Q}}\text{0(2, 1)}$ and ^QR(1, 1) lines, and for the ^QS(0, 1) and ^QP(2, 1) lines compare favorably with that for a coupling case intermediate between Hund's cases (a) and (b). Depolarization ratios, measured for a series of ^QQ-branch (unresolved) triplets, give a value 0.164 ± 0.004 for the depolarization ratio of the fundamental vibrational band.