Photochemical (2+2)-cycloaddition of thioxanthenethione with some butatriene derivatives

Irradiation of thioxanthenethione $\text{1}$ with the alkyl- and alkoxysubstituted butatrienes $\text{2}$a-d gives the thietanes $\text{3}$a-d the cyclobutanethione $\text{6}$ is formed as a byproduct. Free radical addition of iC₃H₇SH to $\text{2}$a predominantly occurs via terminal attack of the thiyl radical on the π-system.     

Multivariate data analysis for x-ray fluorescence spectrometry

A multivariate data analysis procedure that uses singular value decomposition and the Ho-Kashyap algorithm is proposed to obtain calibration constants for x-ray fluorescence spectrometry. These calibration constants can be used to obtain results from experimental data by means of a simple dot product calculation. The method was tested on experimental data from the literature. Comparison of results showed that the method performs at least as well or better than the Rasberry-Heinrich method or its modifications. The method can be used to express calibration results obtained with a theoretically based program in such a way that they can be used conveniently in routine applications.     

Infrared determination of unsaturated bonds in polyethylene

Summary A method is presented for the determination of the degree of unsaturation of polyethylene samples by means of infrared spectroscopy. The required extinction coefficients for the vinyl, vinylidene and transvinylene absorption bands, at 910, 885 and 963 cm^–1 resp. are determined on films prepared from mixtures of suitable unsaturated hydrocarbons with n-hexatriacontane or polyethylene. The degree of unsaturation found is in perfect agreement with ICl-titration data.

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Zusammenfassung Eine Methode zur Bestimmung des Grades der Ungesättigtheit von Polyäthylenproben durch IR-Spektroskopie wird vorgeschlagen. Die gesuchten Extinktionskoeffizienten für die Vinyl-, Vinyliden- und trans- Vinylen-Absorptionsbanden bei 910, 885, und 963 cm^–1 werden auf Filmen bestimmt, die aus Gemischen entsprechender ungesättigter Kohlenwasserstoffe mit n-Hexatriacontan oder Polyäthylen hergestellt werden.Der gefundene Grad der Ungesättigtheit stand in bester Übereinstimmung mit den nach der JCl-Methode gefundenen Werten.

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A preliminary publication on this subject has appeared in Polymer Letters 2, 339 (1964).     

Facile Surfactant‐Free Synthesis of p‐Type SnSe Nanoplates with Exceptional Thermoelectric Power Factors

A surfactant‐free solution methodology, simply using water as a solvent, has been developed for the straightforward synthesis of single‐phase orthorhombic SnSe nanoplates in gram quantities. Individual nanoplates are composed of {100} surfaces with {011} edge facets. Hot‐pressed nanostructured compacts (E_g≈0.85 eV) exhibit excellent electrical conductivity and thermoelectric power factors (S²σ) at 550 K. S²σ values are 8‐fold higher than equivalent materials prepared using citric acid as a structure‐directing agent, and electrical properties are comparable to the best‐performing, extrinsically doped p‐type polycrystalline tin selenides. The method offers an energy‐efficient, rapid route to p‐type SnSe nanostructures.     

Noncontinuous froude number scaling for the closure depth of a cylindrical cavity

A long, smooth cylinder is dragged through a water surface to create a cavity with an initially cylindrical shape. This surface void then collapses due to the hydrostatic pressure, leading to a rapid and axisymmetric pinch-off in a single point. Surprisingly, the depth at which this pinch-off takes place does not follow the expected Froude(1/3) power law. Instead, it displays two distinct scaling regimes separated by discrete jumps, both in experiment and in numerical simulations (employing a boundary integral code). We quantitatively explain the above behavior as a capillary wave effect. These waves are created when the top of the cylinder passes the water surface. Our work thus gives further evidence for the nonuniversality of the void collapse.     

System peaks and their positive and negative aspects in chromatographic techniques

Whenever a mobile phase contains more than one component, additional signals commonly called system peaks can appear. The origin of these signals is explained through loss of equilibrium in the separation column caused by injection of analyte dissolved in a different solvent than the mobile phase. The system peaks are then generated by a relaxation process started by the non-equilibrium state. An overview of the theory and applications of the system peaks in separation methods, mainly in liquid chromatography, is presented in this paper. Only a brief theoretical discussion of the system peak origin is given as the theoretical aspects of system peak formation have already been published in many papers. The main focus of this review is to summarize applications, in which system peaks were used to measure physical or physicochemical data. Signals of system peaks are often misinterpreted but they offer valuable information about thermodynamics and kinetics of the separation process that takes place in chromatographic column.     

Suppression of CO2-plasticization by semiinterpenetrating polymer network formation

CO₂-induced plasticization may significantly spoil the membrane performance in high-pressure CO₂/CH₄ separations. The polymer matrix swells upon sorption of CO₂, which accelerates the permeation of CH₄. The polymer membrane looses its selectivity. To make membranes attractive for, for example, natural gas upgrading, plasticization should be minimized. In this article we study a polymer membrane stabilization by a semiinterpenetrating polymer network (s-ipn) formation. For this purpose, the polyimide Matrimid 5218 is blended with the oligomer Thermid FA-700 and subsequently heat treated at 265°C. Homogeneous films are prepared with different Matrimid/Thermid ratios and different curing times. The stability of the modified membrane is tested with permeation experiments with pure CO₂ as well as CO₂/CH₄ gas mixtures. The original membrane shows a minimum in its permeability vs. pressure curves, but the modified membranes do not indicating suppressed plasticization. Membrane performances for CO₂/CH₄ gas mixtures showed that the plasticizing effect indeed accelerates the permeation of methane. The modified membrane clearly shows suppression of the undesired methane acceleration. It was also found that just blending Matrimid and Thermid was not sufficient to suppress plasticization. The subsequent heat treatment that results in the s-ipn was necessary to obtain a stabilized permeability. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1547–1556, 1998     

Thermoplastic composites based on flax fibres and polypropylene: Influence of fibre length and fibre volume fraction on mechanical properties

Natural-fibre-mat-reinforced thermoplastic (NMT) composites based on flax fibre mats and a Polypropylene (PP) matrix were manufactured using (i) a film-stacking method and (ii) a paper making process. The influence of fibre length and fibre content on stiffness and strength is reported and compared with data for glass-mat-reinforced thermoplastic (GMT) composites, including the influence of using maleic-anhydride grafted PP. The data is also compared with existing micromechanical models like Kelly-Tyson and Cox-Krenchel for strength and stiffness, respectively. A good agreement was found between theory and experiment in case of stiffness while in case of strength the experimental values fall well below the theoretical predictions. Results indicated that NMTs are of interest for low-cost engineering applications and can compete with commercial GMTs, especially when a high stiffness per unit weight is desirable. Results also indicated that the key area for future development lies not only in improved adhesion but mainly in improving the fibre strength.     

Fractional-Flow Theory for Non-Newtonian Surfactant-Alternating-Gas Foam Processes

Transport in Porous Media - Foam can improve sweep efficiency in gas-injection-enhanced oil recovery. Surfactant-alternating-gas (SAG) is a favored method of foam injection. Laboratory data...