Membrane separation of gaseous C1-C4 alkanes

The separation of various gaseous hydrocarbons with the aid of polymer membranes is considered; attention is focused on the separation of gaseous C₁–C₄ alkanes, which are the components of natural gas and associated petroleum gases. It is noted that a practically important property of membrane materials is the thermodynamic selectivity of a membrane, which makes it possible to enrich a permeate with heavier alkanes. Up to this point, polyacetylenes exhibited the best transport parameters for the solution of this problem. The second experimental section of this paper describes a study of the separation of CH₄ + C₄H₁₀ binary mixtures on films based on additive poly[3-(trimethylsilyl)tricyclononene-7]. It is demonstrated that this highly permeable saturated glassy polymer exhibits thermodynamic selectivity in experiments with both the individual gases (CH₄ and C₄H₁₀) and their mixtures and provides fivefold butane enrichment of a permeate. The test polymer and others additive Si-containing norbornene polymers are of interest as membrane materials for the separation of hydrocarbon gases.     

Solution study of novel diblock copolymers: Morphology and structural transition

The solution behavior and morphology of the nanostructures formed by novel block copolymers based on 1-cetyl[2-(acryloyloxy)ethyl]dimethylammonium bromide (ADHA) and 2-hydroxyethylacrylate (HEA) or N-isopropylacrylamide (NIPAM) have been studied using small angle X-ray scattering (SAXS), dynamic light scattering (DLS), and transmission electron microscopy (TEM). In these block copolymers the pADHA block consists of long hydrophobic C₁₆ tails connected to a positively charged quaternary ammonium group, making it amphiphilic, while the second block is either fully hydrophilic (pHEA) or thermoresponsive (pNIPAM). Using SAXS, we demonstrate that the morphology of block copolymer nanostructures is dependent on the solute concentration and on the length and composition of the blocks. In the case of thermoresponsive pADHA-b-pNIPAM, two types of ordered structures are formed and their characteristics are also defined by the temperature. Complementary information is obtained from DLS, showing large particles with the size up to 280 nm, which is beyond the resolution of the SAXS data. Loss of ordering around the lower critical solution temperature followed by ordering restoration at the higher temperature was observed for the pADHA-b-pNIPAM block copolymers. The differences in the structural order in the block copolymer solutions are directly related to their ability to coat hydrophobic metal nanoparticles.     

HYDROTHERMAL SYNTHESIS AND CHARACTERIZATION OF THE LAYERED ZHRCONIUM GERMANATE Na2Zr5Ge2O15-nH2O

ABSTRACT

A layered sodium zirconium germanate of formula Na2ZrsGe20iS-nH20 isostructural to the layered Na₂Zr₅Si₂O₁₅-nH₂O and Zr₂O₃(H₂O₄) ( ψ -zirconium phosphate) was synthesized hydrothermally. Its protonic form H₂Zr₅Ge₂O₁₅nH₂O was prepared by acid treatment of the initial compound. The properties of these compounds were determined by means of physical and chemical methods, including X-ray diffraction, thermal analysis, Qt and scanning electron microscopy The layered nature of the compound was confirmed by amine intercalation reactions. The ion exchange behavior of the zirconium germanate towards alkali and alkaline-earth ions was studied over a wide pH range (2-14) by the batch technique.     

Protected bis(hydroxyorganyl) polysulfides as modifiers of Li/S battery electrolyte

The protected bis(hydroxyorganyl) polysulfides synthesized have been tested as modifiers of electrolyte of lithium-sulfur rechargeable batteries. The best result (35% increase of the battery capacity at the 50th cycle) was attained using 5 wt.% of 2,2,12,12-tetramethyl-4,10-diphenyl-3,11-dioxa-6,7,8-trithia-2,12-disilatridecane. Bis(hydroxyorganyl) polysulfides protected at the hydroxyl group have been synthesized for the first time by the reaction of oxiranes with sodium polysulfide (ethanol, NaHCO₃, 12 h, 20–25 °C) in yield 21–87%. For the hydroxyl protection in the hydroxy polysulfides, the acetal, tri(methyl)silyloxy or tri(ethoxy)silyl protecting groups were employed.     

Extended H2 photoproduction by N2-fixing cyanobacteria immobilized in thin alginate films

Screening of the University of Helsinki Culture Collection for naturally good H₂ producing cyanobacteria recently revealed several promising strains. One of the superior strains is Calothrix 336/3, an N₂-fixing heterocystous filamentous cyanobacterium. Making use of an important feature of the Calothrix 336/3 cells to adhere to the substrate, we applied an immobilization technique to improve H₂ production capacity of this strain. We examined the basic properties of immobilization in Ca²⁺-alginate films in response to the production of H₂ of the Calothrix 336/3 strain and as reference strains we used a model organism Anabaena PCC 7120 and its uptake hydrogenase mutant, ΔhupL, that allow us to compare the responses of different strains to alginate entrapment. Immobilization of the Calothrix 336/3 and ΔhupL mutant cells in Ca²⁺-alginate resulted in prolonged H₂ production over several cycles. Immobilization of the Calothrix 336/3 cells was most successful and production of H₂ could be measured even after 40 days after immobilization.     

Surfactant Effect on the Average Flow Generation Near Curved Interface

The present work is devoted to the average flow generation near curved interface with a surfactant adsorbed on the surface layer. The investigation was carried out for a liquid drop embedded in a viscous liquid with a different density. The liquid flows inside and outside the drop are generated by small amplitude and high frequency vibrations. Surfactant exchange between the drop surface and the surrounding liquid is limited by the process of adsorption-desorption. It was assumed that the surfactant is soluble in the surrounding liquid, but not soluble in the liquid drop. Surrounding liquid and the liquid in the drop are considered incompressible. Normal and shear viscous stresses balance at the interface is performed under the condition that the film thickness of the adsorbed surfactant is negligible. The problem is solved under assumption that the shape of the drop in the presence of adsorbed surfactant remains spherical symmetry. The effective boundary conditions for the tangential velocity jump and shear stress jump, describing the above generation have been obtained by matched asymptotic expansions method. The conditions under which the drop surface can be considered as a quasi-solid are determined. It is shown that in the case of the significant effect of surfactant on the surface tension, the dominant mechanism for the generation is the Schlichting mechanisms under vibrations.     

Effects of Mixture Components on Sialon Composition Homogeneity on Synthesis from Kaolins

Carbothermal reduction has been combined with nitriding of kaolin with various free SiO₂ contents in the presence of additional silicon-bearing components under experimental industrial conditions to make β-sialons with Z = 0.73-3.78. It is possible to make a sialon with a given Z by means of additional silicon-bearing components, and also a sialon with Z = 2 directly from raw material kaolin. X-ray diffraction indicates that the composition inhomogeneity in the sialon is dependent on the content of free SiO₂ in the mixture.     

Gas-Sprayed Tin Powders

A gas-dynamic technology has been developed for obtaining tin powder by spraying molten metal and equipment has been built for this purpose. The powder (grain size <100 m) is distinguished by the stability of its parameters, including the granulometric composition. This is achieved by keeping the technological parameters stable throughout the metal spraying process. Those parameters have been calculated and then refined on the basis of results obtained from experimental research on the process of spraying liquid metal. A constant molten metal consumption is ensured by a special dosing device. Its design and operation are described and the parameters of the powders produced are given.     

Confocal Annular Josephson Tunnel Junctions with Large Eccentricity

Confocal annular Josephson tunnel junctions (CAJTJs), which are the natural generalization of the circular annular Josephson tunnel junctions, have a rich nonlinear phenomenology due to the intrinsic non-uniformity of their planar tunnel barrier delimited by two closely spaced confocal ellipses. In the presence of a uniform magnetic field in the barrier plane, the periodically changing width of the elliptical annulus generates a asymmetric double-well for a Josephson vortex trapped in a long and narrow CAJTJ. The preparation and readout of the vortex pinned in one of the two potential minima, which are important for the possible realization of a vortex qubit, have been numerically and experimentally investigated for CAJTJs with the moderate aspect ratio 2:1. In this work, we focus on the impact of the annulus eccentricity on the properties of the vortex potential profile and study the depinning mechanism of a fluxon in more eccentric samples with aspect ratio 4:1. We also discuss the effects of the temperature-dependent losses as well as the influence of the current and magnetic noise.     

Effects of Solution History on Sol‐Gel Processed Tin‐Oxide Thin‐Film Transistors

Antimony‐doped tin‐oxide (SbTO) thin films deposited by solution processing methods represent a promising avenue toward low‐cost transparent and flexible electronics, but reproducibility and performance homogeneity of devices prepared from these thin films have been seldom investigated. In this study, the role of sol‐gel precursor aging is investigated by comparing SbTO thin‐film transistors (TFT) fabricated from two different sol‐gel solutions: the first one was aged for 4 years, whereas the second was prepared freshly. For each of the solutions, a set of TFT was assembled on the same chip, to investigate the distinct roles of aging and sample inhomogeneity on the electronic and transport properties of SbTO. Higher electron mobility, but lower on/off ratios, was found in TFTs assembled from freshly prepared solution, an effect that may be assigned to larger size of SbTO grains. This study demonstrates the critical role of the solution “history” in determining the properties and reproducibility of SbTO TFTs, over other factors, including local film inhomogeneity and local fluctuations of the annealing temperature.