Wet‐phase‐separation membranes from the polysulfone/N,N‐dimethylacetamide/water ternary system: The formation and elements of their structure and properties

Asymmetric and porous polysulfone (PSf) membranes were prepared by wet phase separation. Binary (PSf)/N,N‐dimethylacetamide (DMA) solutions with polymer concentrations of 12.5–30 wt % were cast in thicknesses of 80–700 μm and immersed in a coagulation bath of pure water. The morphology of the formed membranes' cross sections consisted of a cellular structure and macrovoids; the cellular structure density was highest when the cast solution contained about 21 wt % PSf, regardless of the cast thickness. The membranes' pure water permeability decreased as the cast thickness increased. The instantaneous onset of the turbidity, regardless of the PSf content and cast thickness, its steep growth, and relatively high end value were the main characteristics of the turbidity phenomena taking place during the formation of the protomembranes. Again, the membrane‐forming system with a PSf/DMA solution with about 21 wt % polymer, regardless of the cast thickness, had the highest turbidity end value. The shrinkage of the cast solutions into the corresponding protomembrane was also examined quantitatively. Inverse experiments showed that the direction of the gravitation field had no influence on the shrinkage of the membrane‐forming ternary system or the membranes' morphology and its water permeability. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1667–1674, 2005     

Poly(vinyl acetate) and Poly(vinyl propionate) Star Polymers via Reversible Addition Fragmentation Chain Transfer (RAFT) Polymerization

Summary Poly(vinyl acetate) and poly(vinyl propionate) star polymers with four arms were produced via reversible addition fragmentation chain transfer (RAFT) polymerization, employing a tetra-functional xanthate as the RAFT agent, in which the stabilizing groups are linked to the core. These novel star-like RAFT agents induced living/controlled behavior in both the vinyl acetate polymerization at 60 °C and in the vinyl propionate polymerization at 90 °C, respectively, leading to star polymers with minimum polydispersities of 1.2 and maximum apparent number average molecular weights of about 50,000 g·mol^-1. The microstructure of the star polymers was confirmed by electrospray ionization mass spectrometry.     

Defect induced changes on the excitation transfer dynamics in ZnS/Mn nanowires

Transients of Mn internal 3d⁵ luminescence in ZnS/Mn nanowires are strongly non-exponential. This non-exponential decay arises from an excitation transfer from the Mn ions to so-called killer centers, i.e., non-radiative defects in the nanostructures and is strongly related to the interplay of the characteristic length scales of the sample such as the spatial extensions, the distance between killer centers, and the distance between Mn ions. The transients of the Mn-related luminescence can be quantitatively described on the basis of a modified Förster model accounting for reduced dimensionality. Here, we confirm this modified Förster model by varying the number of killer centers systematically. Additional defects were introduced into the ZnS/Mn nanowire samples by irradiation with neon ions and by varying the Mn implantation or the annealing temperature. The temporal behavior of the internal Mn²⁺ (3d⁵) luminescence is recorded on a time scale covering almost four orders of magnitude. A correlation between defect concentration and decay behavior of the internal Mn²⁺ (3d⁵) luminescence is established and the energy transfer processes in the system of localized Mn ions and the killer centers within ZnS/Mn nanostructures is confirmed. If the excitation transfer between Mn ions and killer centers as well as migration effects between Mn ions are accounted for, and the correct effective dimensionality of the system is used in the model, one is able to describe the decay curves of ZnS/Mn nanostructures in the entire time window.     

Chemical Validation of DegS As a Target for the Development of Antibiotics with a Novel Mode of Action

Despite the availability of hundreds of antibiotic drugs, infectious diseases continue to remain one of the most notorious health issues. In addition, the disparity between the spread of multidrug-resistant pathogens and the development of novel classes of antibiotics exemplify an important unmet medical need that can only be addressed by identifying novel targets. Herein we demonstrate, by the development of the first in vivo active DegS inhibitors based on a pyrazolo[1,5-a]-1,3,5-triazine scaffold, that the serine protease DegS and the cell envelope stress-response pathway σE represent a target for generating antibiotics with a novel mode of action. Moreover, DegS inhibition is synergistic with well-established membrane-perturbing antibiotics, thereby opening promising avenues for rational antibiotic drug design.     

Grinding in an air classifier mill — Part I: Characterisation of the one-phase flow

In this and the related second paper [1], we present an in-depth study of the two-phase flow and the stressing conditions of particles in an air classifier hammer mill. This type of mill belongs to the mostly used mills at all. In order to develop a predictive grinding model not only the material's reaction to the applied stress but also the stressing conditions within the mill, e.g. impact velocity, incidence angle, number of stress events, have to be known. The latter are strongly affected by the interactions between the fluid and the solid phase within the mill. Systematic flow investigations in the vicinity of the impact elements and in the region of the internal classifier have been performed by Particle Image Velocimetry (PIV) and by numerical predictions of the fluid flow in the complete mill using a commercial CFD solver. Different pin geometries have been studied at various peripheral velocities of the grinding disk and the classifier. The classifier velocity does not influence the velocity profiles near the impact elements in the main flow direction and vice versa, the flow in the grinding zone has little influence on the classification. The velocity profile in front of the impact element, where the comminution process takes place, is constant with time and preserves a characteristic form independent of the operational conditions.     

Waterborne polyurethane wood coatings based on rapeseed fatty acid methyl esters

Trends in wood coatings are driven to waterborne systems and to renewable resources. Vegetable oils are well known for wood coatings, e.g. alkyds or polyurethane dispersions. In this context, fatty acid methyl esters turn out to be an alternative to technical fatty acids and vegetable oils. High contents of hydrophobic oil-based monomers require a sufficient understanding of the dispersion stability. This study shows the influence of hydrophobic monomers, ionic centers, degree of neutralization, and stirring procedure to the particle size distribution and dispersion stability. Furthermore, the impact of these parameters on the resulting coating film properties was investigated.     

Probing mesopore connectivity in hierarchical nanoporous materials

Assessing connectivity of mesopores formed in microporous matrices is of importance for a wide range of applications. In this work we present an experimental study of the transport of n-hexane and nitrobenzene in a commercial activated carbon material containing purposefully introduced mesoporosity. The experimental results on diffusivities and activation energies for diffusion, as obtained using the pulsed field gradient technique of NMR, corroborate the information on pore architecture as resulting from adsorption isotherm measurement and unequivocally demonstrate the material-spanning continuity of the formed mesopore network, as a prerequisite for an unlimited transport enhancement in comparison with the purely microporous equivalent.     

Growth of carbon nanotube forests between a bi-metallic catalyst layer and a SiO2 substrate to form a self-assembled carbon–metal heterostructure

A special nanostructure was formed by the growth of carbon nanotubes (CNTs) between a substrate and a thin bi-metallic catalyst layer using a thermal chemical vapor deposition process. The catalyst layer is composed of adjacently disposed Cr and Ni phases formed prior to CNT growth. The Cr/Ni layer serves as a bi-metallic catalyst layer, which is pushed away from the substrate as a thin and continuous nanomembrane with the growth of CNTs. The self-assembled CNT–catalyst heterostructure possesses a smooth surface (RMS = 2.9 nm) with a metallic shine. Directly interlinked to the Cr/Ni layer, dense and vertically aligned multi-walled CNTs are found. Compared to conventional CNT films, the structure has significant advantages for CNT integration. From technology point of view, the structure allows further processing without impact on the CNTs as well as transfer of pristine vertically aligned CNTs to arbitrary substrates. Moreover, the as-grown CNT films provide an interface ideal for further electrical, thermal and mechanical contacting of CNT films. We present structural investigations of this special CNT–metal heterostructure. Furthermore, we discuss possible interface mechanisms during catalyst layer formation and CNT growth.     

Catalytic steam reforming of model biogas

Catalytic steam reforming of a model biogas (CH₄/CO₂ = 60/40) is investigated to produce H₂-rich synthesis gas. Gas engines benefit from synthesis gas fuel in terms of higher efficiency and lower NO_x production when compared to raw biogas or CH₄. The process is realized in a fixed bed reactor with a Ni-based catalyst on CaO/Al₂O₃ support. To optimize the performance, the reactor temperature and the amount of excess steam are varied. The experimental results are compared to the theoretical values from thermodynamic calculation and the main trends of CH₄ conversion and H₂ yield are analyzed and verified. Finally, optimal reactor temperature is pointed out and a range of potential steam to methane ratios is presented. The experimental results will be applied to design a steam reformer at an existing anaerobic biomass fermentation plant in Strem, Austria.