Stability of rare‐earth‐doped spherical yttria‐stabilized zirconia synthesized by ultrasonic spray pyrolysis

Phase stability is one of the crucial requirements for any material that can be used at elevated temperature applications such as thermal barrier coating (TBC). The most traditional TBC material, partially stabilized zirconia, limits the operating temperature due to its phase transformation. Conversely, the low thermal conductivity of fully stabilized zirconia (YSZ) may enable effective reduction in the surface temperature on the coated component, while avoiding deleterious phase transitions, although still being subjected to sintering and grain growth. It has been reported that addition of rare‐earths as dopants to YSZ can significantly increase resistance to grain growth at high temperature. Keeping this under consideration, this work investigates the role of rare‐earths (lanthanum and gadolinium) in increasing thermal stability of YSZ microspheres, the building blocks for high‐temperature photonics for reflective TBC. The spheres were produced by ultrasonic spray pyrolysis, and the doping led to significant improvement of stability by significant inhibition of grain growth. While the individual dopants showed significant growth and sintering inhibition up to 900°C, co‐doping with 4% (in mol) of each (Gd and La) led to coarsening resistance up to 1000°C for 3 hours, when particles retained reasonable spherical features with nanometric crystallite sizes.     

ASGPR‐Mediated Uptake of Multivalent Glycoconjugates for Drug Delivery in Hepatocytes

Liver cells are an essential target for drug delivery in many diseases. The hepatocytes express the asialoglycoprotein receptor (ASGPR), which promotes specific uptake by means of N‐acetylgalactosamine (GalNAc) recognition. In this work, we designed two different chemical architectures to treat Wilson's disease by intracellular copper chelation. Two glycoconjugates functionalized with three or four GalNAc units each were shown to enter hepatic cells and chelate copper. Here, we studied two series of compounds derived from these glycoconjugates to find key parameters for the targeting of human hepatocytes. Efficient cellular uptake was demonstrated by flow cytometry using HepG2 human heptic cells that express the human oligomeric ASGPR. Dissociation constants in the nanomolar range showed efficient multivalent interactions with the receptor. Both architectures were therefore concluded to be able to compete with endogeneous asialoglycoproteins and serve as good vehicles for drug delivery in hepatocytes.     

Nuclear Magnetic Resonance Investigation of the Effect of pH on Micelle Formation by the Amino Acid‐Based Surfactant Undecyl l‐Phenylalaninate

Micelle formation by the anionic amino acid‐based surfactant undecyl l ‐phenylalaninate (und‐Phe) was investigated as a function of pH in solutions containing either Na⁺, l ‐arginine, l ‐lysine, or l ‐ornithine counterions. In each mixture, the surfactant's critical micelle concentration (CMC) was the lowest at low pH and increased as solutions became more basic. Below pH 9, surfactant solutions containing l ‐arginine and l ‐lysine had lower CMC than the corresponding solutions with Na⁺ counterions. Nuclear magnetic resonance (NMR) diffusometry and dynamic light scattering studies revealed that und‐Phe micelles with Na⁺ counterions had hydrodynamic radii of approximately 15 Å throughout the investigated pH range. Furthermore, l ‐arginine, l ‐lysine, and l ‐ornithine were found to bind most strongly to the micelles below pH 9 when the counterions were cationic. Above pH 9, the counterions became zwitterionic and dissociated from the micelle surface. In und‐Phe/l ‐arginine solution, counterion dissociation was accompanied by a decrease in the hydrodynamic radius of the micelle. However, in experiments with l ‐lysine and l ‐ornithine, micelle radii remained the same at low pH when counterions were bound and at high pH when they were not. This result suggested that l ‐arginine is attached perpendicular to the micelle surface through its guanidinium functional group with the remainder of the molecule extending into solution. Contrastingly, l ‐lysine and l ‐ornithine likely bind parallel to the micelle surface with their two amine functional groups interacting with different surfactant monomers. This model was consistent with the results from two‐dimensional ROESY (rotating frame Overhauser enhancement spectroscopy) NMR experiments. Two‐dimensional NMR also showed that in und‐Phe micelles, the aromatic rings on the phenylalanine headgroups were rotated toward the hydrocarbon core of micelle.     

Characterisation of electrodeposited nanocrystalline Ni–Mo alloys

Ni–Mo nanocrystalline layers were electrodeposited using direct current from citrate–ammonia solutions. The quartz crystal microbalance investigation confirms that the discharge process starts with hydrogen evolution before the onset of the alloy deposition. The grain size was estimated from X-ray line broadening. It decreases when the molybdenum content is increased. It is smaller for layers deposited at pH 9.5 than 8.5. The microhardness exhibits a maximum close to 800 Vickers for _Mo around 17 wt%. For higher _Mo a softening is observed showing a deviation from Hall-Petch behaviour due to small grain size. In deaerated hydrochloric solutions, the layers show a large passivation domain without any pitting. The corrosion currents as well as the passivation currents, higher than for the bulk Hastelloy B alloy, decrease when _Mo is increased.     

Dissolution of softwood kraft pulps by direct derivatization in lithium chloride/N,N‐dimethylacetamide

A method for the characterization of the molar mass distributions (MMDs) of softwood kraft pulps dissolved in 0.5% lithium chloride (LiCl)/N,N‐dimethylacetamide (DMAc) by size exclusion chromatography is presented. The method is based on derivatization with ethyl isocyanate and the dissolution of samples in 8% LiCl/DMAc. In this study, the derivatization of hardwood kraft pulps did not influence the MMD. In the case of softwood pulps, however, the derivatization decreased the proportion of the high‐molecular‐mass material and increased the proportion of the low‐molecular‐mass material, which resulted in a distribution similar to the MMD of a hardwood kraft pulp. The results suggest that associations between hemicellulose and cellulose in the softwood kraft pulp were ruptured during derivatization. This led to a more correct estimation of the MMD of derivatized softwood kraft pulps than obtained by the dissolution of nonderivatized samples. This new method offers several advantages over derivatization with phenyl isocyanate: a precipitation step is not necessary, it is possible to follow the lignin distribution in the samples, and the method allows very high levels of dissolution of softwood kraft pulps up to a κ number of around 50. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 424–431, 2004     

Numerical,wind-tunnel,and atmospheric evaluation of a turbulent ground-based inlet sampling system

The use of inlets for transferring aerosols from the environment to instrumentation can introduce uncertainty in the measurement of aerosol properties. Aerosol loss during this process is a non-negligible issue that may bias the subsequent measurements. These loss mechanisms include aspiration at the inlet head and deposition/evaporation/condensation during transport through the sampling lines. Coarse-mode aerosol is significantly impacted by the aspiration and inertial loss mechanisms within an inlet system. This work uses wind tunnel experiments to investigate aerosol losses through the Storm Peak Laboratory’s (SPL) new aerosol inlet system. The inlet is used extensively for both intensive field campaigns and long-term aerosol monitoring. The results of numerical simulations of the SPL aerosol inlet sampling efficiency are provided at several wind speeds, and experimental results demonstrate the system has a 50% cut off for the coarse-mode at an aerodynamic diameter of approximately 13?μm and wind speed of 0.5?m s^?1. This investigation will lead to improved accuracy of in situ aerosol measurements at SPL and this system can be replicated at other atmospheric stations.

Copyright © 2019 American Association for Aerosol Research     

Deformation behaviour of an advanced nickel-based superalloy studied by neutron diffraction and electron microscopy

Deformation mechanisms under tensile loading at room temperature have been studied in a polycrystalline nickel-based superalloy containing close to 50 vol.% γ′. In order to identify the effect of γ′ particle size on deformation mechanisms, model microstructures with unimodal γ′ size distributions were developed. The investigations were carried out by combining in situ loading experiments using neutron diffraction and two-site elasto-plastic self-consistent plasticity modelling with detailed post-mortem electron microscopy. The microscopy work also includes results for samples strained at 500 °C. During early plastic deformation, the diffraction data demonstrate that γ and γ′ display the same elastic strain response, indicating that at this stage γ′ is cut by dislocations regardless of the γ′ particle size. Scanning electron microscopy studies showed an abundance of shearing processes in all three microstructures, hence supporting the conclusions drawn from the diffraction experiment. As the material is further deformed, elastic load transfer from γ to γ′ was observed in the medium (130 nm) and coarse (230 nm) γ′ microstructures but not in the fine (90 nm) γ′ microstructure. The load transfer can be explained by assuming that Orowan looping becomes an additional operative deformation mode. Transmission electron microscopy confirmed that in the fine γ′ microstructure deformation takes place by strongly coupled dislocations cutting the γ′, while the medium and coarse γ′ microstructures showed additional signs of Orowan looping.     

TPA‐PPEs – New alternating donor copolymers for potential application in photovoltaic devices

A series of phenyleneethynylene copolymers with triphenylamine units as hole‐transporting moieties (TPA‐PPEs) were synthesized by the palladium‐catalyzed cross‐coupling polycondensation of diethynyltriphenylamines and selected dihalogen comonomers, for instance substituted benzene, thiophene, benzothiadiazole, or anthracene. Incorporation of the electron‐rich amino group into the PPE backbone does not interrupt the main chain conjugation. Furthermore, it has a decreasing effect on the oxidation potential, thus makes these polymers interesting as hole‐injection/hole‐transporting materials. The chemical structure of the new alternating copolymers was confirmed by ¹H and ¹³C NMR spectroscopy and elemental analysis and gel‐permeation chromatography (GPC; THF, M_n ≈ 15,000–30,000 g/mol) was conducted. Furthermore, their optical properties were investigated by UV/vis spectroscopy. The TPA‐PPEs exhibit absorption maxima at around 400 nm (π‐π*), except anthracene containing copolymer 3f (λ_max = 514 nm in THF) and benzothiadiazole containing one 3g (λ_max = 503 nm in THF). The TPA copolymers have oxidation potentials about 1.1 V (Ag/AgCl). They are good photoconducting materials ( 3a : I_Photo = 4 × 10^?10 A at 425 nm (400 V), 3g : I_Photo = 1.3 × 10^?11 A at λ_max = 500 nm (20 V)) and show emission after excitation at around 450 nm (560 nm 3f ). Their application in nonoptimized polymer solar cells (bulk heterojunction) led to power conversion efficiencies of around 1–1.8% after illumination with 100 mW/cm² of AM1.5. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009