Energy filtered transmission electron microscopy for the physico-chemical characterization of aquatic submicron colloids

A combination of energy filtered transmission electron microscopic (EF-TEM) procedures is proposed for the non-perturbing physico-chemical characterization of submicron mineral and organic colloids in aquatic systems. Synthetic hematite microparticles and xanthan polysaccharides were used as well-characterized model colloids in order to determine the optimum EF-TEM analysis conditions. In this paper, it is demonstrated that (i) our model colloids are morphologically representative of naturally occurring mineral/organic associations, (ii) EF-TEM allows the detection of fine xanthan ultrastructures without artefacts of conventional staining methods and (iii) submicron hematite particles can be specifically visualized and spectrometrically measured by EF-TEM within a hematite/xanthan mixture. This EF-TEM procedure appears to be appropriate for the characterization of real aquatic samples.     

Coherence during scattering of fast H atoms from a LiF(001) surface

The coherence for diffraction effects during grazing scattering of fast hydrogen and helium atoms from a LiF(001) surface with energies up to some keV is investigated via the coincident detection of two-dimensional angular distributions for scattered projectiles with their energy loss. For keV H atoms, we identify electronic excitations of the target surface as the dominant mechanism for decoherence, whereas for He atoms this contribution is small. The suppression of electronic excitations owing to the band gap of insulators plays an essential role for preserving quantum coherence and thus for the application of fast atom diffraction as a surface analytical tool.     

Self-assembly of class II hydrophobins on polar surfaces

Hydrophobins are structural proteins produced by filamentous fungi that are amphiphilic and function through self-assembling into structures such as membranes. They have diverse roles in the growth and development of fungi, for example in adhesion to substrates, for reducing surface tension to allow aerial growth, in forming protective coatings on spores and other structures. Hydrophobin membranes at the air-water interface and on hydrophobic solids are well studied, but understanding how hydrophobins can bind to a polar surface to make it more hydrophobic has remained unresolved. Here we have studied different class II hydrophobins for their ability to bind to polar surfaces that were immersed in buffer solution. We show here that the binding under some conditions results in a significant increase of water contact angle (WCA) on some surfaces. The highest contact angles were obtained on cationic surfaces where the hydrophobin HFBI has an average WCA of 62.6° at pH 9.0, HFBII an average of 69.0° at pH 8.0, and HFBIII had an average WCA of 61.9° at pH 8.0. The binding of the hydrophobins to the positively charged surface was shown to depend on both pH and ionic strength. The results are significant for understanding the mechanism for formation of structures such as the surface of mycelia or fungal spore coatings as well as for possible technical applications.     

Following the evolution of morphology, composition and crystallography of alumina based catalysts after laser ablation: Implications for analysis by LA-ICP-AES

Fundamental understanding of aerosol formation during laser ablation is important for the development of LA-ICP analysis of complex samples. Using a Lina Spark Atomizer™, the application of this technique to the field of heterogeneous catalysis gave an accuracy of 5–15% while extreme values of +100% could be obtained in some cases. To improve understanding of laser ablation processes, particles generated during ablation of alumina based catalysts were collected and analysed using different microscopy and surface analysis techniques. Morphological study by scanning electron microscopy showed that most of the particles leaving the ablation cell were nanoparticle aggregates generated from vapor condensation. An XRD study of these aerosols revealed that the condensation converge on the formation of a spinel structure with large coherence domains. Elemental composition of the aerosol was also followed and exhibited differences between a catalyst containing large Mo concentration or low Pt concentration.     

A study on the aerodynamic instability of attenuating liquid sheets

We describe the characteristics of a radially spreading unstable liquid sheet in quiescent air via optical measurement techniques and linear instability theory. A high speed CCD camera system and a complimentary laser refraction method were employed to measure the intact sheet diameter, unstable wave lengths, wave speed, wave frequency spectrum and spatial wave growth rates. Linear instability models for thinning, viscous and inviscid liquid sheets, which are available from the literature, allow for a comparison of experimental data and predicted sheet behaviour. The last section evaluates the differences and similarities between the current liquid sheet experiment and industrial spray applications such as fuel atomisation via pressure-swirl nozzles.     

Silicon speciation by gas chromatography coupled to mass spectrometry in gasolines

A method for the speciation of silicon compounds in petroleum products was developed using gas chromatography coupled to mass spectrometry (GC-MS). Prior to analysis, several precautions about storage and conservation were applied for all samples. In spiked gasoline samples, limits of detection between 24 and 69 μg kg(-1) for cyclic siloxanes (D(4)-D(6)) and between 1 and 7 μg kg(-1) for other species were obtained. In this study, cyclic siloxanes (D(n)) and one ethoxysilane were quantified for the first time in petroleum products by a specific method based on response factor calculation to an internal standard. This method was applied to four samples of naphthas and gasolines obtained from a steam cracking process. Cyclic siloxanes were predominant in four investigated samples with concentrations ranging between 101 and 2204 μg kg(-1). Cyclic siloxane content decreased with an increase in their degree of polymerization. During a steam cracking process, silicon concentrations determined by GC-MS SIM (single ion monitoring) significantly increase. This trend was confirmed by ICP-OES (inductively coupled plasma optical emission spectroscopy) measurements but a difference on the total silicon content was observed, certainly highlighting the presence of unknown silicon species. GC-MS SIM method gives access to the chemical nature of the silicon species, which is crucial for the understanding of hydrotreatment catalyst poisoning in the oil and gas industry.     

Cell‐Mediated Proteolytic Release of Growth Factors from Poly(Ethylene Glycol) Matrices

Engineering in vitro tissue mimetics that resemble the corresponding living tissues requires the 3D arrangement of tissue progenitor cells and their differentiation by localized growth factor (GF) signaling cues. Recent technological advances open a large field of possibilities for the creation of complex GF arrangements. Additionally, cell‐instructive biomaterials, which bind GFs by various mechanisms and release them with different kinetics depending on binding affinity, have become available. This paper describes the development of a matrix metalloproteinase (MMP)‐degradable streptavidin‐based linker module, which allows the release of immobilized GFs from synthetic biomimetic poly(ethylene glycol) hydrogels independently of the hydrogel degradation. The MMP‐sensitive streptavidin linker is shown to efficiently bind biotinylated molecules, and as proof of concept, bone morphogenetic protein‐2 (BMP‐2) delivery via the MMP‐degradable linker is used to induce osteogenic differentiation in C2C12 cells and mesenchymal stem cells. The results show a significantly increased net effect of proteolytically releasable BMP‐2 in comparison to stably immobilized and soluble BMP‐2. This study indicates that a GF delivery system directly responsive to cellular activity can have important implications for the synthesis of tissue mimetics and regenerative medicine, as it can influence the availability, the localization of effects, as well as efficacy of employed GFs.

     

X-ray fluorescence spectrometry for high throughput analysis of atmospheric aerosol samples: The benefits of synchrotron X-rays

The determination of trace element mass concentrations in ambient air with a time resolution higher than one day represents an urgent need in atmospheric research. It involves the application of a specific technique both for the aerosol sampling and the subsequent analysis of the collected particles. Beside the intrinsic sensitivity of the analytical method, the sampling interval and thus the quantity of collected material that is available for subsequent analysis is a major factor driving the overall trace element detection power. This is demonstrated for synchrotron radiation X-ray fluorescence spectrometry (SR-XRF) of aerosol samples collected with a rotating drum impactor (RDI) in hourly intervals and three particle size ranges. The total aerosol mass on the 1-h samples is in the range of 10 µg. An experimental detection of the nanogram amounts of trace elements with the help of synchrotron X-rays was only achievable by the design of a fit-for-purpose sample holder system, which considered the boundary conditions both from particle sampling and analysis. A 6-µm polypropylene substrate film has evolved as substrate of choice, due to its practical applicability during sampling and its suitable spectroscopic behavior. In contrast to monochromatic excitation conditions, the application of a ‘white’ beam led to a better spectral signal-to-background ratio. Despite the low sample mass, a counting time of less than 30 s per 1-h aerosol sample led to sufficient counting statistics. Therefore the RDI-SR-XRF method represents a high-throughput analysis procedure without the need for any sample preparation. The analysis of a multielemental mass standard film by SR-XRF, laboratory-based wavelength-dispersive XRF spectrometry and laboratory-based micro XRF spectrometry showed that the laboratory-based methods were no alternatives to the SR-XRF method with respect to sensitivity and efficiency of analysis.     

Sensitivity improvement in ICP MS analysis of fuels and light petroleum matrices using a microflow nebulizer and heated spray chamber sample introduction

Reasons for signal suppression during the analysis of light petroleum matrices by inductively coupled plasma mass spectrometry (ICP MS) were examined. A decrease of the ionization efficiency of the plasma was found to be the principal factor responsible for this loss of sensitivity. Consequently, an interface based on a total consumption micronebulizer and a heated spray chamber was constructed to alleviate this problem. A method based on flow-injection ICP MS using this interface was developed for the direct multielement analysis of undiluted fuels (gasoline, kerosene) and gas condensates offering an increase in sensitivity by at least a factor of 3-4 in comparison with the existing setups.     

Surface termination of the NdGaO3(1 1 0)

Auger electron spectroscopy using excitation via grazing impact of protons was applied to determine the elemental composition of the topmost and near-surface layers of a NdGaO₃(1 1 0) substrate. The preparation conditions of vicinal NdGaO₃ substrates were optimized by varying the annealing temperature, time, and gas atmosphere. Well prepared surfaces show regularly arranged, atomically smooth terraces with single-atomic steps. The surfaces were always NdO terminated with a small amount of Ga (2-4%) atoms on the surface. A Ga and O depletion layer with a thickness of about 4 nm has been detected at optimized preparation conditions.