Mechanism of formation of urchin-like ZnO

Thin films composed of ZnO nanowires (NWs) hierarchically organized with an urchin-like 3D morphology were obtained by combining the electrochemical deposition and sphere lithography methods. Deposited on a transparent conductive oxide substrate (TCO), a monolayer of carboxylate modified polystyrene spheres organized with a hexagonal closed-packed structure played the role of a template. The spheres were activated in a solution of zinc chloride by the formation of bonds between the carboxylate terminals and the Zn²⁺ ions and were used as a template for the electrodeposition of vertically aligned ZnO NWs around them. Without this treatment, ZnO NWs were deposited only on the TCO substrate between the PS spheres. To reach a density of nanowires high enough to obtain the urchin morphology, the concentration of ZnCl₂ had to be at least equal to 2 M. It was also found, as soon as small grains of ZnO started to be electrodeposited on the polystyrene spheres that the spheres were no longer close packed. The space created between them increased with the increase in the number of small ZnO grains and the increase in their length, allowing the further growth of the nanowires between the spheres. As a result the initial round shape of the spheres was modified and the urchin-like ZnO exhibited an ellipsoidal shape.     

Failure mechanism of thin Al2O3 coatings grown by atomic layer deposition for corrosion protection of carbon steel

Combined analysis by electrochemical impedance spectroscopy (EIS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and field emission scanning electron microscopy (FESEM) of the corrosion protection provided to carbon steel by thin (50 nm) Al₂O₃ coatings grown by atomic layer deposition (ALD) and its failure mechanism is reported. In spite of excellent sealing properties, the results show an average dissolution rate of the alumina coating of ∼7 nm h⁻¹ in neutral 0.2 M NaCl and increasing porosity of the remaining layers with increasing immersion time. Alumina dissolution is triggered by the penetration of the solution via cracks/pinholes through the coating to the substrate surface where oxygen reduction takes place, raising the pH. At defective substrate surface sites of high aspect ratio and concentrated residual mechanical stress (along scratches) presumably exposing a higher steel surface fraction, localized dissolution of the coating is promoted by a more facile access of the solution to the substrate surface enhancing oxygen reduction. De-adhesion of the coating is also promoted in these sites by the ingress of the anodic dissolution trenching the steel surface. Localized corrosion of the alloy (i.e. pitting) is triggered prior to complete dissolution of the alumina film on the elsewhere still coated surface matrix.     

Mechanism of anodic oxidation of molybdenum in nearly-neutral electrolytes studied by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy

Anodic oxidation of molybdenum in weakly acidic, nearly neutral and weakly alkaline electrolytes was studied by voltammetric and electrochemical impedance spectroscopic measurements in a wide potential and pH range. Current vs. potential curves were found to exhibit two pseudo-Tafel regions suggesting two parallel pathways of the dissolution process. Electrochemical impedance spectra indicated the presence of at least two reaction intermediates. X-ray photoelectron spectroscopic (XPS) results pointed to the formation of an oxide containing Mo(IV), Mo(V) and Mo(VI), the exact ratio between different valence states depending on potential and pH of the solution. A physico-chemical model of the processes is proposed and a set of kinetic equations for the steady-state current vs. potential curve and the impedance response are derived. The model is found to reproduce quantitatively the current vs. potential curves and impedance spectra at a range of potentials and pH and to agree qualitatively with the XPS results. Subject to further improvement, the model could serve as a starting point for the optimization of the electrochemical fabrication of functional molybdenum oxide coatings.     

Gas sensors based on thick films of semi-conducting single walled carbon nanotubes

A comparative study was made of sorted semi-conducting single walled carbon nanotube (SWCNT) films and unsorted SWCNT films for gas sensing applications. The transmission line method is used to monitor separately the SWCNTs film resistance and the contact resistance between electrodes and the SWCNTs, thus revealing that the sensing mechanism mainly relies on a modification of the tube conductivity during gas exposure. The fabricated sensors demonstrate a detection limit of 20 ppb NO₂ and 600 ppb NH₃ mainly attributed to experimental setup limitations. Moreover, semi-conducting nanotubes happened to be 2.5 times more sensitive to NH₃ than unsorted ones, thus proving that selectivity can be improved by sorting the SWCNTs. The temperature dependence of the sensor sensitivity was studied, and a good agreement was found between experimental results and the Langmuir adsorption model.     

Dye–fiber interactions in PET fibers: Hydrogen bonding studied by IR‐spectroscopy

Dye–fiber interactions are studied in poly (ethylene terephthalate) fibers by FT‐IR spectroscopy. It is shown for the first time that DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy) serves as an easy applicable and accurate technique for the study of fibrous structures. This article focuses on the possible hydrogen bond interactions in the dye–fiber system, where the PET fibers are dyed with anthraquinone‐based disperse dyes. The dyes and related anthraquinone structures are studied in both the dilute solution state, the solid state, and as present in the PET fibers. It is proven that 1‐amino anthraquinones show strong “chelate‐type” intramolecular hydrogen bonding in all three states. In the fibers an important supplementary intermolecular hydrogen bonding with the C?O groups in the PET fiber is observed. The extend of hydrogen bonding seems to be prone to dye concentration variations. Further analysis by modulated differential scanning calorimetry links the hydrogen bonding to an intrinsic plasticizing effect of the dyes affecting the dye diffusion process. This thus offers a tool for the fundamental understanding of the dyeing process and possible observed differences in dyeing behavior in dye–fiber systems. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Multiphase coatings from complex radiation curable polyurethane dispersions

The waterborne nature of radiation curable polyurethane dispersions largely respond to the current environmental concerns and do not require any additional coalescent since the film formation (drying) and hardening (photo-curing) take place in distinct steps. It is possible to design aqueous dispersions with distinct polymer particle populations resulting in micro-structured coatings with optimized properties over a wide range of curing conditions. Mixed dispersions based on hard and soft acrylated polyurethane particles were used as model systems for the present study. The minimum film formation temperature has been investigated as a function of the hard:soft polymer ratio. The elastic modulus of the dry coatings shows a reinforcing effect consistent with the inclusion of hard domains in a soft continuous matrix. However, the level of reinforcement is not properly predicted by the usual mechanical models and it is qualitatively accounted for by assuming a composition gradient (interphase) between the hard domains and the matrix. The multiple-phase structure was clearly established by Atomic Force Microscopy in agreement with thermal analysis data. Furthermore the local nanoscale mechanical properties were mapped using a new imaging mode based on real-time force–distance curve analysis. Finally, the coatings prepared using this multiple-phase pattern present a clear benefit over conventional homogeneous coatings by offering an improved balance of chemical and mechanical resistance in pigmented systems applied on melamine-coated MDF panels.     

An FTIR/ATR in situ study of sorption and transport in corrosion protective organic coatings: Paper 2. The effects of temperature and isotopic dilution

A detailed temperature variation (18–50 °C) FTIR/ATR study of sorption and desorption of water into a series of cured epoxy resins has been reported. For higher temperatures (35–50 °C) the data were modelled with a single Fickian diffusion equation, giving an increased D as the temperature increased and an activation energy (E_A) in the 55–60 kJ mol⁻¹ region. At lower temperatures (18–35 °C)—well-below the T_g—a two-stage sorption equation was needed and the apparent E_A was negative. This is probably associated with changes in water clustering among the distributed ‘voids’ in the glassy polymer associated with chain relaxation at extended times. The use of D₂O as a penetrant allowed diffusion coefficient measurements for highly dense epoxy matrices, where FTIR/ATR cannot detect the ν(OH) band of water over and above the residual polymer–OH groups (in the dry state). The data for the D₂O studies were notably influenced by isotopic exchange; which was found to be a diffusion controlled process, even in a polymer matrix.     

Recycling zinc oxide varistor blocks for electro‐active silicone composites

The recycling process toward the elimination of varistor wastes into new electro‐active silicon composites has been investigated. We studied the dependence of the E‐J characteristics on the aggregate content in the polymer matrix. Formulations with 40 vol.% metal oxide varistor aggregates in the 100‐200 μm range exhibit reliable nonlinear behavior with a switching voltage of 280±30 V/mm. The breakdown voltage of the composite decreases as both filler's diameter and filler's volume fraction increases in the 550‐220 V/mm and 440‐280 V/mm range, respectively. This paves the way for the valorization of varistors based zinc oxide (ZnO) ceramics.     

Structure and analgesic properties of layered double hydroxides intercalated with low amounts of ibuprofen

Ibuprofen‐intercalated layered double hydroxides (LDH‐IBU) have been successfully synthesized via a coprecipitation method with a nominal [Al³⁺]/[Mg²⁺] ratio of 0.5 and a variable molar IBU/([Al³⁺]+[Mg²⁺]) ratio of 0, 0.15, 0.18, 0.24, 0.36, and 0.72. After an accurate determination of the composition, the nature of the intercalated species and the effective intercalation yield from to IBU, it is shown that the synthesis route used allows a good control of the quantity of intercalated IBU within the LDH framework. This results in different samples with full or partial IBU intercalation in the interlayer space in exchange of nitrate anions. The analysis of the X‐ray diffraction basal reflections reveals that the intercalation of IBU in the framework only increases the basal distances with no alteration of the brucite‐type layers. Also, a computational study used to model the positions and shapes of the basal reflections showed that the structure of the nonfully intercalated compounds follows a random interstratification scheme. Finally, three samples ranging from slightly to fully IBU‐intercalated galleries were selected for preliminary in vivo assays. These tests showed a strong tendency that after 24 hours the low yield of IBU‐intercalated compounds are almost as efficient as the fully intercalated sample.     

SIMULTANEOUS GC/MS ANALYSIS OF POLYCYCLIC AROMATIC HYDROCARBONS AND THEIR NITRATED DERIVATIVES IN ATMOSPHERIC PARTICULATE MATTER FROM WORKPLACES

Abstract

PAH are routinely analyzed using HPLC/FD. This technique is unsuitable for analyzing NPAH. This study aims at developing a reliable method, using GC/MS, and applying this technique to actual samples from small volumes of atmospheric particulate matter from workplaces. Mixtures of PAH and NPAH were separated by GC/MS and detected by electronic impact (EI) or negative ion chemical ionization (NICI). Analyses on twelve actual samples were thus carried out by sampling a small volume of atmosphere (≈0.5 m ³ ) from five different industrial workplaces. Samples displayed wide differences from one industrial workplace to another, and this can be explained by the specific methods applied. The PAH and NPAH concentrations also varied with time in the same industrial workplace. NPAH concentrations were not correlated with PAH concentrations, underscoring the complex chemical mechanisms involved in NPAH formation. PAH and NPAH formation appeared to be dependent on both industrial activities and uncontrolled physicochemical conditions.