Correlation between superhydrophobicity and the power spectral density of randomly rough surfaces

We show experimentally and analytically that for single-valued, isotropic, homogeneous, randomly rough surfaces consisting of bumps randomly protruding over a continuous background, superhydrophobicity is related to the power spectral density of the surface height, which can be derived from microscopy measurements. More precisely, superhydrophobicity correlates with the third moment of the power spectral density, which is directly related to the notion of Wenzel roughness (i.e., the ratio between the real area of the surface and its projected area). In addition, we explain why randomly rough surfaces with identical root-mean-square roughness values may behave differently with respect to water repellence and why roughness components with wavelength larger than 10 μm are not likely to be of importance or, stated otherwise, why superhydrophobicity often requires a contribution from submicrometer-scale components such as nanoparticles. The analysis developed here also shows that the simple thermodynamic arguments relating superhydrophobicity to an increase in the sample area are valid for this type of surface, and we hope that it will help researchers to fabricate efficient superhydrophobic surfaces based on the rational design of their power spectral density.     

Impact of pinning of the triple contact line on electrowetting performance

Pinning of the triple contact line adversely affects electrowetting on dielectric. Electrowetting response of substrates with contact angle hysteresis ranging from 1° to 30° has been characterized, and the results are interpreted within the framework of electromechanics corrected for pinning. The relationship between contact angle hysteresis, threshold potential for liquid actuation, and electrowetting hysteresis is quantified. Our results demonstrate that a modified electrowetting equation, based on balance of forces (including the pinning forces) acting on the triple contact line and on the drop, describes the electrowetting response of substrates with significant contact angle hysteresis. Finally, the surface properties of PDMS Sylgard 184 were found to be influenced by the electric field.     

Intraspecific variation in the essential oils from Drimys brasiliensis leaves and stem barks

The essential oils from leaves and stem barks of Drimys brasiliensis Miers (Winteraceae), collected in July and December 2008, were analyzed by GC/FID and GC/MS. The stem bark oils were composed mainly of monoterpenes (July, 45 +/- 3%; December, 92 +/- 4%), while the oils from leaves showed the predominance of sesquiterpenes (July, 47 +/- 1%; December, 55 +/- 1%). The variation in the relative amount of constituents could be associated, at least in part, to several microclimatic parameters such as precipitation, temperature and/or phenological state, which were different for each collection of D. brasiliensis.     

Oxovanadium complexes in catalytic oxidations

This contribution is an overview on recent advances (since 2000) on the application of oxovanadium complexes as catalysts or mediators for oxidations by molecular oxygen, peroxidative oxygenations (both including epoxidations), halogenations and carboxylations of aliphatic and aromatic hydrocarbons, and/or olefins, toward the syntheses of a variety of organic compounds, such as alcohols, ketones, epoxides, aldehydes, organohalides and orcarboxylic acids. Some of these systems operate in liquid media, whereas others involve VO-catalysts immobilized on solid supports.     

Pressure swing adsorption for CO<Subscript>2</Subscript> capture in Fischer-Tropsch fuels production from biomass

Environmental concerns and oil price rises and dependency promoted strong research in alternative fuel sources and vectors. Fischer-Tropsch products are considered a valid alternative to oil derivatives having the advantage of being able to share current infrastructures. As a renewable source of energy, synthesis gas obtained from biomass gasification presents itself as a sustainable alternative. However, prior to hydrocarbon conversion, the bio-syngas must be conditioned, which includes the removal of carbon dioxide for subsequent sequestration and capture. A pressure swing adsorption cycle was developed for the removal and concentration of CO₂ from the bio-syngas stream. Activated carbon was chosen as adsorbent. The simulation results showed that it was possible to produce a (H₂ + CO) product with a H₂/CO stoichiometric ratio of 2.14 (suitable as feed stream for the Fischer-Tropsch reactor) and a CO₂ product with a purity of 95.18%. A CO₂ recovery of 90.3% was obtained. A power consumption of 3.36 MW was achieved, which represents a reduction of about 28% when compared to a Rectisol process with the same recovery.     

Differential scanning calorimetry study of the solidification sequence of austenitic stainless steel

The solidification sequence of austenitic stainless steels can be predicted with thermodynamic calculations. Another way is to use models where the value of the Cr_eq./Ni_eq. ratio determines the relationship between the solidification mode and the composition factor. In this study the solidification of AISI 304LN stainless steel at different cooling rates was studied using differential scanning calorimetry (DSC). The samples were linearly heated above the liquidus temperature to 1550 °C at heating rates of 5, 10, and 25 K/min. The solidification (cooling) scans from 1550 °C involved the same selected ramps. After the DSC measurements the samples were metallographically analyzed to reveal the variations in the solidification microstructures. The microhardness of the solidified samples was also measured. It was found that the cooling rate critically influenced the solidification. The solidification behavior, which depends on the cooling rate, determines the evolution of the microstructure. At the slowest cooling rates a relief-cell morphology was observed, and at the fastest cooling rate the formation of dendrites was evident. With an increasing cooling rate the liquidus temperature decreased and the reaction enthalpy increased.     

A simple and green analytical method for determination of glyphosate in commercial formulations and water by diffuse reflectance spectroscopy

This article describes a simple, inexpensive, and environmentally friendly method for the monitoring of glyphosate using diffuse reflectance spectroscopy. The proposed method is based on reflectance measurements of the colored compound produced from the spot test reaction between glyphosate and p-dimethylaminocinnamaldehyde (p-DAC) in acid medium, using a filter paper as solid support. Experimental designs were used to optimize the analytical conditions. All reflectance measurements were carried out at 495 nm. Under optimal conditions, the glyphosate calibration graphs obtained by plotting the optical density of the reflectance signal (AR) against the concentration were linear in the range 50-500 μg mL(-1), with a correlation coefficient of 0.9987. The limit of detection (LOD) for glyphosate was 7.28 μg mL(-1). The technique was successfully applied to the direct determination of glyphosate in commercial formulations, as well as in water samples (river water, pure water and mineral drinking water) after a previous clean-up or pre-concentration step. Recoveries were in the ranges 93.2-102.6% and 91.3-102.9% for the commercial formulations and water samples, respectively.     

QTAIM charge-charge flux-dipole flux interpretation of electronegativity and potential models of the fluorochloromethane mean dipole moment derivatives

Infrared fundamental vibrational intensities and quantum theory atoms in molecules (QTAIM) charge-charge flux-dipole flux (CCFDF) contributions to the polar tensors of the fluorochloromethanes have been calculated at the QCISD/cc-pVTZ level. A root-mean-square error of 20.0 km mol(-1) has been found compared to an experimental error estimate of 14.4 and 21.1 km mol(-1) for MP2/6-311++G(3d,3p) results. The errors in the QCISD polar tensor elements and mean dipole moment derivatives are 0.059 e when compared with the experimental values. Both theoretical levels provide results showing that the dynamical charge and dipole fluxes provide significant contributions to the mean dipole moment derivatives and tend to be of opposite signs canceling one another. Although the experimental mean dipole moment derivative values suggest that all the fluorochloromethane molecules have electronic structures consistent with a simple electronegativity model with transferable atomic charges for their terminal atoms, the QTAIM/CCFDF models confirm this only for the fluoromethanes. Whereas the fluorine atom does not suffer a saturation effect in its capacity to drain electronic charge from carbon atoms that are attached to other fluorine and chlorine atoms, the zero flux electronic charge of the chlorine atom depends on the number and kind of the other substituent atoms. Both the QTAIM carbon charges (r = 0.990) and mean dipole moment derivatives (r = 0.996) are found to obey Siegbahn's potential model for carbon 1s electron ionization energies at the QCISD/cc-pVTZ level. The latter is a consequence of the carbon mean derivatives obeying the electronegativity model and not necessarily to their similarities with atomic charges. Atomic dipole contributions to the neighboring atom electrostatic potentials of the fluorochloromethanes are found to be of comparable size to the atomic charge contributions and increase the accuracy of Siegbahn's model for the QTAIM charge model results. Substitution effects of the hydrogen, fluorine, and chlorine atoms on the charge and dipole flux QTAIM contributions are found to be additive for the mean dipole derivatives of the fluorochloromethanes.