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Environmental conditions can alter olfactory scent and chemical communication among biological species. In particular, odorant molecules interact with aerosols. Thermodynamics variables governing the adsorption from air to water surface of bombykol, the most studied pheromone, and of three derivative molecules, bombykal, bombykoic acid, and bombykyle acetate, are computed by steered and un-biased molecular dynamics in order to compare the role of their polar head group on adsorption on aqueous aerosols. When adsorbed, the molecule center of mass stands at about 1.2 Å from the interface and oscillates on the same length scale, trapped in an energy well. Gibbs energy of adsorption and desorption time of bombykol are found to be 9.2 kBT and 59 µs, respectively. The following ordering between the molecules is observed, reading from the more to the least adsorbed: bombykoic acid > bombykol > bombykoic acetate > bombykal. It originates from a complex interplay of entropy and enthalpy. The entropy and enthalpy of adsorption are discussed in the light of structural arrangement, H-bonding, and hydrophilic tail positioning of the molecules at the interface. Our results show that, when dispersed in the air, pheromones adsorb on aqueous aerosols. However, the individual residence time is quite short on pure water surfaces. Aerosols can, therefore, only have a decisive influence on chemical communication through collective effects or through their chemical composition that is generally more complex than that of a pure water surface. [ABSTRACT FROM AUTHOR]

In this article Part II, we consider the application of ienaic modeling for solvent extraction of rare earths in the case of the mixed DMDOHEMA/HDEHP extractant system. The system exhibits a synergistic extraction effect depending on the acid concentration and the extractant mole fraction, as demonstrated in the experimental article Part I. In this work, we directly compare experimental findings with theoretical predictions of the droplet model. The model considers the effective free energy of transfer as a combination of competing molecular forces, but contrary to previous micelle models that focus only on the dominant stoichiometry, it allows calculations of free energies of every possible spherical aggregate. The resulting image of the extraction process is that different behaviors can be obtained depending on the acidity and mole fraction of extractants, which are associated with different aggregation regimes in a complex free energy landscape of the system. Nevertheless, self-assembly is tuned by the extraction of all solutes, and not only the target metal cations. [ABSTRACT FROM AUTHOR]

Efficient formulations used in hydrometallurgy are often based on synergistic action of two oil-soluble extractants at an optimized mole fraction. In this series of two papers, we describe the N,N'-dimethyl-N,N'-dioctylhexylethoxymalonamide (DMDOHEMA)/di(2-ethylexyl) phosphoric acid (HDEHP) system, and how expression of the synergistic effect varies with acidity, using the three common representations: distribution ratios, yields, and free energies of transfer. The experimental results are detailed in this first part (Part I) with the so-called supramolecular approach, which considers the reverse micelle-like aggregates formed by the lipophilic extractant molecules. It shows that no specific aggregation state is observed at the maximum of synergism and antagonism. Besides, the critical aggregation concentration that characterizes the micellization free energy appears to follow some synergistic trends but cannot explain how acid tunes synergism to antagonism of this mixed system. Based on these results, Part II proposes a theoretical model based on the ienaic approach to interpret acid effect on synergism and antagonism. [ABSTRACT FROM AUTHOR]

Wood cell walls when contacted with humid atmosphere or an aqueous solution containing electrolytes or polymers undergo the phenomenon of swelling. In this work, experimental data were produced to quantify the effects of the adsorption water and solutes, which were introduced in the material by equilibration with a solution used as osmotic reservoir. For this reason, different environmental setups have been developed, allowing the control of temperature, water chemical potential, and ionic strength during the sorption process. The aim of this paper is to describe three experimental setups, focused on different levels: at the nanometric scale, small-angle scattering at controlled humidity; at the mesoscopic scale, environmental scanning electron microscopy; and at the macroscopic scale, tensile stage involving immersion of samples in solutions. Applicability and efficiency of the three setups are described. Moreover, it was shown how the combination of the results obtained via the three methodologies can be compared to expectations from a general Equation of State (EOS approach), where wood swelling with water and salt solutions is presented as the dependence of the distance between adjacent cellulose fibrils on the osmotic pressure. The total pressure calculated takes into account chemical, colloidal and mechanical terms in the force balance of the wood cell wall. [ABSTRACT FROM AUTHOR]

The corrosion process induced by evaporation of sessile droplets from aqueous sodium chloride solutions on planar iron surfaces was quantitatively investigated. The spatial distribution of the salt inside the evaporating sessile droplet, which is influenced by the initial salt concentration in the droplet bulk, is correlated to the localization of the anodic and cathodic reactions at the electrolyte-metal interface over the footprint droplet area. At low salt concentration, the inverse of the classical well-accepted Evans model is observed due to the hydrodynamic flows linked to evaporation: the anode area is established near the three-phase contact line region. Increasing salt concentration leads to a more uniform pitted sessile droplet: we observed locally anodic and cathodic areas over the droplet surface at the metal-electrolyte interface, where local variations in chloride concentrations occur. In addition, the presence of corrosion products and some pits demonstrate that pitting corrosion takes place if the salt concentration reaches a threshold value, experimentally determined by an optical set-up. [ABSTRACT FROM AUTHOR]

We study the addition of electrolytes to surfactant-free microemulsions in the domain where polydisperse pre-Ouzo aggregates are present. As in previous studies, the microemulsion is the ternary system water/ethanol/1-octanol, where ethanol acts as co-solvent. Addition of electrolytes modifies the static X-ray and neutron scattering, and dynamic light scattering patterns, as well as the position of the miscibility gap, where spontaneous emulsification occurs upon dilution with water. All observations can be rationalized considering that electrolytes are either “salting out” the ethanol, which is the main component of the interface stabilizing the aggregates, or producing charge separation via the antagonistic ion effect discovered by Onuki et al. Amphiphilic electrolytes, such as sodium dodecylsulfate or sodium dietheylhexylphosphate, induce a gradual transition towards monodisperse ionic micelles with their characteristic broad scattering “peak”. In these micelles the ethanol plays then the role of a cosurfactant. Dynamic light scattering can only be understood by combination of fluctuations of aggregate concentration due to the vicinity of a critical point and in-out fluctuations of ethanol. [ABSTRACT FROM AUTHOR]

The molecular organization of N,N'-dimethyl-N,N'-dioctylhexylethoxymalonamide (DMDOHEMA), the current reference extractant for the DIAMEX (DIAMide EXtraction) process, is correlated with its water extraction properties from neutral media. The aggregation of DMDOHEMA in n-heptane was investigated by vapor pressure osmometry (VPO) and the aggregate speciation characterized by combined small-angle neutron and X-ray scattering (SANS and SAXS, respectively). Two approaches were taken to model the aggregation of the diamide and the water extraction as a function of the diamide concentration by taking into account a single aggregation equilibrium with an average aggregation number N equal to 4.28 ± 0.05; and a competition between two types of aggregates in the organic phase, namely, aggregates of the reverse micelle type with 4 diamides per aggregate, and an oligomeric structure composed of about 10 diamide molecules which appears at high extractant concentration (>1 mol/L). In both cases, the supramolecular speciation representing the monomers/aggregates distribution was determined, and for each supramolecular organization, a solubilization parameter was calculated using the Sergievskii-Dannus relationship. Thus, the correlation between the two types of micellization of the diamide and the extraction of water into the organic phase was demonstrated. The larger aggregates can extract about five times more water than monomers. [ABSTRACT FROM AUTHOR]

Design features of a proposed high-resolution, high-speed powder diffractometer for operation at a synchrotron source are described. A key feature of the design is the use of imaging plates to record art almost complete range of data including both the high-angle and the small-angle scattering regime. The x-ray optics involve the use of a condensing-collimating channel-cut monochromator (CCCC) to achieve narrow parallel beams with cross sections of the order of 50 μm in the plane of diffraction, so that geometrical aberrations are very low and the beam cross section is well matched to the spatial resolution of the imaging plate detector. Angular resolution in 2θ of the diffractometer is easily variable, and designed to range from 0.01° upwards. Optional translation of the detector perpendicular to the incident-beam direction makes it possible to obtain time-resolved data. Applications of the instrument include high-resolution powder data collection for Rietveld analysis, studies of dynamic phenomena such as chemical reactions and phase transformations, particle-size determination, texture analysis, residual-stress measurements, single-crystal studies of the truncation-rod effect and surface scattering, microdiffraction, combined high-angle and small-angle scattering measurements, and studies of multilayer structures. As an illustration of the sort of results attainable with the proposed system, we present an oscillation photograph of the crystal-truncation rod effect for a Si wafer which was recorded at a synchrotron source using an imaging plate as the detector. [ABSTRACT FROM AUTHOR]

We extend a previous small-angle neutron scattering study of sodium octanoate (NaC) micelles to the ternary system sodium octanoate/pentanol/water. The use of contrast variation through selective deuteration of individual components together with explicit computation of interference effects, permits us to deduce the location of pentanol (COH) in the micelles. Our main conclusion is that, although the micelles grow as (COH) is solubilised, there is no concomitant variation in the NaC aggregation number. At low alcohol concentrations, the COH is located near the NaC polar heads, while at higher concentration the -OH groups are distributed throughout the micellar core. [ABSTRACT FROM AUTHOR]

We use the water corner of the model ternary system water/DDAB (a cationic double tailed surfactant)/LS (an uncharged single chain glycolipid) to investigate maximum swelling of a charged lamellar phase. The phase diagram is determined by visual observation and small angle neutron scattering. Upon the addition of the glycolipid in this mixed lamellar structure, a decrease of the maximum swelling is observed. A transition from vesicles to micelles is also evidenced in the dilute coexisting phase. By calculating explicitly the osmotic pressure in the micellar phase and in the lamellar phase through the Poisson-Boltzmann equation, we demonstrate that equilibrium of the osmotic pressure in the two phases and depletion of the lamellar phase by the micellar phase explain quantitatively the decrease of maximum swelling observed when the LS to DDAB ratio increases. [ABSTRACT FROM AUTHOR]