Structure and stability of silica particle monolayers at horizontal and vertical octane-water interfaces

Monolayers of silica particles at horizontal and vertical octane-water interfaces have been studied by microscopy. It is found that their structure and stability depend strongly on the particle hydrophobicity. Very hydrophobic silica particles, with a contact angle of 152 degrees measured through the water, give well-ordered monolayers at interparticle distances larger than 5 particle diameters which are stable toward aggregation and sedimentation. In contrast, monolayers of less-hydrophobic particles are disordered and unstable. Two-dimensional particle sedimentation has been observed in the case of vertical monolayers. The results have been analyzed with a simple two-particle model considering the sedimentation equilibrium as a balance between the long-range electrostatic repulsion through the oil, the gravity force, and the capillary attraction due to deformation of the fluid interface around particles. The value of the charge density at the particle-octane interface, 14.1 muC/m(2), found for the most hydrophobic particles is reasonable. It drastically decreases for particles with lower hydrophobicity, which is consistent with the order-disorder transition in monolayer structure reported by us before. The pair interactions between particles at a horizontal octane-water interface have been analyzed including the capillary attraction due to undulated three-phase contact line caused by nonuniform wetting (the contact angle hysteresis). The results are in agreement with the great stability of very hydrophobic silica particle monolayers detected experimentally, even at low pH at the point of zero charge of the particle-water interface, and with the aggregated structure of hydrophilic particle monolayers.     

Novel film-calliper method of measuring the contact angle of colloidal particles at liquid interfaces

A simple and reliable film-calliper method of measuring the particle contact angle at the water-air (oil) interface in real time has been developed. Its applicability to submicrometer and micrometer latex and silica particles is demonstrated.     

In situ spectroscopy and spectroelectrochemistry of uranium in high-temperature alkali chloride molten salts

Soluble uranium chloride species, in the oxidation states of III+, IV+, V+, and VI+, have been chemically generated in high-temperature alkali chloride melts. These reactions were monitored by in situ electronic absorption spectroscopy. In situ X-ray absorption spectroscopy of uranium(VI) in a molten LiCl-KCl eutectic was used to determine the immediate coordination environment about the uranium. The dominant species in the melt was [UO 2Cl 4] (2-). Further analysis of the extended X-ray absorption fine structure data and Raman spectroscopy of the melts quenched back to room temperature indicated the possibility of ordering beyond the first coordination sphere of [UO 2Cl 4] (2-). The electrolytic generation of uranium(III) in a molten LiCl-KCl eutectic was also investigated. Anodic dissolution of uranium metal was found to be more efficient at producing uranium(III) in high-temperature melts than the cathodic reduction of uranium(IV). These high-temperature electrolytic processes were studied by in situ electronic absorption spectroelectrochemistry, and we have also developed in situ X-ray absorption spectroelectrochemistry techniques to probe both the uranium oxidation state and the uranium coordination environment in these melts.     

Rapid determination of isocitrate dehydrogenase mutation status of human gliomas by extraction nanoelectrospray using a miniature mass spectrometer

Analytical and Bioanalytical Chemistry - Isocitrate dehydrogenase (IDH) I and II mutations in gliomas cause an abnormal accumulation of 2-hydroxyglutarate (2-HG) in these tumor cells. These...     

Particle film growth driven by foam bubble coalescence

Water films stabilised by hydrophobic particles are found to spread rapidly up the inner walls of a glass vessel containing water and hydrophobic particles when it is shaken; shaking produces unstable particle-stabilised foam bubbles whose coalescence with the air/water interface drives film growth up the inner walls of the container.     

The coordination of perrhenate and pertechnetate to thorium(IV) in the presence of phosphine oxide or phosphate ligands

A series of thorium(IV) perrhenato- and pertechnetato-complexes with P[double bond, length as m-dash]O donor ligands have been prepared and characterised both in the solid state and in solution. Isostructural complexes of general formula [Th(MO(4))(4)(L)(4)], where M = Re or Tc and L = triethylphosphate (TEP) (2 and 7), tri-iso-butylphosphate (TiBP) (3 and 8) and tri-n-butylphosphine oxide (TBPO) (4 and 9) have been prepared from the novel starting materials [Th(ReO(4))(4)] x 4H(2)O (1) and [Th(TcO(4))(4)] x 4H(2)O (6). The reaction of or with triphenylphosphine oxide (TPPO) in MeOH has also led to the synthesis of [Th(MO(4))(3)(TPPO)(3)(OCH(3))(HOCH(3))] (M = Re (5) or Tc (10)). While the structural characterisation of 4 and 9 has been previously described, we report for the first time the structural characterisation of 2 and 5, with a partial structural refinement of 3. Vibrational spectroscopic analysis confirms that the Tc complexes not characterised by single crystal X-ray diffraction are indeed isostructural with the perrhenate complexes with the same P[double bond, length as m-dash]O donor ligand. In all cases, monodentate coordination of the Group 7 tetraoxo anion is observed. (31)P NMR spectroscopy indicates that in all the phosphine oxide-based complexes there is one dominant solution species. For the phosphate based systems, the presence of pertechnetate appears to inhibit P[double bond, length as m-dash]O donor ligand complexation in solution, whereas a significant proportion of each phosphate remains coordinated to Th(IV) when perrhenate is present as the counter ligand. These results give some indication as to the mechanism of pertechnetate co-extraction with tetravalent cations in the presence of tri-n-butyl phosphate in the Plutonium and Uranium Recovery by Extraction (PUREX) process.     

Progress in charge transfer systems utilizing porphyrin donors and simple aromatic diimide acceptor units

An overview of the evolution of artificial photosynthetic charge transfer systems containing porphyrin donors and pyromellitic or naphthalene diimide acceptor units is presented. Progression in this area of research is highlighted by the complexity of the systems, the nature of the medium separating donor and acceptor as well as the progression in the lifetime of the charge-separated state upon photoexcitation. A number of supramolecular systems that utilize hydrogen bonding or axial ligation of zinc porphyrins as a means for spatial orientation are highlighted.     

A double-stage tube furnace—acid-trapping protocol for the pre-concentration of mercury from solid samples for isotopic analysis

High-precision mercury (Hg) stable isotopic analysis requires relatively large amounts of Hg (>10 ng). Consequently, the extraction of Hg from natural samples with low Hg concentrations (<1–20 ng/g) by wet chemistry is challenging. Combustion–trapping techniques have been shown to be an appropriate alternative [1]. Here, we detail a modified off-line Hg pre-concentration protocol that is based on combustion and trapping. Hg in solid samples is thermally reduced and volatilized in a pure O₂ stream using a temperature-programmed combustion furnace. A second furnace, kept at 1,000 °C, decomposes combustion products into H₂O, CO₂, SO₂, etc. The O₂ carrier gas, including combustion products and elemental Hg, is then purged into a 40 % (v/v) acid-trapping solution. The method was optimized by assessing the variations of Hg pre-concentration efficiency and Hg isotopic compositions as a function of acid ratio, gas flow rate, and temperature ramp rate for two certified reference materials of bituminous coals. Acid ratios of 2HNO₃/1HCl (v/v), 25 mL/min O₂ flow rate, and a dynamic temperature ramp rate (15 °C/min for 25–150 and 600–900 °C; 2.5 °C/min for 150–600 °C) were found to give optimal results. Hg step-release experiments indicated that significant Hg isotopic fractionation occurred during sample combustion. However, no systematic dependence of Hg isotopic compositions on Hg recovery (81–102 %) was observed. The tested 340 samples including coal, coal-associated rocks, fly ash, bottom ash, peat, and black shale sediments with Hg concentrations varying from <5 ng/g to 10 μg/g showed that most Hg recoveries were within the acceptable range of 80–120 %. This protocol has the advantages of a short sample processing time (～3.5 h) and limited transfer of residual sample matrix into the Hg trapping solution. This in turn limits matrix interferences on the Hg reduction efficiency of the cold vapor generator used for Hg isotopic analysis.     

MPSA effects on copper electrodeposition investigated by molecular dynamics simulations

In superconformal filling of copper-chip interconnects, organic additives are used to fill high-aspect-ratio trenches or vias from the bottom up. In this study we report on the development of intermolecular potentials and use molecular dynamics simulations to provide insight into the molecular function of an organic additive (3-mercaptopropanesulfonic acid or MPSA) important in superconformal electrodeposition. We also investigate how the presence of sodium chloride affects the surface adsorption and surface action of MPSA as well as the charge distribution in the system. We find that NaCl addition decreases the adsorption strength of MPSA at a simulated copper surface and attenuates the copper-ion association with MPSA. The model also was used to simulate induced-charge effects and adsorption on a nonplanar electrode surface.