Non-metal-Metal transition in a non-crystalline carbon

We report a non-metal-metal transition found in a family of amorphous carbons. This transition is examined at the light of preliminary results on electrical conductivity, magnetoresistance and Hall effect. Data obtained on the thermal variation of the electrical conductivity are analysed in terms of the present trends of the theory.     

Relationships between Hg(II)-S bond distance and Hg(II) coordination in thiolates

Extended X-ray absorption fine structure (EXAFS) spectroscopy is a sensitive structural probe of the coordination environments of Hg(II) with thiol (sulfhydryl) groups, and is equally applicable to solid and aqueous organic or inorganic matter. Information on the number and geometric arrangement of S ligands can be derived from metal-ligand distances because the distances vary with Hg stereochemistry and can be accurately measured by the EXAFS technique. To improve the reliability of determining coordination structures of Hg with thiol groups, correlations among Hg-S bond distance, Hg coordination, and S-Hg-S angle in homoleptic Hg(II)-thiolates were calculated from analysis of the structures of the 162 Hg(SR)n motifs (n = 2, 3, 4) contained in the Cambridge Structural Database v. 5.28. Graphical correlations of bond distance with coordination number and with bond angle show distinct ranges of values characteristic of specific structural configurations.     

The mechanism of photo- and thermooxidation of poly(3-hexylthiophene) (P3HT) reconsidered

Poly(3-hexylthiophene) (P3HT) has been the focus of great interest as it is widely used in organic solar cells. However, P3HT has relatively poor photochemical and thermal stability under ambient atmosphere, which leads to a reduced lifetime of the solar cells. It was therefore necessary to study the photo- and thermooxidation of P3HT. Thin P3HT films were exposed to UV-visible light irradiation and thermal ageing, both in the presence of air. Changes in the infrared spectra of the aged samples were recorded, and the oxidation products were identified. A degradation mechanism that accounted for the modifications in the infrared spectra was then developed. This mechanism confirmed that singlet oxygen plays no decisive role, as previously reported. Oxidation was shown to involve the radical oxidation of the n-hexyl side-chains and the subsequent degradation of the thiophene rings. The breaking of the macromolecular backbone resulted in a loss of π-conjugation, provoking the bleaching of the sample.     

Determination of Hydrogen–Water Relative Permeability and Capillary Pressure in Sandstone: Application to Underground Hydrogen Injection in Sedimentary Formations

This paper presents fundamental analysis and micromechanical understanding of dense slurry behavior during settling in narrow smooth and rough slots. Particularly, this study seeks to contribute toward better understanding of dynamics of particle–particle and particle–wall interactions in viscous fluids using simple experiments. The findings of this study are applicable in a wide variety of problems, for example sediment transport, flow and transport of slurry in pipes, and industrial applications. However, the results interpretation focuses on better understanding of proppant flow and transport in narrow fractures. A sequence of experiments image frames captured by video camera is analyzed with particle image velocimetry (GeoPIV). The measurements include vertical velocities and displacement vectors of singular and agglomerated particles and larger area of formed slurry. Results present novel insights into the formation and effects of agglomerates on general slurry settling, and are supplemented with a comparison with previously published theoretical and empirical relationships. This work also emphasizes a role of particle–particle interactions in promoting agglomeration in viscous fluid. Particularly, a thin layer of viscous fluid between approaching particles dissipates particle kinetic energy due to lubrication effect. Lubrication effect is more pronounced when particles are constrained between two narrow walls and interact frequently with each other. Fluid tends to flow around agglomerated particles, and agglomerates remain stable for prolonged time periods gravitationally moving downward. The relative amount and size of agglomerated affects general settling of the slurry. It was found that fluid viscosity due to lubrication effect promotes agglomeration, and therefore, the overall slurry settling relatively increases at higher fluid viscosities. The results of the presented work have impact on various industrial and engineering processes, such as proppant flow and transport in hydraulic fractures, sand production in oil reservoirs, piping failure of dams and scour of foundation bridges.     

Involvement of Singlet Oxygen in the Solid‐State Photochemistry of P3HT

We studied the role that singlet oxygen plays in the solid‐state photochemistry of poly(3‐hexylthiophene) (P3HT). The photosensitized formation of singlet oxygen by solid‐state P3HT and its subsequent reactivity on the polymer were investigated. Using a fluorescent probe, it was found that singlet oxygen (¹O₂) could be produced by irradiation of P3HT by photosensitization, with no oxidation of the polymer. In addition, ¹O₂ was directly formed on P3HT via a chemical reaction, again with no oxidation of the polymer. These results give strong evidence that ¹O₂ is not the principal photo‐oxidative degradation intermediate of P3HT, which conflicts with previous reports.