Rheological behavior of water-in-oil emulsions stabilized by hydrophobic bentonite particles

A study of the rheological behavior of water-in-oil emulsions stabilized by hydrophobic bentonite particles is described. Concentrated emulsions were prepared and diluted at constant particle concentration to investigate the effect of drop volume fraction on the viscosity and viscoelastic response of the emulsions. The influence of the structure of the hydrophobic clay particles in the oil has also been studied by using oils in which the clay swells to very different extents. Emulsions prepared from isopropyl myristate, in which the particles do not swell, are increasingly flocculated as the drop volume fraction increases and the viscosity of the emulsions increases accordingly. The concentrated emulsions are viscoelastic and the elastic storage and viscous loss moduli also increase with increasing drop volume fraction. Emulsions prepared from toluene, in which the clay particles swell to form tactoids, are highly structured due to the formation of an integrated network of clay tactoids and drops, and the moduli of the emulsions are significantly larger than those of the emulsions prepared from isopropyl myristate.     

Detailed analysis of modifications in lignin after treatment with cultures screened for lignin depolymerizing agents

Termites, beetles, and other arthropods can digest living and decaying wood plus other lignocellulosic plant litter. Microbial sources like other wood-eating insect guts and wastewater treatment sludge were screened for lignin depolymerization. Near infrared spectroscopy and atomic force microscopy (AFM) along with high-performance liquid chromatography (HPLC), were used to track changes in functional groups, size, shape, and molecular weight of lignin molecules during incubations. Odontotaenius disjunctus (Betsy beetle) guts dissected whole or separately as midgut, foregut, and hindgut, consumed corn stover but did not show lignin depolymerization. The sludge-treated lignin did show some reduction in molecular weight on the HPLC, particle size (350–650 nm initially to 135–220 nm by day 30) and particles per field on AFM. pH and the presence of nutrients had a substantial effect on the extent of depolymerization. Cultures in lignin and nutrients showed higher growth than cultures with lignin only. Colony characteristics within the beetle gut and the sludge were also evaluated.     

Synthesis, characterization and DFT studies of the cobalt(III) complex of a tetrapodal pentadentate N4S donor ligand

The synthesis of the pentadentate ligand 2,6-bis(3,3-dimethyl-2,4-dioxocyclohexanyl)-4-thiaheptane (N4Samp) is described. The synthetic pathway involves the coupling of two 1,3-(dimethylenedioxy)-2-methyl-2-(methylene-p-toluenesulfonyl)propane moieties with sodium sulfide and subsequent synthetic elaboration to prepare the final N4S donor system. The cobalt(III) complex [Co(N4Samp)Cl]2+ has been prepared and subsequently crystallized as the tetrachlorozincate salt. The X-ray structure analysis confirms the pentadentate nature of the ligand and shows the thioether donor occupying one apex with four equivalent amine donors effectively occupying the equatorial plane of the molecule. The sixth coordination site is occupied by a chloro ligand. The electronic absorption and 13C NMR spectra have been studied. DFT calculations have been employed to explore structural and mechanistic comparisons between [Co(N4Samp)Cl]2+ and an analogous pentaaamine complex.     

Coordination of pertechnetate [TcO4]- to actinides

The ability of [TcO(4)](-) to coordinate directly to tetra- and hexa-valent actinides in the presence of organic P[double bond, length as m-dash]O ligands is confirmed in the crystallographically characterised complexes [UO(2)(TcO(4))(2)(Ph(3)PO)(3)] and [Th(TcO(4))(4)((n)Bu(3)PO)(4)].     

High order finite volume approximations of differential operators on nonuniform grids

When computing numerical solutions to partial differential equations, difference operators that mimic the crucial properties of the differential operators are usually more accurate than those that do not. Properties such as symmetry, conservation, stability, and the duality relationships and identities between the gradient, curl, and divergence operators are all important. Using the finite volume method, we have derived local, accurate, reliable and efficient difference methods t divergence, gradient, and curl operators are defined using a discrete versions of the divergence theorem and Stokes' theorem. These methods are especially powerful on coarse nonuniform grids and in calculations where the mesh moves to track interfaces or shocks. Numerical examples comparing local second and fourth-order finite volume approximations to conservation laws on very rough grids are used to demonstrate the advantages of the higher order methods.     

A simple amine protection strategy for olefin metathesis reactions

Acyclic diamines are valuable feedstocks for polyamide synthesis. Ruthenium-alkylidene catalysed cross metathesis of amino alkenes is problematic and acyl derivatisation can result in less efficient syntheses, poor catalyst turnover and isomerisation. Temporary amine masking via stable and soluble ammonium salts delivers cyclic and acyclic aminoalkenes in high yield and purity.     

Investigations of rotamers in diaxial Sn(IV)porphyrin phenolates—towards a molecular timepiece

An approach to the formation of molecular timepieces is outlined based on differentiating between rotamers in diaxial Sn(IV) porphyrin phenolates. Two models are explored in detail. The first explores how the rates of rotation of the diaxial ligands is discriminated based on steric hindrance of the two porphyrin macrocycle faces at low temperature. The second model explores a ‘stopwatch’ function based on the ligation of Ag(I) ions to a 5,15-dipyridylporphyrinato tin(IV) complex bearing 3-hydroxypyridine ligands. The complexation inhibits rotation of the axial ligand, a result, which can be reversed by precipitation of Ag(I) using tetraethylammonium bromide. X-ray crystallography has also been used to characterize two Ag(I) 5,15-dipyridylporphyrinato tin(IV)complexes. The two isoforms differ in their supramolecular organization. One structure is formed through a cofacial stack linking each porphyrin by Ag(I) coordination. The other displays a sheet-like coordination polymer structure.     

Construction of multiporphyrin arrays via selective cross-metathesis

Selective cross-metathesis of type I and type II meso-functionalized porphyrin olefins afforded alkenyl-coupled dimeric and trimeric porphyrin systems in good yield with excellent E/Z selectivity. The synthetic utility of the method is demonstrated through the preparation of mixed metalated (M = 2H, Zn) porphyrin dimer and trimer. [reaction: see text]     

Small solid particles and liquid lenses at fluid/fluid interfaces

The behaviour of small solid particles and liquid droplets at fluid interfaces is of wide interest, in part because of the roles they play in the stability of foams and emulsions. Here we focus on solid particles at liquid interfaces, both singly and in highly structured monolayers. We briefly mention small oil lenses on water in connection with the determination of line tension, τ. Particles are surface-active in the sense that they often adhere quite strongly to liquid surfaces, although of course they are not usually amphiphilic. The three-phase contact line around a particle at an interface is associated with an excess free energy resulting in a tendency of the line to contract (positive τ, which is a 1D analogue of surface tension) or to expand (negative τ). Positive line tension acts so as to push the contact angle of a particle with the fluid interface further away from 90°, i.e. to force the particle towards the more “wetting” of the two bulk phases. It also leads to activation barriers to entry and departure of particles from an interface. The behaviour of particle monolayers at octane/water interfaces is also discussed . It is found that, for monodisperse spherical polystyrene particles containing ionisable sulphate groups at the surface, highly ordered monolayers are formed. This appears to result from very long range electrostatic repulsion mediated through the oil phase. Surface pressure–surface area isotherms are discussed for particle monolayers and it is shown, using light microscopy, that at monolayer “collapse” particles are not expelled from the monolayers but rather the monolayer folds, remaining intact. This has an important bearing on methods, involving the use of the Langmuir trough, for the experimental determination of contact angles and line tensions in particulate systems. Received: 18 July 1999/Accepted: 30 August 1999     

A characteristic-Galerkin approximation to a system of shallow water equations

Summary. Characteristic methods are known to handle advective flow better than traditional Galerkin methods and allow large time steps to be taken when compared to standard time-stepping methods. In this paper, we investigate a characteristic-Galerkin approximation to the 2-dimensional system of shallow water equations. We derive bounds for elevation and velocity, showing these to be optimal for velocity in . Received October 15, 1998 / Revised version received March 13, 1999 / Published online April 20, 2000