Motion of foam films in diverging-converging channels

Existing theories of the motion of foam films in capillaries often assimilate the pressure drop over the foam films to the static capillary pressure obtained from the Young-Laplace equation. Hence, they ignore the contribution of dynamic effects associated with the rapid stretching and contraction of the foam films to the overall viscous dissipation. This paper reports an investigation of the motion of foam films in axisymmetric diverging-converging channels, taking into account surface viscosity and elasticity. First, a phenomenological theory for the motion of the foam films is developed using simple physical arguments. We show that the displacement of the film obeys a nonlinear second-order differential equation, which can be solved numerically for the (dimensionless) distance from the inlet and the pressure drop as a function of time. Experiments with foam film motion, conducted using glass diverging-converging channels (minimum radius = 3.00 +/- 0,01 mm, maximum diameter = 7,98 +/- 0,01 mm) and nitrogen foam stabilized with sodium dodecyl sulfate (SDS) in brine, are discussed. For a single film motion in the diverging channel, we find that (a) the static pressure drop is a concave-upward function of distance and decreases from 1.0 to about 0.3, whereas (b) the dynamic pressure drop is concave downward and increases from 1 to a maximum of 1.3 and then decreases to 0.7. In the converging channel both the static and dynamic pressure drops are concave-downward functions, but the dynamic pressure drop values are always higher than the static ones. For two films the motions were found to be rather sensitive to the initial arrangement in the channel. The experiments are found to be in excellent agreement with the theoretical predictions. These observations imply that the large flow resistance obtained during foam flow in granular porous media, where converging-diverging channels are abundant, is largely due to the surface elasticity and viscosity of the films.     

Synthesis of a model system for the preparation of phloroglucinol containing natural products

A model system for the synthesis of phloroglucinol containing natural products was synthesized. Key steps include a manganic acetate-mediated cyclization and the facile conversion of an alkene into a β-bromoenone.     

Synthesis of aromatic polythioamide-oxothioxoquinazolines from bis(1,3,4-thiadiazoline-5-thione) and aromatic bis-o-amino esters

Aromatic polythioamide-oxothioxoquinazolines were synthesized by the polycondensation of 2,2′-(m-phenylene)bis-1,3,4-thiadiazoline-5-thione with aromatic bis-o-amino esters. The polymerizations were carried out at 160°C in acidic media such as m-cresol, sulfolane, and polyphosphoric acid to produce polymers with reduced viscosities up to 0.5 dL/g. These polymers were soluble in polar aprotic solvents like N-methyl-2-pyrrolidone and some acidic media including m-cresol. The polythioamide-oxothioxoquinazolines showed relatively good thermal stability with 10% weight loss at 344–394°C in air.     

Theoretical study on the structure and property relationship of the cationic conjugated polyelectrolytes

A theoretical study using density functional theory was performed to understand the structure/property relationship of the cationic conjugated polyelectrolytes, poly[9,9-bis-(6′-N,N,N-trimethylammonium) hexyl] fluorene-alt-4,7-(2,1,3-benzothiadiazole)] (PFBT-X, where X = Br). The torsion angle between the fluorene and benzothiadiazole units in the PFBT monomer was found to substantially affect the structural and electronic properties of the cationic PFBT monomer. The changes of geometrical parameter, HOMO and LUMO energy levels, and band gap, as well as the absorption maximum are discussed in terms of the torsion in the PFBT monomer structure. For comparison, its neutral analogue, the monomer of poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT) was also studied. The length of conjugation backbone was also examined.     

Chemistry of constrained dioxocyclam ligands with Co(III): unusual examples of C-H and C-N bond cleavage

The reactions between H(2)dc3 and Co(acac)(3) have been studied in the presence and absence of base. In the presence of base, a complex with an intramolecular Co-C bond, Co(dc3-C-(8))(H(2)O), 1, is formed, presumably through heterolytic C-H bond activation. An X-ray crystallographic study demonstrates the presence of a Co-C bond and shows that the diazacyclooctane (daco) subunit adopts the chair-boat conformation with respect to the metal. The cobalt-carbon bond induces strain in the macrocycle as demonstrated by bond angles significantly deviating from tetrahedral. The (13)C NMR resonance of the carbon atom bound to cobalt (-10.5 ppm) suggests significant ionic character in the cobalt-carbon bond. However, we were unable to cleave this bond in the presence of strong acid. In the absence of base, the reaction of Co(acac)(3) with H(2)dc3 resulted in C-N cleavage of the ligand and the formation of a complex of dioxocyclam, Co(dc)(acac), 2. This complex has subsequently been prepared in high yield by the reaction of Co(acac)(3) with dioxocyclam. An X-ray crystallographic study demonstrates that dioxocyclam adopts the heretofore unreported cis configuration, having folded along a N-Co-N axis that is perpendicular to the Co-acac plane.     

Chemical activation of carbon nanofibers and nanotubes

Method of thermodynamic simulation was used to calculate the equilibrium parameters of reactions of graphite with anhydrous LiOH, NaOH, and KOH and with the alkalis in the presence of water vapor. The change in the specific surface area and mass loss were used to analyze the interaction of carbon nanofibers and multilayer carbon nanotubes produced by catalytic pyrolysis of CH₄ with the alkalis.     

Domino "[3+3]-cyclization-homo-Michael" reactions of 1,3-bissilyl enol ethers with 1,1-diacylcyclopropanes

The Lewis acid mediated domino "[3+3]-cyclization-homo-Michael" reaction of 1,3-bissilyl enol ethers with 1,1-diacylcyclopropanes allows an efficient one-pot synthesis of functionalized salicylates containing a halogenated side chain. A great variety of substitution patterns could be realized by variation of the starting materials and of the Lewis acid. The mechanism of the domino process was studied.     

Impact of reaction products on the Grignard reaction with silanes and ketones

Grignard reactions with alkoxysilanes or carbonyl compounds produce alkoxymagnesium halides as by-products. Kinetic measurements for reactions of silanes and of a ketone were performed with Grignard reagents, enriched in alkoxymagnesium halides and taken in a great excess.The alkoxide-type reaction products complex tightly with Grignard reagents and enhance in this way their nucleophilicity, thus accelerating the reaction. However, alkoxides branched at α-C atom exert an unfavorable steric hindrance to reaction resulting in a decrease in the reaction rate.     

Synthesis of model long-chain ω-alkenyltrichlorosilanes and triethoxysilanes for the formation of self-assembled monolayers

The synthesis of model long-chain hydrocarbons (C₁₃ and C₁₉) carrying a vinyl group and a trichloro- or a triethoxysilyl group at each end is reported. These compounds are suitable for linkage to a hydroxylated silicon surface and at the other end with vinyl group for further functionalization and multilayer formation.     

Reactive dications: the superacid-catalyzed reactions of alkynes bearing adjacent N-heterocycles or amine groups

A variety of aminoalkynes and related heterocycles are reacted in the Bronsted superacid CF(3)SO(3)H (triflic acid), and products are obtained in generally good yields (69-99%) from Friedel-Crafts-type reactions. The reactions are consistent with the formation of novel dicationic intermediates having a vinyl cationic site and an adjacent protonated N-heterocycle or ammonium cation.